Biol. Chem. 2015; 396(5): 483–494
Review
Karl-Josef Dietz* and Rüdiger Hell
Thiol switches in redox regulation of chloroplasts:
balancing redox state, metabolism and oxidative
stress
Abstract: In photosynthesizing chloroplasts, rapidly
changing energy input, intermediate generation of strong
reductants as well as oxidants and multiple participating physicochemical processes and pathways, call for
efficient regulation. Coupling redox information to protein function via thiol modifications offers a powerful
mechanism to activate, down-regulate and coordinate
interdependent processes. Efficient thiol switching of target proteins involves the thiol-disulfide redox regulatory
network, which is highly elaborated in chloroplasts. This
review addresses the features of this network. Its conditional function depends on specificity of reduction and
oxidation reactions and pathways, thiol redox buffering,
but also formation of heterogeneous milieus by microdomains, metabolite gradients and macromolecular assemblies. One major player is glutathione. Its synthesis and
function is under feedback redox control. The number
of thiol-controlled processes and involved thiol switched
proteins is steadily increasing, e.g., in tetrapyrrole biosynthesis, plastid transcription and plastid translation.
Thus chloroplasts utilize an intricate and versatile redox
regulatory network for intraorganellar and retrograde
communication.
Keywords: Arabidopsis thaliana; chloroplast; glutathione;
redox regulation; thiol switch.
DOI 10.1515/hsz-2014-0281
Received November 29, 2014; accepted March 2, 2015; previously
published online March 5, 2015
*Corresponding author: Karl-Josef Dietz, Biochemistry and
Physiology of Plants, Faculty of Biology, W5-134, Bielefeld
University, University Street 25, D-33501 Bielefeld, Germany,
e-mail: [email protected]
Rüdiger Hell: Centre for Organismal Studies, University of
Heidelberg, Im Neuenheimer Feld 360, D-69120 Heidelberg,
Germany
Introduction: the challenge –
regulation in photosynthesizing
chloroplasts
Photosynthesis consists of a complex series of redox reactions. The balance between light harvesting, physicochemical energy conversion and metabolic consumption
of chemical energy determines the redox state of participating reactions. Thus the redox milieu of chloroplasts
rapidly changes in dependence on the photosynthetic
state, which, in turn, depends on environmental conditions such as light intensity, temperature and CO2 availability. Thereby the redox milieu provides important
information on the metabolic state and thus the systems
performance of photosynthesis (Scheibe and Dietz, 2012).
Chloroplasts, unlike any other organelle, alter their
energization state and reduction potential in immediate
response to environmental cues on shortest time scales of
less than 1 s. Adjustment of photosynthesis to changing
photon flux densities serves as the best example because
light intensities drop or rise by shading in combination
with moving sun flecks or wind. Maximum photosynthetic CO2-fixation rates reach 400 μmol CO2/mg chlorophyll h corresponding to linear electron transport rates
from water to NADP+ of 12 mmol electron/ls or 6 mmol
NADPH/ls (calculated based on 40 μl chloroplast volume/
mg chlorophyll). Considering the total NADPH concentration of 50–100 μm, such rates correspond to 60- to 120fold turnover per second. Light intensities change within
seconds in the natural environment and instantaneously
in the ­laboratory or growth chamber. A small NADPH pool
with tremendous turnover represents a sensitive redox
hub in the chloroplast. But plants efficiently cope with
these rapid metabolic challenges. Obviously, they are able
to coordinate light harvesting and light-driven generation of reducing power with its consumption in metabolism under most conditions almost instantaneously
­(Puthiyaveetil et al., 2012; Shikanai, 2014).
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484 K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation
The redox milieu of the chloroplast
Excessively accumulating reducing power in the photosynthesizing chloroplast strongly affects redox homeostasis
and normal cell functions. Reactive oxygen species (ROS)
or other reactive intermediates are generated by transfer
of electrons to oxygen if the final electron acceptor NADP+
is unavailable. Thus over-reduction is linked to ROSmediated oxidative switching of redox sensors and redox
signaling, but may also cause oxidative damage. Nonaqueous chloroplasts isolated from Beta vulgaris or Spinacia oleracea leaves reflect the specific metabolic situation
of the chloroplasts in vivo and revealed that the NADPH/
(NADP+NADPH) ratio in chloroplasts increases from 0.22
to 0.32 in the dark to 0.33–0.52 after 15 s of illumination
with 700 μmol quanta m-2 s-1. Reaching a slightly higher
maximum after 30 s of illumination, the ratio returned to
the dark levels after about 3 min in the light (Heber and
Santarius, 1965). This rapid activation testifies the efficient
coordination of light and dark reactions of photosynthesis.
These data also imply that the system usually adjusts to a
rather oxidizing NADPH/NADP redox state.
Over-reduction of the photosynthetic electron transport chain (PET) describes a state of accumulated reduced
electron carriers with very negative redox potential. Several
non-invasive methods allow for determination of PET redox
and energization state, e.g., redox state of the primary
acceptor of photosystem II QA, reduction state of photosystem I, the electrochromic shift measured near 520 nm
and light scattering of leaves (Kobayashi et al., 1982; Takizawa et al., 2007). Such measurements with leaves in vivo
as well as with isolated chloroplasts and thylakoids show
a relationship between PET over-reduction and enhanced
production of reactive molecular species, namely singlet
oxygen, superoxide, hydrogen peroxide, lipid peroxides
and other reactive species. Such reactive species oxidize
macromolecules of the cell interfering with their normal
function. Such redox changes are used for tuning protein
activity and thus metabolic rates, in other cases these
changes trigger degradation of damaged macromolecules, or they initiate cell death program. M
­ onitoring and
controll­ing the redox state of the PET and the chloroplast
stroma is central to counteract over-­reduction and avoid
the development of threatening oxidative stress.
In technical devices that need accurate process regulation, monitoring mechanisms sense the state of important elements within the system. Deviations from norm
levels initiate feedback to adjust the desired condition. In
contrast to simple circuitries often utilized in technology
biological systems commonly use multiple control mechanisms. Regulation of photosynthesis employs multiple
inputs and tuning mechanisms. In fact the superior performance of sophisticated cross-talking control networks
is nowadays realized also in technology where board computers control the entire system.
The catchiest in vivo and thus ‘on line’-observation of
regulation involved in photosynthesis was reported and
studied in particular by Walker’s group (Sheffield, UK).
They explored oscillations in photosynthetic parameters that can be observed in many plant species under
conditions, such as low phosphate supply, low temperature, high CO2-concentrations, or re-illumination after
a short dark period. Photosynthetic gas exchange, chlorophyll fluorescence, but also biochemical parameters
start to oscillate with initially high amplitude and subsequent dampening to the new steady state (Figure 1).
Oscillations testify overshooting responses of regulation
(Walker, 1992). In fact Laisk proposed that understanding
Light
switch
1.6
5.9
ATP/ADP
0.5
0.17
NADPH/NADP+
CO2-fixation rate
PSI
oxidation
PSI reduction
PSI redox state
Fluorescence maximum
Chlorophyll fluorescence
Energization:
Maximum
535 nm (light scattering)
Minimum
Membrane potential
518 nm
1 min
0.001 ∆Abs
Figure 1: Oscillations in photosynthesis witness regulation and
limitations.
In the 1990s, considerable effort was directed towards dissecting
the mechanistic basis for photosynthetic oscillations commonly
seen upon introducing disturbances (Walker, 1992). The figure combines data from several studies (Sivak et al., 1985; Laisk et al., 1991;
Walker, 1992) and shows the delay between minima and maxima of
different physicochemical parameters, namely electrochromic shift
at 518 nm, light scattering (at 535 nm), PSI redox state, chlorophyll
fluorescence emission and CO2 fixation rate. The PSI signal started
from a high level, and oscillations were only visualized after amplification. For this reason the recording is shown in two amplifications,
which may explain the apparent lack of oscillations after switching
on the light. These data were obtained with spinach leaves exposed
to sudden reillumination. Also shown are the NADPH/NADP+
and ATP/ADP-ratios in the minimum and maximum (Laisk et al.,
1991). The metabolic data are from sunflower. See text for detailed
discussion.
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K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation 485
oscillations would be equivalent to understanding regulation of photosynthesis (Laisk et al., 1991; Walker, 1992).
Figure 1 shows that each measured parameter showed a
specific pattern of consecutive maxima and minima. Following a minimum in energization as indicated by light
scattering, there occurred a minimum in thylakoid membrane potential (electrochromic shift at 518 nm). This was
paralleled by increased reduction of photosystem I and
high fluorescence emission. With slight delay CO2 fixation
reached a minimum. Subsequently, all the changes were
mirrored in opposite direction, i.e., maximum in energization, maximum in membrane potential, minima in
PSI reduction and fluorescence followed by maximal CO2
fixation (Sivak et al., 1985; Walker, 1992). Determination of
NADPH and NADP+, as well as ATP and ADP (Laisk et al.,
1991) revealed the surprising fact that maximal CO2 fixation coincided with high ATP/ADP ratios but with minima
in NADPH/NADP+ (Figure 1). Maxima in NADPH/NADP+
were preceded by maximal reduction of PSI. Therefore,
Laisk et al. (1991) concluded that imbalanced supply of
reducing power in form of NADPH and phosphorylation
potential represent the cause for oscillations in photosynthesis. Apparently, redox processes, e.g., alterations
between high and low electron pressure (PSI, 518 nmshift, NADPH/NADP+) participate in this phenomenon.
Oscillations depend on delays in regulatory response
time. It is tempting to speculate that thiol-dependent activation of the Calvin cycle is crucially involved in triggering the oscillations, namely if high reduction state of PSI
diverts electrons into the thioredoxin system which in turn
‘over’-activates committed enzymes of photosynthetic
metabolism. ‘Over-activation’ may subsequently cause a
collapse in energization and inhibition of thiol-regulated
target proteins below the needed rates in balance with
light energy input. Thus in the next step energization will
increase and reach the next maximum.
Thiol regulation in chloroplasts
The thiol redox state constitutes one of the most important
process parameters in chloroplasts. Several redox players
serve as hubs in the redox network of the chloroplast and
thus act as information-rich agents in chloroplast signaling (Figure 2). (i) the plastoquinone (PQ) redox state
provides integrated information on light conversion into
excitation and activity of reaction centers of photosystem I
relative to photosystem II (Rochaix, 2013). (ii) C
­ hloroplast
ferredoxin (Fd) functions as distributor of electrons
between Fd-dependent NADP reductase, Fd-dependent
Thylakoid lumen
Stroma
PQ
STN7/8
Fd
NADPH
GSH
Trx
NTRC
Grx
Regulatory targets (enzymes, kinases, translation factors)
CO2
Metabolism
Translation
Gene
expression
Export for retrograde signaling
Figure 2: Redox regulatory hubs in context of photosynthetic
­electron transport chain.
Three major pathways feed information on redox state into the
redox regulatory network of the chloroplast, the intersystem
electron transport, the ferredoxin/thioredoxin (Fd/Trx) system,
the NADPH/NADPH thioredoxin reductase C (NTRC)-system, the
glutathione/glutaredoxin (GSH/Grx)-system. This information
is processed to control organellar transcription, translation and
metabolism or after exported to the cytosol to modulate extraplastidic processes by retrograde mechanisms.
thioredoxin reductase, nitrite reductase, sulfite reductase,
Fd-dependent glutamine-oxoglutarate amidotransferase
(Fd-GOGAT), cyclic electron transport and others (Blanco
et al., 2013). (iii) NADPH delivers reducing power to metabolic reactions. (iv) glutathione buffers thiol-disulfide
redox state and is present in millimolar concentrations.
Glutathione has additional functions as electron donor for
reduction of dehydroascorbate in the water/water cycle,
which detoxifies hydrogen peroxide (Miyake, 2010). Likewise Trx, glutathione/glutaredoxins and NADPH-dependent thioredoxin reductase C (NTRC) feed electrons into the
peroxiredoxin system for detoxifying hydrogen peroxide,
alkylhydroperoxides and peroxinitrite (Dietz, 2011).
Each of these redox hubs is linked to sensory systems.
Figure 2 schematically links PQ redox state to the protein
kinases STN7/8, which control the phosphorylation state
of photosynthetic proteins. Electron channeling from Fd
to multiple Trx isoforms controls specifically the redox
state of diverse dithiol-disulfide-target proteins. Targets
such as sedoheptulose-1,7-bisphosphatase (SBPase) and
fructose-1,6-bisphosphatase (FBPase) are classical thiol
switches in the chloroplast (Schürmann and Wolosiuk,
1978; Yoshida et al., 2014). NADPH feeds electrons into
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486 K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation
diverse metabolic reactions and also into the NTRC system,
which will be discussed below. Glutathione concentration
and redox state control S-glutathionylation of chloroplast
target proteins in tight interaction with chloroplast glutaredoxins (Zaffagnini et al., 2012). Applying this concept of
regulation to the example of photosynthetic oscillations
described above, one has to consider the relative concentrations of redox transmitters, in particular thioredoxins,
the concentration of target proteins and the kinetics of
activation in order to address the hypothesis that thiol
redox regulation might be involved as delay factor triggering phase separation of processes and thus oscillations:
Proteomics studies have revealed that thioredoxins are
low abundant proteins relative to their target proteins
(Peltier et al., 2006). Thus the concentrations of SBPase
and FBPase appear to exceed the concentration of thioredoxin f1 by a factor of more than 1000. This unfavorable
ratio contrasts the conditions of in vitro enzyme assays
where Trx f1 is typically added in excess and maximum
activation is only seen at high molar ratios of Trxf1/FBPase
(de Lamotte-Guery et al., 1991). Knowledge on reoxidation
of target enzymes is not available. Interestingly, SBPase
was among the targets easily oxidized in vivo upon methylviologen treatment (Muthuramalingam et al., 2013). This
result shows that oxidation occurs, but involved mechanisms such as oxidation by Trx-disulfide, direct oxidation
by H2O2, proximity based oxidation or other reactions still
need to be identified (König et al., 2012).
Modulation of the glutathione hub
in chloroplasts
Glutathione in plants is associated with many functions
in addition to ROS scavenging and redox regulation
(Noctor et al., 2012). Its role is therefore intertwined with
meta­bolism, in particular the assimilation of sulfate in
­chloroplasts. The relevant parameters for the redox potential of glutathione are its concentration and the GSH to
GSSG ratio according to the Nernst equation. Synthesis,
intracellular exchange and adjustment of reducing capacity of glutathione are decisive factors for understanding
modulation of downstream targets of photosynthesis and
stress acclimation (Ball et al., 2004; Meyer and Rausch,
2008). However, as glutathione appears to be present in
most compartments of plant cells, the analysis and interpretation of glutathione functions still suffer from technical limitations that enable analyses of whole organ
or tissue levels but impede differentiation between cell
types and subcellular compartments. This limitation can
currently only be overcome by non-aqueous fractionation and live cell imaging but most of the existing datasets
are predominately derived from whole-tissue analyses.
According to these reports, disturbances of redox homeostasis based on the total content of glutathione, of the
ratio of GSH to GSSG towards oxidation and increased
expression or enzyme activity of glutathione reductase
(GR) have frequently been reported in response to stress
factors, such as high light, osmotic factors and pathogen
infection, all causing enhanced formation of ROS [see
reviews by Klapheck et al. (1987); May et al. (1998); Tausz
et al. (2004); Rausch and Wachter (2005); Hell and Kruse
(2007); Noctor et al. (2011, 2012)].
An estimated one-third of total glutathione content of
leaves can be attributed to chloroplasts (Klapheck et al.,
1987) with estimations ranging from 1 to 4.5 mm in chloroplasts (Bergmann and Rennenberg, 1993; Noctor and Foyer,
1998). Arabidopsis leaves contain an averaged glutathione
pool of 0.7 mm. Non-aqueous fractionation revealed nearly
equal glutathione pools with 3–4 mm concentrations in
the cytosol and chloroplasts (Krüger et al., 2009). For comparison, the overall cysteine concentration was 17 μm but
only 9 μm of cysteine was determined in chloroplasts and
3 μm in the cytosol (Krüger et al., 2009). GSH/GSSG ratios
have not been determined by non-aqueous fractionation
nor potential changes in the distribution of glutathione
within cells in response to stress. However, with respect
to glutathione these results (Krüger et al., 2009) suggest
equilibrium between the pools in both compartments at
least under non-stressed conditions due to exchange processes as outlined below. Thus, significant changes of total
glutathione pools may similarly affect both compartments
and therefore also redox processes triggered by glutathione
in the chloroplasts. Whether this assumption also holds
for short-term disturbances of glutathione homeostasis is
unclear. In fact most reports focus on time points several
hours or even days after onset of stress. A time resolved
analysis in response to high light revealed an increase in
GSH levels after 30 min in normal light grown Arabidopsis
thaliana that was exposed to 10-fold light increase and 1
h, respectively, in shade-acclimated plants transferred to a
100-fold higher photon flux density (Alsharafa et al., 2014).
The promise of redox probes and
cell imaging in plants
The contribution of chloroplast glutathione pools to stress
defense and the cell-specificity of responses are difficult
to assess owing to the analytical limitation mentioned
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K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation 487
above. A significant improvement is provided by life cell
imaging using fluorescent probes. The introduction of the
GSH-specific fluorescent dye monochlorobimane allows
researchers to monitor cellular glutathione levels, changes
of glutathione abundance and cellular transport between
cytosol and vacuole (Meyer et al., 2001; Grzam et al.,
2007). Unfortunately, this approach for plastids is hampered by the lack of glutathione-S-transferase activity that
is necessary to conjugate the dye with glutathione to the
fluorescent form. A major breakthrough was therefore the
development of glutathione redox sensors that consist of
a fusion of glutaredoxin with redox-sensitive GFP (roGFP)
(Gutscher et al., 2008). This probe operates not only in
the cytosol but also in the ER (Birk et al., 2013), mitochondria (Albrecht et al., 2014) and plastids (Maughan et al.,
2010). Within the limits of the redox potential range the
roGFP probe reports the redox potential of the glutathione
pool of a given compartment. Remarkably, the in vivo
­measurement of the glutathione redox state indicates its
almost complete reduction under non-challenged growth
(Meyer et al., 2007). Using this approach the glutathione
pool in Arabidopsis mutants lacking a glutathione transporter in the chloroplast membrane could be visualized
(Maughan et al., 2010). Expression of roGFP in mitochondria or chloroplasts of Arabidopsis revealed that oxidative
shifts in mitochondria stimulate intercellular transport
via plasmodesmata. In a converse manner, chloroplast
thiol oxidation inhibits intercellular transport (Stonebloom et al., 2012).
state feeds back to the committed step of sulfur assimilation via a thiol switch (Figure 3).
A peculiar subcellular distribution of involved enzymes
controls the synthesis of cysteine from assimilatory sulfide.
Cysteine synthesis is accomplished by the enzymes serine
acetyltransferase (SAT) and O-acetylserine (OAS) thiol
lyase via the intermediate O-acetylserine. Both enzymes
are present in the cytosol, plastids and mitochondria and
together form the cysteine synthase complex that acts as
sulfide sensor and regulator [overview in Hell and Wirtz
(2011)]. Enzyme activities of SAT and OAS-TL are unevenly
distributed between the three compartments. Systematic
analysis of null mutants indicates that chloroplasts synthesize little cysteine under control conditions while mitochondria provide the bulk of the precursor OAS and the cytosol
generates most of the cysteine, and that OAS and cysteine
are freely exchangeable between the compartments (Heeg
et al., 2008; Birke et al., 2013). Nevertheless, deletion of the
plastid isoform OASTL-B significantly reduced biomass production by about 25%. The significance of plastid cysteine
synthesis may further increase conditionally.
In contrast, the first step of glutathione synthesis leading
to γ-glutamylcysteine is catalyzed by γ-glutamylcysteine
ligase (GCL) exclusively in the plastids and the second step,
catalyzed by glutathione synthetase (GS), is present in plastids and the cytosol in Arabidopsis (Wachter et al., 2005).
GCL catalyzes the regulatory step and is subject to transcriptional control in response to certain stresses, e.g., imposed
by cadmium and jasmonic acid, but scarcely in response to
H2O2 (Xiang and Oliver, 1998). GCL structure and activity are
Thiol switches in chloroplast
­glutathione homeostasis
The general response of the glutathione pool to oxidative
stress is characterized by an initial change to more oxidized states followed by acclimation based on increased
glutathione concentrations and related enzyme activities,
both leading to enhanced regeneration of glutathione
levels and readjustment of redox state (Tausz et al., 2004).
The initial phase initiates signal transduction via oxidation of protein-thiol relays, whereas the following phase
requires cysteine for glutathione synthesis and NADPH
for reduction of GSSG. Assimilatory reduction of sulfate
and the synthesis of cysteine and glutathione are best
characterized in A. thaliana. Remarkably, the key integrator of external and internal signals for flux control in
sulfate reduction, adenosine 5′-phosphosulfate reductase
(APR) in plastids, is suggested to be redox controlled via
disulfide bridges (Bick et al., 2001). Thus the thiol redox
S S
SO42-
APR
SO32APS
γ-GC CLT
GSH
γ-GC
GS
GSH
GSH
GR1
GSSG
Peroxisome
S S
CSC
H2S
GCL
GS
Cys
γ GC
GSH
GR1
GSSG NTRA
Chloroplast
CSC
HSCys
GSH
GR2
GSSG NTRC
CSC
HSCys
GSH
GR2
GSSG NTRB
Mitochondrium
Figure 3: Subcellular organisation of the glutathione redox hub and
reactions leading to glutathione synthesis.
APR, adenosine-5′-phosphosulfate reductase; APS, adenosine-5′phosphosulfate; CLT, CRT-like transporter; CSC, cysteine synthase
complex; γGC, γ-glutamylcysteine; GCL, γ-glutamylcysteine ligase;
GR, glutathione reductase; GS, glutathione synthetase; NTR,
NADPH-dependent thioredoxin reductase A, B.
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488 K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation
redox sensitive: fully reduced GCL has only little activity while
fully oxidized GCL is very active and gives rise to a higher
apparent molecular weight (Hell and B
­ ergmann, 1990). The
three-dimensional structure reveals that GCL carries two
intramolecular disulfide bridges in some species. One opens
and closes the catalytic center and realizes redox control
in vitro and probably in vivo, the other has structural function and causes an open conformation when reduced (Jez
et al., 2004; Hothorn et al., 2006; Hicks et al., 2007; Gromes
et al., 2008). This intriguing mechanism cannot be generalized due to the variation in GCL cysteine arrangements.
Arabidopsis mutant complementation analyses show that
γ-glutamylcysteine and glutathione are freely exchangeable
across the chloroplasts membranes (­Pasternak et al., 2008;
Lim et al., 2014). This transport is mediated by membrane
proteins with similarity to chloroquine transporters in the
malaria parasite Plasmodium falciparum (chloroquine-like
transporters, CLT) (Maughan et al., 2010). CLT triple mutants
appear to have higher glutathione contents in chloroplasts
than in the cytosol according to roGFP measurements, indicating impaired exchange between both pools. However,
they are vital, suggesting the existence of additional transport systems. Thus, the chloroplast is a quite open system
with respect to glutathione homeostasis. Whether GSSG
can also be exchanged between chloroplast and cytosol is
unclear, however, GR isoforms are known to be present at
both sites as well as in the mitochondria and peroxisomes.
Arabidopsis mutants defective in the dual targeted chloroplast and mitochondrial GR2 are lethal (Tzafrir et al., 2004),
but in the cytosol and mitochondria back-up systems by
NADPH thioredoxin reductases (NTRB, NTRC) are able to
partially replace GR activities (Marty et al., 2009). It should
be noted that GR1 plays a specific role under oxidative stress
and in response to virulent bacteria (Mhamdi et al., 2010).
At least under these conditions NADPH thioredoxin reductases fail to substitute for GR1. Turnover of glutathione, particularly of GSSG, as a player in glutathione homoeostasis in
chloroplasts appears to be unlikely. The reactions that are
able to initiate cleavage of the γ-glutamyl bond are either
catalyzed by γ-glutamyltransferases in the vacuole and at
the outside of the plasmalemma (Martin et al., 2007) or by
a γ-glutamylcyclotransferase in the cytosol (Paulose et al.,
2013).
Balancing reduction and oxidation
defines activity
Effective control of functional activity depends on reversibility, which requires mechanisms of activation and
deactivation (Figure 4). The PQ redox sensing is linked to
the kinases STATE TRANSITION7 (STN7) and STN8 (Samol
et al., 2012). STN7 affects relative activities of photosystem
I and photosystem II by phosphorylating light harvesting
proteins of PSII. STN8 phosphorylates core polypeptides of
PSII and thereby affects thylakoid assembly and the repair
cycle of PSII. PHOTOSYSTEM II CORE PHOSPHATASE
(PBCP) dephosphorylates, e.g., CP43, D1, D2, and PsbH of
PSII proteins and antagonizes STN8, while PPH1/TAP38
phosphatase is the antagonist of STN7 kinase. Likewise
activation by, for example, disulfide reduction, requires
a mechanism for oxidation. While reduction processes
are well described for decades, the oxidation of dithiols
is little understood. Figure 4 presents three thiol switch
mechanisms that interfere with signaling. Thiol peroxidases such as peroxiredoxins and glutathione peroxidases react with peroxides with high affinity. The two
catalytic thiols, the peroxidatic thiol and the resolving
thiol, reduce H2O2 to water, and organic peroxides to the
A
B
PQ
NADPH
STN8
NTRC
PsbH
PsbH
Prx
P
PBCP
Phosphorylation/Dephosphorylation
C
TP
Prx
S
H2O2
TP
SOH
Prx
SH
SH
Proximity-based oxidation
SH
SH
SH
SH
NADPH
ROOH/
H2O2
NTRC
Prx
NTRC
S
SH
Prx
S
ROOH/H2O2
ROS mediated direct oxidation
D
NADPH
S
TP
S
S
TP
S
S
SH
SH
Competition/reversibility
Figure 4: Mechanisms of reversible thiol switching in chloroplasts.
(A) The plastoquinone (PQ) redox state activates the state transition kinases STN7 and STN8. STN8 phosphorylates, for example,
the thylakoid protein PsbH. Dephosphorylation is catalyzed by the
photosystem II core phosphatase PBCP. (B) Adjustment of peroxiredoxin (Prx) redox state by oxidation with H2O2 or organic peroxides
and reduction by NTRC or, not shown, other thiol reductants. (C)
Thiol/disulfide control of a target protein (TP) by proximity based
oxidation through Prx and reduction by NTRC or thioredoxin. Here,
the sulfenic acid derivative of CysP of the peroxiredoxin oxidizes
the thiol of the protein in near proximity. The sulfenic acid on the
protein reacts with a second thiol to form a disulfide. (D) Oxidation
and reduction of a TP by equilibration with the redox transmitter,
e.g., NTRC, whose redox state in turn is controlled by NADPH and
drainage of electrons into the Prx pathway.
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K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation 489
corresponding alcohols (Herbette et al., 2007; Dietz, 2011).
NTRC re-reduces the 2-cysteine peroxiredoxin (2-CysPrx),
the predominant peroxiredoxin in chloroplasts (Pulido
et al., 2010). Thus the system H2O2/2-CysPrx/NTRC represents an example of direct oxidation of thiol switches
by peroxide and reduction by Trx-linked mechanisms. In
dependence on its redox state and conformational state,
2-CysPrx functions as thiol peroxidase, chaperone, regulatory interactor or proximity based oxidase (König et al.,
2013) (Figure 4B). Redox proteomics allows for identification of stromal proteins with high sensitivity to H2O2 in vitro
(Muthuramalingam et al., 2013). The proof of direct oxidation by H2O2 in vivo will be difficult to realize. Reduction of
target proteins by thioredoxins is the common principle
of thiol regulation. Oxidation may be achieved by proximity based oxidation as suggested by Gutscher et al. (2009).
The sulfenic acid intermediate or the disulfide form could
oxidize the reduced target protein (Figure 4C). In this
scenario, the redox state of the target is adjusted by Trxdependent reduction and reoxidation by proximity based
mechanisms. Another pathway could employ the reversibility of the thiol/disulfide exchange between target proteins and thioredoxin (Figure 4D). Thus if 2-CysPrx as ROS
sensor drains electrons from NTRC or Trx-x, these oxidized
transmitters could in turn oxidize other interacting target
proteins. In addition to peroxiredoxins, glutathione peroxidases also function as Trx-linked thiol peroxidases and
might function as redox sensors (Rodriguez Milla et al.,
2003). Glutathione peroxidase (Gpx) 1 and 7 localize to
the chloroplast in A. thaliana (Chang et al., 2009). In addition to a role in antioxidant defense, results from plants
with manipulated amounts of Gpx1 and Gpx7 indicate that
chloroplast Gpxs participate in signaling and optimizing
chloroplast and extrachloroplast metabolism during high
light acclimation (Chang et al., 2009). Both, Gpx1 and
Gpx7 were shown to be important for hormone homeostasis in lateral root formation (Passaia et al., 2014). Thus
plastidic Prx and Gpx are strong candidates for controlling
reversible thiol switches in plastids similar to the report
from mammalian redox relay formed from the transcription factor STAT1 and Prdx2 (Sobotta et al., 2015).
Thiol switches in oligomeric
­assemblies and microdomains
The number of described thiol switches in chloroplasts
increases rapidly. Interestingly many of the redox regulatory agents are associated with specific macromolecular
assemblies or suborganellar structures such as 2-CysPrx
with PSII, PrxQ with thylakoid stacks or Trx-z with transcriptionally active chromosomes (TACs) (Arsova et al.,
2010). The specific localization of these components indicates functions in defined molecular environment, despite
the fact that the strong phenotype of Trx-z-­
deficient
mutants can be complemented with thiol-mutated
Trx-z excluding an exclusive redox function of Trx-z
(­Wimmelbach and Börnke, 2014). Significant heterogeneity in terms of spreading can be expected from different
ROS signals. Important factors are the rate of ROS generation, ROS reactivity and half life time and activity of the
antioxidant defense system. Singlet oxygen likely acts in
the thylakoid membrane and initiates oxylipin signaling,
which in turn activates Cys synthesis by oxophytodienoic
acid (OPDA) binding to cyclophilin Cyp20-3 (Park et al.,
2013). The Cyp20-3/OPDA complex binds the cysteine synthase complex consisting of OAS thiol lyase and serine
acetyltransferase and is suggested to stimulate OAS synthesis as precursor of cysteine synthesis. Superoxide and
H2O2 can diffuse, but their concentration is controlled by
efficient antioxidant defense systems (Figure 5). Thus, if
thylakoid-bound superoxide dismutases, ascorbate peroxidases and thiol peroxidases are active, O2·- and H2O2 only
Efficient
antioxidant
defence
Local
signaling
initiation
Fd
PQ
PQ
Thioldependent
regulation
Protein
kinase
Thylakoid lumen
Lipid
signaling
↑O2
PQ
PQ
PQ
O2-
Weak
antioxidant
defence
SH
Sensor
SH
SH
H2O2
SOH
Sensor
S
S
ROSrelated
signaling
Figure 5: Sources and gradients in redox stimulus propagation and
signaling.
The schematics depict a chloroplast with a stack of thylakoid membranes as site of photosynthetic electron transport. ROS gradients
are labeled as red areas and show singlet oxygen initiating lipid
signaling, a site of efficient antioxidant defense (upper part) where
ferredoxin- (Fd) and plastoquinone (PQ)-dependent redox signaling affect thiol regulation and protein kinase activity. A site of
weakened antioxidant defense (lower part) allows for spreading of
ROS and reaction with ROS sensors which then trigger ROS-related
signaling.
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490 K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation
can act locally similar as discussed for retrograde signaling by Baier and Dietz (2005). If the antioxidant defense is
weakened, then ROS signals may spread and even leave
the chloroplast. It has been proposed that the antioxidant
activity is regulated. Such mechanisms would allow for
control of local signaling in macromolecular assemblies
on the scale of nanometers vs. more distant signaling
on the submicrometer to micrometer scale by diffusion
(Heyno et al., 2014). Buffering of ROS and redox disequilibria is not only achieved by the enzymatic and non-enzymatic antioxidants, but also by the huge concentration of
protein thiols, which exceeds the glutathione pool more
than 10-fold (Muthuramalingam et al., 2013). Ribulose1,5-bisphosphate carboxylase/oxygenase is the predominant protein in the stroma with estimated concentrations
of 0.5 mm. Considering the hexadecameric structure with
eight large (9 Cys) and eight small subunits (4 Cys) the
potential contribution of RubisCO Cys amounts to 52 mm
(Muthuramalingam et al., 2013). Many RubisCO Cys have
been identified as targets of posttranslational modifications with effects on activity and turnover (Moreno et al.,
2008).
Redox control of chloroplast
pathways and activities
Tetrapyrrole biosynthesis, chloroplast transcription and
translation may serve as three examples where knowledge on redox regulation and thiol switches in chloroplasts has advanced tremendously in recent years. NTRC
has emerged as a central player in chloroplast thiol redox
homeostasis (Toivola et al., 2013). NTRC contains the functional domain of a thioredoxin reductase and a thioredoxin
domain. Genetic NTRC:GFP fusions distribute equally in
the chloroplast (Kirchsteiger et al., 2012). ntrc-knock out
A. thaliana plants grow slowly and display a chlorotic
phenotype. Complementation with an NTRC containing
the functional thioredoxin reductase domain but inactive
Trx domain restored growth indicating that the TR domain
likely interacts with other chloroplast Trx (Toivola et al.,
2013). NTRC controls components of tetrapyrrole biosynthesis (Richter et al., 2013). Detailed analysis of metabolite
levels and enzyme activities of tetrapyrrole biosynthesis
in ntrc lines provides evidence that NTRC controls the
activity of glutamyl-transfer RNA reductase 1 and MgP
methyltransferase by thiol switching (Richter et al.,
2013). Additional steps of the tetrapyrrole pathway like
Glu-1-semialdehyde aminotransferase (GSAT) or 5-aminolevulinic acid dehydratase (ALAD) are suggested to be
under control of the ferredoxin-­thioredoxin pathway (see
review by Richter and Grimm, 2013). The precise mechanisms including involved thiol switches still need to be
investigated in detail.
Transcriptionally active chromosomes (TAC) represent DNA-protein assemblies of high complexity with
more than 30 different constituents including RNA polymerase (Pfalz et al., 2006). Some components are linked to
redox and ROS such as Fe superoxide dismutase 3 (FSD3)
and possibly Trx-z as still has to be shown (Arsova et al.,
2010; see above). Recently, AtECB1/MRL7, was identified
as another component of the TAC complex. It possesses
a typical thioredoxin protein fold and exhibits activity of
disulfide reductase. The albino phenotype of ecb1-knock
out plants indicates its function in plastid gene expression
and chloroplast biogenesis (Yua et al., 2014). The mutant
plants lack immunodetectable amounts of photosynthetic proteins such as LSU of ribulose-1,5-bisphosphate
­carboxylase/oxygenase, PsaD, PetC and PsbA. Reliable
molecular interaction of AtECB1 with Trx-z and FSD3 were
taken as circumstantial evidence that AtECB1 might regulate plastid transcription by redox-related mechanisms
(Yua et al., 2014). WHIRLY1 and possibly WHIRLY3 (WHY1,
WHY3) are components of the plastid nucleoid and were
suggested to function as major scaffold for nucleoid
assembly (Krupinska et al., 2014). WHY1 and WHY3 have
conserved Cys residues that could regulate WHY-function.
WHY3 was identified as redox-sensitive target in a redox
proteomic approach (Ströher and Dietz, 2008). Interestingly WHY 1 is unique because it is the only transcription
factor described so far that is dually localized to the plastids and nucleus and thus may serve as retrograde signal.
It will be interesting to determine the significance of redox
regulation for WHIRLY distribution and function.
Redox regulation of chloroplast translation allows for
rapid adjustment of protein synthesis to the demand for
their assembly in photosynthetic complexes and of ribulose1,5-bisphosphate carboxylase/oxygenase (­
Marín-Navarro
et al., 2007). In yeast extracts prepared for in vitro translation studies, addition of thioredoxin or glutaredoxin in
combination with dithiothreitol enhanced synthesis of
luciferase mRNA (Jun et al., 2009). Likewise translation of
PsbA-mRNA in illuminated chloroplasts was stimulated by
light. The light stimulus activated translation through the
ferredoxin-thioredoxin system (Trebitsh and Danon, 2001).
Recently, the protein disulfide isomerase AtPDI6 could be
localized to the chloroplast (­Wittenberg et al., 2014). Atpdi6plants when exposed to a 10-fold light increase showed less
photoinhibition and higher rates of D1-protein turnover.
The authors suggest that AtPDI6 may act as attenuator of
translation, controlling D1 synthesis in response to light
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K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation 491
and redox cues (Wittenberg et al., 2014). Thus mounting
evidence ties translation into the redox regulatory network
of the chloroplast.
Conclusions
Thiol switches are fundamental part of cell redox regulation. The photosynthesizing chloroplast experiences significant redox changes. Considering the structure of the
redox regulatory thiol-network consisting of redox input
elements, redox transmitters, redox targets and redox
sensors the following scenario needs to be considered:
metabolism including PET chain feeds electrons via the
redox input elements to the targets. Thus electron input
by increasing electron pressure reduces targets. Conversely, ROS act as final electron acceptors (Dietz, 2008).
The balance between electron input and electron drainage defines the redox state of the targets and controls
metabolism, transcription, translation or export. Both,
decreasing the reductive pressure or increasing the oxidative drainage of electrons will have similar effects. As
described in this review, only part of redox regulation and
thiol switching occurs via the bulk phase. As alternative
mechanism, redox information is exploited in microdomains and supramolecular assemblies. To fully assess
the significance of the thiol/disulfide redox proteome for
chloroplast function, much additional ex vivo work will
have to link environmental conditions and metabolic state
to specific patterns of the redox proteome.
Acknowledgments: This work was funded by the Deutsche
Forschungsgemeinschaft (DFG), in particular within the
framework of the Schwerpunktprogramm SPP 1710.
References
Albrecht, S.C., Sobotta, M.C., Bausewein, D., Aller, I., Hell, R., Dick,
T.P., and Meyer, A.J. (2014). Redesign of genetically encoded
biosensors for monitoring mitochondrial redox status in a
broad range of model eukaryotes. J. Biomolecular Screening
19, 379–386.
Alsharafa, K., Vogel, M.O., Oelze, M.L., Moore, M., Stingl, N., König,
K., Friedman, H., Mueller, M.J., and Dietz, K.J. (2014). Kinetics
of retrograde signalling initiation in the high light response of
Arabidopsis thaliana. Philos. Trans. R. Soc. Lond. B Biol. Sci.
369, 20130424.
Arsova, B., Hoja, U., Wimmelbacher, M., Greiner, E., Üstün, S.,
Melzer, M., Petersen, K., Lein, W., and Börnkeb, F. (2010). Plastidial thioredoxin z interacts with two fructokinase-like proteins in a thiol-dependent manner: evidence for an essential
role in chloroplast development in Arabidopsis and Nicotiana
benthamiana. Plant Cell 22, 1498–1515.
Baier, M. and Dietz, K.J. (2005). Chloroplasts as source and target
of cellular redox regulation: a discussion on chloroplast redox
signals in the context of plant physiology. J. Exp. Bot. 56,
1449–1462.
Ball, L., Accotto, G.P., Bechtold, U., Creissen, G., Funck, D., Jimenez,
A., Kular, B., Leyland, N., Mejia-Carranza, J., Reynolds, H., et al.
(2004). Evidence for a direct link between glutathione biosynthesis and stress defense gene expression in Arabidopsis.
Plant Cell 16, 2448–2462.
Bergmann, L. and Rennenberg, H. (1993). Glutathione metabolism
in plants. In: Sulfur Nutrition and Assimilation in Higher Plants.
Regulatory, Agricultural and Environmental Aspects. L.J. De
Kok, I. Stulen, H. Rennenberg, C. Brunold, and W.E. Rauser,
eds. (The Hague: SPB Academic Publishing), pp. 102–123.
Bick, J.A., Setterdahl, A.T., Knaff, D.B., Chen, Y., Pitcher, L.H.,
­Zilinskas, B.A., and Leustek, T. (2001). Regulation of the
plant-type 5′-adenylyl sulfate reductase by oxidative stress.
Biochemistry 40, 9040–9048.
Birk, J., Meyer, M., Aller, I., Hansen, H.G., Odermatt, A., Dick, T.P.,
Meyer, A.J, and Appenzeller-Herzog, C. (2013). Endoplasmic
reticulum: reduced and oxidized glutathione revisited. J. Cell
Sci. 126, 1604–1617.
Birke, H., Heeg, C., Wirtz, M., and Hell, R. (2013). Successful
fertilization requires the presence of at least one major
O-acetylserine(thiol)lyase for cysteine synthesis in pollen of
Arabidopsis. Plant Physiol. 163, 959–972.
Blanco, N.E., Ceccoli, R.D., Vía, M.V., Voss, I., Segretin, M.E., BravoAlmonacid, F.F., Melzer, M., Hajirezaei, M.R., Scheibe, R., and
Hanke, G.T. (2013). Expression of the minor isoform pea ferredoxin in tobacco alters photosynthetic electron partitioning
and enhances cyclic electron flow. Plant Physiol. 161, 866–879.
Chang, C.C., Slesak, I., Jordá, L., Sotnikov, A., Melzer, M., Miszalski,
Z., Mullineaux, P.M., Parker, J.E., Karpinska, B., and Karpinski,
S. (2009). Arabidopsis chloroplastic glutathione peroxidases
play a role in cross talk between photooxidative stress and
immune responses. Plant Physiol. 150, 670–683.
de Lamotte-Guery, F., Miginiac-Maslow, M., Decottignies, P., Stein,
M., Minard, P., and Jacquot, J.P. (1991). Mutation of a negatively
charged amino acid in thioredoxin modifies its reactivity with
chloroplastic enzymes. Eur. J. Biochem. 196, 287–294.
Dietz, K.J. (2008). Redox signal integration: from stimulus to networks and genes. Physiol. Plant 133, 459–468.
Dietz, K.J. (2011). Peroxiredoxins in plants and cyanobacteria.
­Antioxid. Redox Signal. 15, 1129–1159.
Gromes, R., Hothorn, M., Lenherr, E.D., Rybin, V., Scheffzek, K.,
and Rausch, T. (2008). The redox switch of γ-glutamylcysteine
ligase via a reversible monomer-dimer transition is a mechanism unique to plants. Plant J. 54, 1063–1075.
Grzam, A., Martin, M., Hell, R., and Meyer, A. (2007). γ-Glutamyl
transpeptidase GGT4 initiates vacuolar degradation of
glutathione S-conjugates in Arabidopsis. FEBS Lett. 581,
3131–3138.
Gutscher, M., Pauleau, A., Marty, L., Brach, T., Wabnitz, G.,
­Samstag, Y., Meyer, A., and Dick, T. (2008). Real-time imaging
of the intracellular glutathione redox potential. Nat. Methods
5, 553–559.
Gutscher, M., Sobotta, M.C., Wabnitz, G.H., Ballikaya, S., Meyer,
A.J., Samstag, Y., and Dick, T.P. (2009). Proximity-based protein
Unauthenticated
Download Date | 7/31/17 9:56 PM
492 K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation
thiol oxidation by H2O2-scavenging peroxidases. J. Biol. Chem.
284, 31532–31540.
Heber, U.W. and Santarius, K.A. (1965). Compartmentation and
reduction of pyridine nucleotides in relation to photosynthesis.
Biochim. Biophys. Acta 109, 390–408.
Heeg, C., Kruse, C., Jost, R., Gutensohn, M., Ruppert, T., Wirtz,
M., and Hell, R. (2008). Analysis of the Arabidopsis
O-acetylserine(thiol)lyase gene family demonstrates compartment-specific differences in the regulation of cysteine synthesis. Plant Cell 20, 168–185.
Hell, R. and Bergmann, L. (1990). γ-Glutamylcysteine synthetase in
higher plants: catalytic properties and subcellular localization.
Planta 180, 603–612.
Hell, R. and Kruse, C. (2007). Sulfur in biotic interactions of plants.
In: Sulfur in Plants: An Ecological Perspective, M.J. Kok and J.D.
Hal, eds. (Dordrecht, The Netherlands: Springer), pp. 197–224.
Hell, R. and Wirtz, M. (2011). Molecular biology, biochemistry and
cellular physiology of cysteine metabolism in Arabidopsis
thaliana. The Arabidopsis Book 9, e0154.
Herbette, S., Roeckel-Drevet, P., and Drevet, J.R. (2007). Selenoindependent glutathione peroxidases. More than simple
antioxidant scavengers. FEBS J. 274, 2163–2180.
Heyno, E., Innocenti, G., Lemaire, S.D., Issakidis-Bourguet, E.,
and Krieger-Liszkay, A. (2014). Putative role of the malate
valve enzyme NADP-malate dehydrogenase in H2O2 signalling
in Arabidopsis. Philos. Trans. R. Soc. Lond. B Biol. Sci. 369,
2013022.
Hicks, L.M., Cahoon, R.E., Bonner, E.R., Rivard, R.S., Sheffield, J.,
and Jez, J.M. (2007). Thiol-based regulation of redox-active
glutamate-cysteine ligase from Arabidopsis thaliana. Plant Cell
19, 2653–2661.
Hothorn, M., Wachter, A., Gromes, R., Stuwe, T., Rausch, T., and
Scheffzek, K. (2006). Structural basis for the redox control of
plant glutamate cysteine ligase. J. Biol. Chem. 281, 27557–
27565.
Jun, K.O., Song, C.H., Kim, Y.B., An, J., Oh, J.H., and Choi, S.K.
(2009). Activation of translation via reduction by thioredoxinthioredoxin reductase in Saccharomyces cerevisiae. FEBS Lett.
583, 2804–2810.
Jez, J.M., Cahoon, R.E., and Chen, S. (2004). Arabidopsis thaliana
glutamate-cysteine ligase: functional properties, kinetic
mechanism, and regulation of activity. J. Biol. Chem. 279,
33463–33470.
Kirchsteiger, K., Ferrández, J., Pascual, M.B., González, M., and
Cejudo, F.J. (2012). NADPH thioredoxin reductase C is localized
in plastids of photosynthetic and nonphotosynthetic tissues
and is involved in lateral root formation in Arabidopsis. Plant
Cell 24, 1534–1548.
Klapheck, S., Latus, C., and Bergmann, L. (1987). Localization of
glutathione synthetase and distribution of glutathione in leaf
cells of Pisum sativum L. J. Plant Physiol. 131, 123–131.
Kobayashi, Y., Köster, S., and Heber, U. (1982). Light-scattering,
chlorophyll fluorescence and state of the adenylate system in
illuminated spinach leaves. Biochim. Biophys. Acta 682, 44–54.
König, J., Muthuramalingam, M., and Dietz, K.J. (2012). Mechanisms
and dynamics in the thiol/disulfide redox regulatory network:
transmitters, sensors and targets. Curr. Opin. Plant Biol. 15,
261–268.
König, J., Galliardt, H., Jütte, P., Schäper, S., Dittmann, L., and Dietz,
K.J. (2013). The conformational bases for the two functionali-
ties of 2-cysteine peroxiredoxins as peroxidase and chaperone.
J. Exp. Bot. 64, 3483–3497.
Krupinska, K., Oetke, S., Desel, C., Mulisch, M., Schäfer, A.,
­Hollmann, J., Kumlehn, J., and Hensel, G. (2014). WHIRLY1 is a
major organizer of chloroplast nucleoids. Front. Plant Sci. 5, 432.
Krüger, S., Niehl, A., Martin, M.C.L., Steinhauser, D., Donath, A.,
Hildebrandt, T., Romero, L.C., Hoefgen, R., Gotor, C., and
Hesse, H. (2009). Analysis of cytosolic and plastidic serine
acetyltransferase mutants and subcellular metabolite distributions suggests interplay of the cellular compartments for
cysteine biosynthesis in Arabidopis. Plant Cell Environ. 32,
349–367.
Laisk, A., Siebke, K., Gerst, U., Eichelmann, H., Oja, V., and Heber,
U. (1991). Oscillations in photosynthesis are initiated and supported by imbalances in the supply of ATP and NADPH to the
Calvin cycle. Planta 185, 554–562.
Lim, B., Pasternak, M., Meyer, A.J., and Cobbett, C.S. (2014).
Restricting glutamylcysteine synthetase activity to the cytosol
or glutathione biosynthesis to the plastid is sufficient for
normal plant development and stress tolerance. Plant Biol. 16,
58–67.
Marín-Navarro, J., Manuell, A.L., Wu, J.P., and Mayfield, S. (2007).
Chloroplast translation regulation. Photosynth. Res. 94,
359–374.
Martin, M.N., Saladores, P.H., Lambert, E., Hudson, A.O., and
­Leustek, T. (2007). Localization of members of the γ-glutamyl
transpeptidase family identifies sites of glutathione and glutathione S-conjugate hydrolysis. Plant Physiol. 144, 1715–1732.
Marty, L., Siala, W., Schwarzlander, M., Fricker, M.D., Wirtz, M.,
Sweetlove, L.J., Meyer, Y., Meyer, A.J., Reichheld, J.-P., and Hell,
R. (2009). The NADPH-dependent thioredoxin system constitutes a functional backup for cytosolic glutathione reductase in
Arabidopsis. Proc. Natl. Acad. Sci. USA 106, 9109–9114.
Maughan, S.C., Pasternak, M., Cairns, N., Kiddle, G., Brach, T.,
Jarvis, R., Haas, F., Nieuwland, J., Lim, B., Muller, C., et al.
(2010). Plant homologs of the Plasmodium falciparum
chloroquine-resistance transporter, PfCRT, are required for glutathione homeostasis and stress responses. Proc. Natl. Acad.
Sci. USA 107, 2331–2336.
May, M., Vernoux, T., Leaver, C., Van Montagu, M., and Inze, D.
(1998). Glutathione homeostasis in plants: implications for
environmental sensing and plant development. J. Exp. Bot. 49,
649–667.
Meyer, A.J. and Rausch, T. (2008). Biosynthesis, compartmentation and cellular functions of glutathione in plant cells. In:
Sulfur Metabolism in Phototrophic Organisms, R. Hell, C. Dahl,
D.B. Knaff and T. Leustek, eds. (Dordrecht, The Netherlands:
Springer), pp. 161–184.
Meyer, A.J., May, M.J., and Fricker, M. (2001). Quantitative in vivo
measurement of glutathione in Arabidopsis cells. Plant J. 27,
67–78.
Meyer, A.J., Brach, T., Marty, L., Kreye, S., Rouhier, N., Jacquot, J.-P,
and Hell, R. (2007). Redox-sensitive GFP in Arabidopsis thaliana is a quantitative biosensor for the redox potential of the
cellular glutathione redox buffer. Plant J. 52, 973–986.
Mhamdi, A., Hager, J., Chaouch, S., Queval, G., Han, Y., Taconnat, L.,
Saindrenan, P., Gouia, H., Issakidis-Bourguet, E., Renou, J.P.,
et al. (2010). Arabidopsis GLUTATHIONE REDUCTASE1 plays a
crucial role in leaf responses to intracellular hydrogen peroxide
and in ensuring appropriate gene expression through both
Unauthenticated
Download Date | 7/31/17 9:56 PM
K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation 493
salicylic acid and jasmonic acid signaling pathways. Plant
Physiol. 153, 1144–1160.
Miyake, C. (2010). Alternative electron flows (water-water cycle and
cyclic electron flow around PSI) in photosynthesis: molecular
mechanisms and physiological functions. Plant Cell Physiol.
51, 1951–1963.
Moreno, J., Garcia-Murria, M.J., and Marin-Navarro, J. (2008). Redox
modulation of Rubisco conformation and activity through its
cysteine residues. J. Exp. Bot. 59, 1605–1614.
Muthuramalingam, M., Matros, A., Scheibe, R., Mock, H.P., and
Dietz, K.J. (2013). The hydrogen peroxide-sensitive proteome of
the chloroplast in vitro and in vivo. Front. Plant Sci. 4, 54.
Noctor, G. and Foyer, C.H. (1998). Ascorbate and glutathione: keeping active oxygen under control. Annu. Rev. Plant Physiol. Plant
Mol. Biol. 49, 249–279.
Noctor, G., Queval, G., Mhamdi, A., Chaouch, S., and Foyer, C.H.
(2011). Glutathione. The Arabidopsis Book, e0142.
Noctor, G., Mhamdi, A., Chaouch, S., Han, Y., Neukermans, J.,
Marquez-Garcia, B., Queval, G., and Foyer, C.H. (2012). Glutathione in plants: an integrated overview. Plant Cell Environ.
35, 454–484.
Park, S.W., Li, W., Viehhauser, A., He, B., Kim, S., Nilsson, A.K.,
Andersson, M.X., Kittle, J.D., Ambavaram, M.M., Luan, S., et al.
(2013). Cyclophilin 20-3 relays a 12-oxo-phytodienoic acid
signal during stress responsive regulation of cellular redox
homeostasis. Proc. Natl. Acad. Sci. USA 110, 9559–9564.
Passaia, G., Queval, G., Bai, J., Margis-Pinheiro, M., and Foyer, C.H.
(2014). The effects of redox controls mediated by glutathione
peroxidases on root architecture in Arabidopsis thaliana. J.
Exp. Bot. 65, 1403–1413.
Pasternak, M., Lim, B., Wirtz, M., Hell, R., Cobbett, C.S., and Meyer,
A.J. (2008). Restricting glutathione biosynthesis to the cytosol is
sufficient for normal plant development. Plant J. 53, 999–1012.
Paulose, B., Chhikara, S., Coomey, J., Jung, H.I., Vatamaniuk, O., and
Dhankher, O.P. (2013). A γ-glutamyl cyclotransferase protects
Arabidopsis plants from heavy metal toxicity by recycling
glutamate to maintain glutathione homeostasis. Plant Cell 25,
4580–4595.
Peltier, J.B., Cai, Y., Sun, Q., Zabrouskov, V., Giacomelli, L., Rudella,
A., Ytterberg, A.J., Rutschow, H., and van Wijk, K.J. (2006). The
oligomeric stromal proteome of Arabidopsis thaliana chloroplasts. Mol. Cell. Proteomics 5, 114–133.
Pfalz, J., Liere, K., Kandlbinder, A., Dietz, K.J. and Oelmüller, R.
(2006). pTAC2, -6, and -12 are components of the transcriptionally active plastid chromosome that are required for plastid
gene expression. Plant Cell 18, 176–197.
Pulido, P., Spínola, M.C., Kirchsteiger, K., Guinea, M., Pascual,
M.B., Sahrawy, M., Sandalio, L.M., Dietz, K.J., González, M.,
and Cejudo, F.J. (2010). Functional analysis of the pathways for
2-Cys peroxiredoxin reduction in Arabidopsis thaliana chloroplasts. J. Exp. Bot. 61, 4043–4054.
Puthiyaveetil, S., Ibrahim, I.M., and Allen, J.F. (2012). Oxidationreduction signalling components in regulatory pathways of
state transitions and photosystem stoichiometry adjustment in
chloroplasts. Plant Cell Environ. 35, 347–359.
Rausch, T. and Wachter, A. (2005). Sulfur metabolism: a versatile
platform for launching defence operations. Trends Plant Sci.
10, 503–509.
Richter A.S. and Grimm, B. (2013). Thiol-based redox control of
enzymes involved in the tetrapyrrole biosynthesis pathway in
plants. Front. Plant Sci. 4, 371.
Richter, A.S., Peter, E., Rothbart, M., Schlicke, H., Toivola, J.,
Rintamäki, E., and Grimm, B. (2013). Posttranslational influence of NADPH-dependent thioredoxin reductase C on enzymes
in tetrapyrrole synthesis. Plant Physiol. 162, 63–73.
Rochaix, J.D. (2013). Redox regulation of thylakoid protein kinases
and photosynthetic gene expression. Antioxid. Redox Signal.
18, 2184–2201.
Rodriguez Milla, M.A., Maurer, A., Rodriguez Huete, A., and
­Gustafson, J.P. (2003). Glutathione peroxidase genes in
Arabidopsis are ubiquitous and regulated by abiotic stresses
through diverse signaling pathways. Plant J. 36, 602–615.
Samol, I., Shapiguzov, A., Ingelsson, B., Fucile, G., Crèvecoeur,
M., Vener, A.V., Rochaix, J.D., and Goldschmidt-Clermont, M.
(2012). Identification of a photosystem II phosphatase involved
in light acclimation in Arabidopsis. Plant Cell 24, 2596–2609.
Scheibe, R. and Dietz, K.J. (2012). Redox-network for flexible adjustment of cellular metabolism in photoautotrophic cells. Plant
Cell Environ. 35, 202–216.
Schürmann, P. and Wolosiuk, R.A. (1978). Studies on the regulatory properties of chloroplast fructose-1,6-bisphosphatase.
Biochim. Biophys. Acta 522, 130–138.
Shikanai, T. (2014). Central role of cyclic electron transport around
photosystem I in the regulation of photosynthesis. Curr. Opin.
Biotech. 26, 25–30.
Sivak, M., Dietz, K.J., Heber, U., and Walker, D.A. (1985). The
relationship between light scattering and chlorophyll a
fluorescence during oscillations in photosynthetic carbon
assimilation. Arch. Biochem. Biophys. 237, 513–519.
Sobotta, M.C., Liou, W., Stöcker, S., Talwar, D., Oehler, M.,
Ruppert, T., Scharf, A.N., and Dick, T.P. (2015). Peroxiredoxin-2
and STAT3 form a redox relay for H2O2 signaling. Nat. Chem.
Biol. 11, 64–70.
Stonebloom, S., Brunkard, J.O., Cheung, A.C., Jiang, K., Feldman,
L., and Zambryski, P. (2012). Redox states of plastids and
mitochondria differentially regulate intercellular transport via
plasmodesmata. Plant Physiol. 158, 190–199.
Ströher, E. and Dietz, K.J. (2008). The dynamic thiol-disulphide
redox proteome of the Arabidopsis thaliana chloroplast as
revealed by differential electrophoretic mobility. Physiol. Plant.
133, 566–583.
Takizawa, K., Cruz, J.A., Kanazawa, A., and Kramer, D.M.
(2007). The thylakoid proton motive force in vivo.
­Quantitative, non-invasive probes, energetics, and
regulatory consequences of light-induced pmf. Biochim.
Biophys. Acta 1767, 1233–1244.
Tausz, M., Sircelj, H., and Grill, D. (2004). The glutathione system
as a stress marker in plant ecophysiology: is a stress-response
concept valid? J. Exp. Bot. 55, 1955–1962.
Toivola, J., Nikkanen, L., Dahlström, K.M., Salminen, T.A., Lepistö,
A., Vignols, H.F., and Rintamäki, E. (2013). Overexpression
of chloroplast NADPH-dependent thioredoxin reductase in
Arabidopsis enhances leaf growth and elucidates in vivo
function of reductase and thioredoxin domains. Front. Plant
Sci. 4, 389.
Trebitsh, T. and Danon, A. (2001). Translation of chloroplast psbA
mRNA is regulated by signals initiated by both photosystems II
and I. Proc. Natl. Acad. Sci. USA 98, 12289–12294.
Tzafrir, I., Pena-Muralla, R., Dickerman, A., Berg, M., Rogers, R.,
Hutchens, S., Sweeney, T.C., McElver, J., Aux, G., Patton, D.,
et al. (2004). Identification of genes required for embryo development in Arabidopsis. Plant Physiol. 135, 1206–1220.
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494 K.-J. Dietz and R. Hell: Thiol switches in chloroplast redox regulation
Wachter, A., Wolf, S., Steininger, H., Bogs, J., and Rausch, T. (2005).
Differential targeting of GSH1 and GSH2 is achieved by multiple
transcription initiation: implications for the compartmentation of
glutathione biosynthesis in the Brassicaceae. Plant J. 41, 15–30.
Walker, D.A. (1992). Concerning oscillations. Photosynth. Res. 34,
387–395.
Wimmelbacher, M. and Börnke, F. (2014). Redox activity of thioredoxin z and fructokinase-like protein 1 is dispensable for
autotrophic growth of Arabidopsis thaliana. J. Exp. Bot. 65,
2405–2413.
Wittenberg, G., Levitan, A., Klein, T., Dangoor, I., Keren, N., and
Danon, A. (2014). Knockdown of the Arabidopsis thaliana chloroplast protein disulfide isomerase 6 results in reduced levels
of photoinhibition and increased D1 synthesis in high light.
Plant J. 78, 1003–1013.
Xiang, C. and Oliver, D.J. (1998). Glutathione metabolic genes
coordinately respond to heavy metals and jasmonic acid in
Arabidopsis. Plant Cell 10, 1539–1550.
Yoshida, K., Matsuoka, Y., Hara, S., Konno, H., and Hisabori, T.
(2014). Distinct redox behaviors of chloroplast thiol enzymes
and their relationships with photosynthetic electron transport
in Arabidopsis thaliana. Plant Cell Physiol. 55, 1415–1425.
Yua, Q.B., Ma, Q., Kong, M.M., Zhao, T.T., Zhang, X.L., Zhou, Q.,
Huang, C., Chong, K., and Yang, Z.N. (2014). AtECB1/MRL7, a
thioredoxin-like fold protein with disulfide reductase activity,
regulates chloroplast gene expression and chloroplast biogenesis in Arabidopsis thaliana. Mol. Plant 7, 206–217.
Zaffagnini, M., Bedhomme, M., Lemaire, S.D., and Trost, P. (2012).
The emerging roles of protein glutathionylation in chloroplasts. Plant Sci. 185–186, 86–96.
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