University of Zurich
Zurich Open Repository and Archive
Winterthurerstr. 190
CH-8057 Zurich
http://www.zora.uzh.ch
Year: 2009
Stay-green regulates chlorophyll and chlorophyll-binding protein
degradation during senescence
Hörtensteiner, S
Hörtensteiner, S (2009). Stay-green regulates chlorophyll and chlorophyll-binding protein degradation during
senescence. Trends in Plant Science, 14(3):155-162.
Postprint available at:
http://www.zora.uzh.ch
Posted at the Zurich Open Repository and Archive, University of Zurich.
http://www.zora.uzh.ch
Originally published at:
Trends in Plant Science 2009, 14(3):155-162.
Stay-green regulates chlorophyll and chlorophyll-binding protein
degradation during senescence
Abstract
Stay-green mutants are delayed in leaf senescence and have been identified from different plant species,
including many crops. Functional stay-greens have the potential to increase plant productivity. In
cosmetic stay-greens, however, retention of chlorophyll during senescence is uncoupled from a decline
of photosynthetic capacity in these mutants. For many cosmetic stay-green mutants, including Gregor
Mendel's famous green cotyledon pea variety, molecular defects were recently identified in orthologous
stay-green genes. Stay-green genes encode members of a new family of chloroplast-located proteins,
which are likely to function in dismantling of photosynthetic chlorophyll-apoprotein complexes. Their
activity is considered as a prerequisite for both chlorophyll and apoprotein degradation during
senescence.
3
Stay-green regulates chlorophyll
and chlorophyll-binding protein
degradation during senescence
4
Stefan Hörtensteiner
5
6
Zurich-Basel Plant Science Center, Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland
Corresponding author: Hörtensteiner, S. ([email protected]).
57 breakdown, but recent data indicate that SGR is not
Stay-green mutants are delayed in leaf senescence and
58 directly involved in a chl catabolic step; instead, it is
have been identified from different plant species,
59 required for the dismantling of photosynthetic chl–
including many crops. Functional stay-greens have the
60 protein complexes, thus allowing chl-breakdown
potential to increase plant productivity. In cosmetic stay61 enzymes to access their substrate.
greens, however, retention of chlorophyll during
1
2
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
senescence is uncoupled from a decline of photosynthetic
capacity in these mutants. For many cosmetic stay-green
mutants, including Gregor Mendel’s famous green
cotyledon pea variety, molecular defects were recently
identified in orthologous stay-green genes. Stay-green
genes encode members of a new family of chloroplastlocated proteins, which are likely to function in
dismantling of photosynthetic chlorophyll–apoprotein
complexes. Their activity is considered as a prerequisite
for both chlorophyll and apoprotein degradation during
senescence.
Chlorophyll – friend or foe?
Evolutionary development of advanced life forms on
earth is inseparably linked with the advent of oxygenic
photosynthesis about three billion years ago [1]. This
paved the way for indefinite amounts of water and solar
energy to be used for cellular energy production.
Chlorophyll (chl), the most abundant pigment on earth,
is a key component of photosynthesis required for the
absorption of sunlight. Heterotrophic organisms,
including humans, depend on this source of energy.
Furthermore, the green color of chl also seems to have a
positive psychological effect on humans [2], and green
urban environments have been shown to positively affect
human health [3].
However, chl is a dangerous molecule and a potential
cell phototoxin. This is seen in situations where the
photosynthetic apparatus of plants is overexcited, for
example in high light conditions or after application of
herbicides blocking the photosynthetic electron
transport. Absorbed energy can then be transferred from
chl to oxygen, resulting in the production of reactive
oxygen species (ROS) [4]. Likewise, inhibition of chl
biosynthesis or degradation can lead to the accumulation
of phototoxic intermediates and ROS production [4–6].
The
reactions
from
5-aminolevulinic
acid
to
protoporphyin IX are common to chl and heme
biosynthesis. Thus, related phenotypes occur in humans
suffering from diverse types of porphyria, most of which
are associated with a defect in heme biosynthesis [7].
Many mutants have been identified that are unable to
degrade chl during leaf senescence. Recently, the genetic
defect of some of these mutants was shown to be due to
mutations in a gene called STAY-GREEN (SGR).
Originally, absence of SGR was considered to inhibit chl
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
Chlorophyll-breakdown pathway
Chl biosynthesis comprises at least 15 committed steps,
and genes have been identified for each step in recent
years. Many reviews on the anabolic chl pathway have
been published [8–10]. By contrast, chl catabolism is less
well understood.
For many years, chl degradation during leaf
senescence and fruit ripening was considered a biological
enigma. Only the identification and structure
determination of nonfluorescent chl catabolites (NCCs)
as final breakdown products [11] allowed the stepwise
elucidation of a chl-degradation pathway, as outlined in
Figure 1, which is common in higher plants [12]. Except
NCC-3 of Arabidopsis (Arabidopsis thaliana), all of the
NCCs isolated from plants are derived from chl a [13],
and chl b to chl a conversion has been considered an
early (or probably first) step of degradation [12]. Chl
breakdown continues with the successive removal of
phytol and Mg by chlorophyllase and metal-chelating
substance (MCS) [14], respectively, resulting in
pheophorbide (pheide) a. Pheide a, the last porphyrinic
pigment of breakdown, is subsequently converted via a
red-colored intermediate (red chl catabolite [RCC]) to a
non-colored but blue-fluorescing product termed primary
fluorescent chl catabolite (pFCC). The enzymes
converting chl to pFCC are localized in senescing
chloroplasts, although this issue was a matter of debate
for some time.
Based on sequence information, some of the
molecularly cloned chlorophyllases (termed CLHs) were
proposed to locate extraplastidially [15], which implied
the possible existence of additional chl-breakdown
pathways outside the chloroplast [16]. Recent
investigations [17] indicate that the two CLHs present
in Arabidopsis, even though exhibiting chlorophyllase
activity in vitro [15], are not essential for chl breakdown
during leaf senescence. This questioned their in vivo
relevance, and it was concluded that the genuine
chlorophyllase of Arabidopsis has not been molecularly
cloned yet [17]. By contrast, Citrus CLH was shown to
localize to chloroplasts and to be active in chl breakdown
during fruit ripening [18,19]. Together, these
investigations favor the existence of exclusively plastidlocalized pathways of chl breakdown leading to the
formation of pFCC [12]. pFCC is exported from the
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
plastid by an active transport mechanism [20] before
species-specific modifications occur at several peripheral
side-chain positions in the cytosol [21]. After primary
activated import into the vacuole [22], the modified
FCCs are non-enzymatically converted to their
respective nonfluorescent chl catabolite (NCC) isomers
[23]. Thus, based on the types of modifications to FCC,
different plant species accumulate a characteristic set of
NCCs during senescence [24,25].
Besides the proposed CLH genes, enzymes for three
further catabolic reactions have been molecularly
identified. These are chl b reductase (NON-YELLOW
COLORING1 [NYC1] and NYC-ONE LIKE [NOL])
[26,27], which is involved in chl b to chl a conversion
[28], pheide a oxygenase (PAO) [29], which is responsible
for the oxygenolytic opening of the porphyrin ring of
pheide a to yield RCC, and RCC reductase (RCCR) [30],
which works in concert with PAO to site-specifically
reduce RCC to pFCC. PAO and RCCR defects were
originally identified in the ACCELERATED CELL
DEATH (ACD) mutants acd1 and acd2, respectively
[31,32], and accumulation of the photodynamic
intermediates pheide a and RCC, respectively, has been
shown to be responsible for the observed lesion mimic
phenotypes [6,29].
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
Stay-green mutants
160
161
162
163
164
165
166
167
168
Cosmetic stay-greens as tools for the elucidation of chl
breakdown
Stay-green mutants (Table 1) are known for many plant
species, including different crops, and have been
classified into two principal categories: (i) functional and
(ii) non-functional (also termed cosmetic) mutants [33].
The determining difference is whether retention of green
color (compared to a respective wild-type at a certain
developmental stage) is coupled to (i) retention
(functional stay-greens) or (ii) loss (cosmetic stay-greens)
of photosynthetic activity. Thus, functional stay-green
mutants could be affected in timing of senescence
initiation or speed of senescence progression.
Agronomically, functional stay-green mutants are
interesting because delaying of senescence initiation
(categorized as type A according to the suggested
nomenclature) or progression (type B) might have an
advantageous effect on yield [33]. Thus, for example, the
highest yield per area ever obtained in Zea mays (maize)
was with the stay-green variety FS854 [33], and staygreenness of Oryza sativa (rice) SNU-SG1 is correlated
with increased grain yield [34]. Likewise, delaying
senescence is positively correlated with yield under
water-limiting conditions. The potential of targeting
senescence to increase drought resistance was confirmed
in a recent biotechnological approach, in which droughtinduced production of cytokinin, known to delay
senescence, had a positive effect on plant survival and
yield [35].
In contrast to functional stay-green mutants, cosmetic
mutants (categorized as type C according to the
suggested nomenclature [33]) are likely to be defective in
chl breakdown. Indeed, analysis of type C stay-green
mutants was extremely helpful in the elucidation of the
chl-degradation pathway. Thus, the first identification of
chl-breakdown products was possible because such
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
compounds did not accumulate in the stay-green mutant
of Festuca pratensis, Bf993, compared with a wild-type
variety
[36].
Furthermore,
Bf993
accumulated
chlorophyllide and pheide a, indicating for the first time
that these could be intermediates of breakdown. In the
rice type C mutant, nyc1, chl b was particularly stable,
indicating a lesion in chl b to chl a reduction. This has
recently been confirmed by cloning of NYC1 and a close
homologue, NOL, for which chl b reductase activity could
be demonstrated [26,27]. A similar phenotype has been
described in a cytoplasmically inherited Glycine max
(soybean) mutation, cytG [37], and it can be assumed
that chl b to chl a reduction is also impaired in this
mutant.
For the vast majority of well-known cosmetic staygreen mutants from many different species (some
examples are listed in Table 1), the genetic lesion was
not determined until recently. Likely reasons are the
lack of suitable genetic tools, large genome sizes or
absence of isogenic wild-type varieties in many cases,
which made genetic identification of mutants difficult. A
famous cosmetic stay-green mutant is the green
cotyledon mutant, one of seven Pisum sativum (pea)
varieties used by Gregor Mendel to establish the laws of
genetics. The mutation had been mapped to the I locus
at the end of chromosome 1, but identification of the
gene itself was not successful for many years. Likewise,
mapping analysis of known chl catabolic genes, in
particular PAO and CLH, did not uncover the genetic
defect in Mendel’s pea [38] or the chlorophyll retainer
(cl) mutant of Capsicum annuum (bell pepper) [39]. The
mutation in bell pepper was assumed to be likely to
affect the orthologous gene of the green flesh (gf)
Solanum lycopersicon (tomato) mutant because the
mutations mapped to syntenic regions in both species
[39]. Furthermore, analysis of catabolic enzyme
activities suggested a biochemical defect in PAO in many
of the mutants, such as Mendel’s peas, Bf993 and the
non-yellowing1 (nye1-1) mutant in Arabidopsis. In all
investigated cases, PAO activity was reduced, but not
entirely absent, indicating that the defect could be in a
factor regulating PAO activity [40–43]. In summary, it
seems reasonable to assume that many, but not all, of
the unidentified stay-green mutants would be affected in
orthologous genes.
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
Cloning of the stay-green gene
At least five groups independently succeeded in
identifying the stay-green gene in 2006 and 2007. Two
major strategies were successfully employed: (i) classical
mapping, that is, genetic analysis followed by direct
gene identification through sequencing of the mapped
chromosomal region and verification through mutant
complementation [43–45]; and (ii) a combination of
genetic analysis and usage of publicly available genome
and transcriptome resources [46,47]. The latter strategy
proved particularly successful in identifying the gene in
a
non-model
crop
plant,
Lolium/Festuca.
By
introgression, the stay-green-conferring y locus of Bf993
had been transferred into Lolium species [48,49]. Based
on an extended mapping population segregating for y,
the region could be narrowed down to 10 cM on
chromosome 5 [46], which was within a syntenic region
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
of rice chromosome 9 [50–52] that contained a
quantitative trait locus for stay-green, sgr(t) [53]. From
The Institute for Genomic Research (TIGR) database, 30
gene models were annotated within this region, one of
which (Os09g36200) showed a high degree of similarity
to an Arabidopsis gene (At4g22920) with a senescencerelated expression pattern [54]. Subsequent silencing of
At4g22920 in Arabidopsis confirmed that loss of function
of this gene conferred stay-greenness [47]. Independent
analysis of two rice mutants (both termed sgr) [44,45]
and the Arabidopsis nye1-1 mutant [43] further
identified orthologous genes being responsible for the
stay-green character in respective mutants. Based on
these initial efforts, the genetic lesion of further mutants
could be attributed to defects in the stay-green gene.
These include Mendel’s green cotyledon mutant [47,55],
tomato gf [56], bell pepper cl [56,57] and a further allele
in rice [55]. It can be expected that additional phenotypic
stay-greens, such as soybean d1d2 [58], Phaseolus
vulgaris Alamo [59] and further mutants in bell pepper
[60,61] and Citrus [62] (Table 1), are defective in
orthologous stay-green genes. Different names have
been used in the past [33,43,46,47]. For the future, I
propose the exclusive use of SGR (Box 1).
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
Analysis of the mutations of SGR proteins isolated
from stay-green mutants revealed (i) frameshift or
nonsense [43,46,55] and (ii) in-frame insertion or
missense mutations [44,45,55–57] (Figure 2). All inframe insertion or missense mutations allowed normal
levels of mutant gene expression [44,45,55–57], and
where analyzed, the levels of mutant SGR in stay-green
mutants was comparable to the levels of SGR in wildtype plants [44,45]. Nevertheless, the activity of mutated
proteins was shown to be defective for several different
mutants, as demonstrated by expression in heterologous
plant species. Thus, wild-type pea (PsSGR) and rice
(OsSGR) proteins induced senescence in Nicotiana
benthamiana leaves after transient Agrobacterium
tumefaciens infiltration, whereas the corresponding
mutated forms did not [45,63]. Likewise, the two-aminoacid insertion of the PsSGR allele of Gregor Mendel’s
pea mutant JI2775 was not able to complement the rice
sgr-2 mutant when introduced into OsSGR [55]. In
conclusion, it can be argued that functionality of SGR
proteins depends on the presence of many invariant
amino acid residues, and single-point mutations might
have a dramatic effect on the three-dimensional
structure, which is likely to affect activity.
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
SGR proteins are highly conserved
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
Function of SGR
Sequence comparison of the SGR proteins identified so
far demonstrate a high degree of similarity.
Furthermore, phylogenetic analysis indicates the
existence of three subfamilies of SGR-like proteins in
plants (Figure 2). Clade I (dicot) and clade II (monocots)
contain all SGR proteins, for which absence has been
shown to result in a stay-green phenotype. All members
have a highly conserved C-terminal motif (C-X3-C-X-C2F-P-X5-P), which is separated from the highly
homologous core region of the proteins by a rather
variable region [63]. The function of this motif remains
elusive, although the presence of four cysteine residues
implies possible roles in inter- or intramolecular
crosslinking or in redox regulation. For several species,
such as Arabidopsis, Populus trichocarpa, soybean and
maize, two paralogous SGR proteins have been
identified [45,56,63] (Figure 2), but it is unclear to date
whether both isoforms equally contribute to chl
breakdown. A T-DNA insertion line in AtSGR2 did not
exhibit a stay-green phenotype, and silencing AtSGR1 in
the AtSGR2 mutant background did not enhance the
phenotype compared to silencing AtSGR1 in wild type
[63]. This indicated that AtSGR2 is not involved in
senescence-related chl breakdown. Members of a third
clade of SGR-like proteins, such as At1g44000 of
Arabidopsis, miss this cysteine-rich motif [63], and
experimental analysis is required to elucidate whether
these proteins are also involved in chl breakdown.
Preliminary investigations of an At1g44000-knockout
mutant indicate that it is not affected in senescencerelated chl breakdown (S. Hörtensteiner, unpublished).
SGR proteins showed distant relationship to a group of
bacterial
(Clostridium,
Bacillus)
and
algal
(Chlamydomonas, Ostreococcus) proteins, but no
homologues were found in cyanobacteria [44,56,63].
Again, the role of these SGR-like proteins has not been
elucidated.
Historically, defects in SGR had been correlated with
reduced PAO activity or expression. This was
rationalized by the fact that many stay-green mutants,
for which the genetic lesion has now been attributed to
SGR, exhibited low levels of PAO activity, whereas
activities of other catabolic enzymes, in particular
chlorophyllase and RCCR, were unaffected [40–
43,64,65]. In addition, in several cases increased levels
of chlorophyllide and pheide a have been identified [40–
42,63], indicating a block at the level of PAO. The recent
molecular cloning of PAO [29] and the availability of
PAO antibodies [66] allowed detailed analysis of both
PAO expression and protein abundance in stay-green
mutants. PAO expression was unaltered in rice sgr-2
and Arabidopsis nye1-1 [43,55], and PAO abundance was
identical in several SGR mutants, such as pea JI2775,
Arabidopsis AtSGR1-silencing lines and stay-green
Festuca/Lolium, when compared to respective wild types
[63,67]. Furthermore, differences in PAO activity
correlated with PAO abundance in the extracts used for
assays, indicating that the discrepancy between mutants
and wild type was an artifact that was solely caused by
unequally efficient extraction of PAO [63]. This was
corroborated by inhibitor experiments showing that the
level of pheide a accumulation in JI2775 was
independent of PAO activity. Altogether, these data
unequivocally show that SGR acts independently of
PAO. Because silencing of AtSGR1 in a pao1 background
prevented the pao1-related accumulation of pheide a
[63], it could further be concluded that SGR acts
upstream of PAO.
A common feature of SGR mutants is the retention of
chl-binding proteins of the photosynthetic apparatus
during senescence. In particular, light harvesting
complex II (LHCII) subunits are highly stable in all
SGR-deficient mutants analyzed so far [44,45,55,63,68].
Historically this had been explained by a connection to
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
the simultaneously retained chl, that is, chl degradation,
which was assumed to be defective in SGR mutants, was
considered a prerequisite for the degradation of chlbinding proteins. Bf993 was shown to accumulate a
particular proteolytic fragment of LHCII subunits,
which was devoid of its N-terminal stroma-facing region
[33]. This further pointed to the requirement of chl
degradation for the full degradation of LHC proteins.
However, this view might be wrong. As mentioned
above, PAO and all other catabolic enzymes analyzed so
far are not affected in SGR mutants. The identification
of SGR proteins did not indicate a possible function,
because SGRs do not contain any known domain.
Furthermore, enzymatic activities of chl catabolic steps,
such as chlorophyllase [45] or Mg-dechelation (S. Aubry
and S. Hörtensteiner, unpublished) could not be
attributed to SGRs. Extraction of chl from chl–protein
complexes and binding to a carrier protein was
considered a requirement for proper chl and (possibly)
apoprotein degradation [69]. Yet, in contrast to a known
chl-binding protein, water soluble chl-binding protein
[70,71], SGR was not able to bind chl in vitro [45]. Thus,
it is reasonable to assume that SGR is not an enzyme at
all. Recent co-immunoprecipitation experiments [45]
demonstrated that OsSGR was able to specifically bind
LHCII subunits in vivo but did not interact with LHCI
subunits or chl-binding core complex subunits, such as
D1. Interestingly, this binding also occurred in the
V99M mutation of OsSGR, indicating that the mutation
did not affect binding. It was suggested that the
mutation might affect an (unknown) enzymatic activity
or might disrupt binding of further regulatory factors
[45]. Functional analysis of other SGR point mutations
is required to confirm this suggestion.
In conclusion, SGRs are likely candidates for protein
factors involved in LHCII disassembly, and absence of
SGR during senescence only indirectly causes retention
of chl within the stable apoproteins. In this respect, SGR
expression would be a prerequisite for chl breakdown
(Figure 3) but not a catabolic factor itself. Interestingly,
also in NYC1 and NOL mutants, chl and chl-binding
proteins are retained [26,27]. Thus, it seems possible
that both factors are equally and simultaneously
important to induce destabilization of the chl–protein
complexes to induce chl breakdown (Figure 3).
Furthermore, reduced mRNA levels of AtSGR1 during
senescence in PAO mutants [45] demonstrated that a
feedback mechanism exists, probably through the
accumulation of pheide a, which prevents further
apoprotein disassembly and thus further chl breakdown.
Such a regulatory mechanism could be seen as a security
control to make sure that chl degradation only occurs or
proceeds when the chl catabolic machinery is fully
active. Thus, besides the regulation of catabolic enzyme
activity or expression [18,19,26,27,72,73], the regulation
of apoprotein disassembly through SGR (and/or
NYC1/NOL) can be considered a master switch required
to initiate chl breakdown.
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
Conclusions and future perspectives
482
Chl-binding proteins within the two photosystems 483
contain a significant proportion of total cellular nitrogen 484
485
(around 20%), which plants are attuned to efficiently 486
recycle during leaf senescence [12]. The tight linkage of
apoprotein and chl degradation as seen in many staygreen mutants is rationalized by the fact that unbound
chl is phototoxic. In this sense, the proposed role of SGR
as a destabilizing factor of chl–protein complexes
provides an elegant control point of degradation. This is
supported by the finding that constitutive increase of
SGR levels causes premature chl degradation [43,45],
whereas no similar effect is obtained when
overexpressing PAO [74]. Absence of SGR mainly affects
degradation of LHCII subunits, and it would be of
interest to analyze in detail the structure composition of
photosynthetic complexes during senescence in SGR
mutants. The mechanism of SGR function remains
unknown. It is possible that SGR binding to LHC
recruits further proteins required for complexdisintegration. In such a scenario, the formation at the
site of degradation of a multienzyme complex containing
proteases and/or chl-catabolic enzymes seems likely.
Alternatively, SGR exhibits an as yet unidentified
activity that significantly changes the chl–apoprotein
complex structure and subsequently enables catabolic
enzymes to degrade the complex constituents. However,
the factors involved in proteolysis of chl-binding proteins
are unknown. Thus, to date, the possible function of SGR
can only be tested experimentally in relation to chl
breakdown.
References
1
Xiong, J. and Bauer, C.E. (2002) Complex evolution of
photosynthesis. Annu. Rev. Plant Biol. 53, 503–521
2
Pretty, J. et al. (2007) Green exercise in the UK
countryside: effects on health and physiological well-being, and
implications for policy and planning. J. Environ. Plann.
Manage. 50, 211–231
3
Tsoulas, K. et al. (2007) Promoting ecosystem and human
health in urban areas using Green Infrastructure: a literature
review. Landsc. Urban Plan. 81, 167–178
4
Apel, K. and Hirt, H. (2004) Reactive oxygen species:
metabolism, oxidative stress, and signal transduction. Annu.
Rev. Plant Biol. 55, 373–399
5
Hu, G. et al. (1998) A porphyrin pathway impairment is
responsible for the phenotype of a dominant disease lesion
mimic mutant of maize. Plant Cell 10, 1095–1105
6
Pružinská, A. et al. (2007) In vivo participation of red
chlorophyll catabolite reductase in chlorophyll breakdown. Plant
Cell 19, 369–387
7
Anderson, K.E. et al. (2005) Recommendations for the
diagnosis and treatment of the acute porphyrias. Ann. Intern.
Med. 142, 439–450
8
Beale, S.I. (2005) Green genes gleaned. Trends Plant Sci.
10, 309–312
9
Eckhardt, U. et al. (2004) Recent advances in chlorophyll
biosynthesis and breakdown in higher plants. Plant Mol. Biol.
56, 1–14
10 Bollivar, D.W. (2006) Recent advances in chlorophyll
biosynthesis. Photosynth. Res. 90, 173–194
11 Kräutler, B. et al. (1991) On the enigma of chlorophyll
degradation: the constitution of a secoporphinoid catabolite.
Angew. Chem. Int. Ed. Engl. 30, 1315–1318
12 Hörtensteiner, S. (2006) Chlorophyll degradation during
senescence. Annu. Rev. Plant Biol. 57, 55–77
13 Müller, T. et al. (2006) A divergent path of chlorophyll
breakdown in the model plant Arabidopsis thaliana.
ChemBioChem 7, 40–42
14 Suzuki, T. et al. (2005) Mg-dechelation activity in radish
cotyledons with artificial and native substrates, Mgchlorophyllin a and chlorophyllide a. Plant Physiol. Biochem. 43,
459–464
15 Tsuchiya, T. et al. (1999) Cloning of chlorophyllase, the key
enzyme in chlorophyll degradation: finding of a lipase motif and
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
the induction by methyl jasmonate. Proc. Natl. Acad. Sci. U. S.
A. 96, 15362–15367
16 Takamiya, K.I. et al. (2000) Degradation pathway(s) of
chlorophyll: what has gene cloning revealed? Trends Plant Sci.
5, 426–431
17 Schenk, N. et al. (2007) The chlorophyllases AtCLH1 and
AtCLH2 are not essential for senescence-related chlorophyll
breakdown in Arabidopsis thaliana. FEBS Lett. 581, 5517–5525
18 Harpaz-Saad, S. et al. (2007) Chlorophyllase is a ratelimiting
enzyme
in
chlorophyll
catabolism and
is
posttranslationally regulated. Plant Cell 19, 1007–1022
19 Azoulay Shemer, T. et al. (2008) Citrus chlorophyllase
dynamics at ethylene-induced fruit color-break; a study of
chlorophyllase expression, post-translational processing kinetics
and in-situ intracellular localization. Plant Physiol. 148, 108–
118
20 Matile, P. et al. (1992) Production and release of a
chlorophyll catabolite in isolated senescent chloroplasts. Planta
187, 230–235
21 Kräutler, B. (2003) Chlorophyll breakdown and chlorophyll
catabolites. In The Porphyrin Handbook (Vol. 13) (Kadish, K.M.
et al., eds), pp. 183–209, Elsevier Science
22 Hinder, B. et al. (1996) How plants dispose of chlorophyll
catabolites. Directly energized uptake of tetrapyrrolic
breakdown products into isolated vacuoles. J. Biol. Chem. 271,
27233–27236
23 Oberhuber, M. et al. (2003) Breakdown of chlorophyll: a
nonenzymatic reaction accounts for the formation of the
colorless ‘nonfluorescent‘ chlorophyll catabolites. Proc. Natl.
Acad. Sci. U. S. A. 100, 6910–6915
24 Kräutler, B. and Hörtensteiner, S. (2006) Chlorophyll
catabolites and the biochemistry of chlorophyll breakdown. In
Chlorophylls
and
Bacteriochlorophylls:
Biochemistry,
Biophysics, Functions and Applications (Vol. 25) (Grimm, B. et
al., eds), pp. 237–260, Springer
25 Müller, T. et al. (2007) Colorless tetrapyrrolic chlorophyll
catabolites found in ripening fruit are effective antioxidants.
Angew. Chem. Int. Ed. 46, 8699–8702
26 Kusaba, M. et al. (2007) Rice NON-YELLOW COLORING1
is involved in light-harvesting complex II and grana degradation
during leaf senescence. Plant Cell 19, 1362–1375
27 Sato,
Y.
et
al.
(2009)
Two
short-chain
dehydrogenase/reductases, NON-YELLOW COLORING 1 and
NYC1-LIKE, are required for chlorophyll b and light-harvesting
complex II degradation during senescence in rice. Plant J. 57,
120–131
28 Rüdiger, W. (2002) Biosynthesis of chlorophyll b and the
chlorophyll cycle. Photosynth. Res. 74, 187–193
29 Pružinská, A. et al. (2003) Chlorophyll breakdown:
pheophorbide a oxygenase is a Rieske-type iron-sulfur protein,
encoded by the accelerated cell death 1 gene. Proc. Natl. Acad.
Sci. U. S. A. 100, 15259–15264
30 Wüthrich, K.L. et al. (2000) Molecular cloning, functional
expression and characterisation of RCC reductase involved in
chlorophyll catabolism. Plant J. 21, 189–198
31 Greenberg, J.T. and Ausubel, F.M. (1993) Arabidopsis
mutants compromised for the control of cellular damage during
pathogenesis and aging. Plant J. 4, 327–341
32 Greenberg, J.T. et al. (1994) Programmed cell death in
plants: a pathogen-triggered response activated coordinately
with multiple defense functions. Cell 77, 551–563
33 Thomas, H. and Howarth, C.J. (2000) Five ways to stay
green. J. Exp. Bot. 51, 329–337
34 Yoo, S.C. et al. (2007) Quantitative trait loci associated
with functional stay-green SNU-SG1 in rice. Mol. Cells 24, 83–
94
35 Rivero, R.M. et al. (2007) Delayed leaf senescence induces
extreme drought tolerance in a flowering plant. Proc. Natl.
Acad. Sci. U. S. A. 104, 19631–19636
36 Thomas, H. et al. (1989) Catabolism of chlorophyll in vivo:
significance of polar chlorophyll catabolites in a non-yellowing
senescence mutant of Festuca pratensis Huds. New Phytol. 111,
3–8
37 Canfield, M.R. et al. (1995) Alteration of soybean seedling
development in darkness and light by the stay-green mutation
cytG and Gd1d2. Ann. Bot. (Lond.) 75, 143–150
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
38 Moffet, M.D. and Weeden, N.F. (2005) Pheophorbide a
monooxygenase (Pao) is located on LG VII near Amy in pea and
lentil. Pisum Genet. 37, 24–29
39 Efrati, A. et al. (2005) Molecular mapping of the
chlorophyll retainer (cl) mutation in pepper (Capsicum spp.) and
screening for candidate genes using tomato ESTs homologous to
structural genes of the chlorophyll catabolism pathway. Genome
48, 347–351
40 Vicentini, F. et al. (1995) Chlorophyll breakdown in
senescent leaves: identification of the biochemical lesion in a
stay-green genotype of Festuca pratensis Huds. New Phytol. 129,
247–252
41 Thomas, H. et al. (1996) Gregor Mendel’s green and yellow
pea seeds. Bot. Acta 109, 3–4
42 Roca, M. et al. (2004) Analysis of the chlorophyll
catabolism pathway in leaves of an introgression senescence
mutant of Lolium temulentum. Phytochemistry 65, 1231–1238
43 Ren, G. et al. (2007) Identification of a novel chloroplast
protein AtNYE1 regulating chlorophyll degradation during leaf
senescence in Arabidopsis. Plant Physiol. 144, 1429–1441
44 Jiang, H. et al. (2007) Molecular cloning and function
analysis of the stay green gene in rice. Plant J. 52, 197–209
45 Park, S-Y. et al. (2007) The senescence-induced staygreen
protein regulates chlorophyll degradation. Plant Cell 19, 1649–
1664
46 Armstead, I. et al. (2006) From crop to model to crop:
identifying the genetic basis of the staygreen mutation in the
Lolium/Festuca forage and amenity grasses. New Phytol. 172,
592–597
47 Armstead, I. et al. (2007) Cross-species identification of
Mendel’s I locus. Science 315, 73
48 Thomas, H. et al. (1997) Introgression, tagging and
expression of a leaf senescence gene in Festulolium. New Phytol.
137, 29–34
49 Moore, B.J. et al. (2005) Molecular tagging of a senescence
gene by introgression mapping of a stay-green mutation from
Festuca pratensis. New Phytol. 165, 801–806
50 Armstead, I.P. et al. (2002) Comparison and integration of
genetic maps generated from F2 and BC1-type mapping
populations in perennial ryegrass. Plant Breed. 121, 501–507
51 Alm, V. et al. (2003) A linkage map of meadow fescue
(Festuca pratensis Huds) and comparative mapping with other
Poaceae species. Theor. Appl. Genet. 108, 5–40
52 Sim, S. et al. (2005) Chromosomal rearrangements
differentiating the ryegrass genome from the Triticeae, oat, and
rice genomes using common heterologous RFLP probes. Theor.
Appl. Genet. 110, 1011–1019
53 Cha, K.W. et al. (2002) Isolation, characterization, and
mapping of the stay green mutant in rice. Theor. Appl. Genet.
104, 526–532
54 Zimmermann, P. et al. (2004) GENEVESTIGATOR.
Arabidopsis microarray database and analysis toolbox. Plant
Physiol. 136, 2621–2632
55 Sato, Y. et al. (2007) Mendel’s green cotyledon gene
encodes a positive regulator of the chlorophyll-degrading
pathway. Proc. Natl. Acad. Sci. U. S. A. 104, 14169–14174
56 Barry, C.S. et al. (2008) Amino acid substitutions in
homologs of the STAY-GREEN protein are responsible for the
green-flesh and chlorophyll retainer mutations of tomato and
pepper. Plant Physiol. 147, 179–187
57 Borovsky, Y. and Paran, I. (2008) Chlorophyll breakdown
during pepper fruit ripening in the chlorophyll retainer
mutation is impaired at the homolog of the senescence-inducible
stay-green gene. Theor. Appl. Genet. 117, 235–240
58 Luquez, V.M. and Guiamet, J.J. (2002) The stay green
mutations d1 and d2 increase water stress susceptibility in
soybeans. J. Exp. Bot. 53, 1421–1428
59 Bachmann, A. et al. (1994) Stay-green genotypes of
Phaseolus vulgaris L.: chloroplast proteins and chlorophyll
catabolites during foliar senescence. New Phytol. 126, 593–600
60 Roca, M. et al. (2006) Stay-green phenotype slows the
carotenogenic process in Capsicum annuum (L.) fruits. J. Agric.
Food Chem. 54, 8782–8787
61 Roca, M. and Minguez-Mosquera, M.I. (2006) Chlorophyll
catabolism pathway in fruits of Capsicum annuum (L.): staygreen versus red fruits. J. Agric. Food Chem. 54, 4035–4040
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
62 Alós, E. et al. (2008) An evaluation of the basis and
consequences of a stay-green mutation in the navel negra Citrus
mutant using transcriptomic and proteomic profiling and
metabolite analysis. Plant Physiol. 147, 1300–1315
63 Aubry, S. et al. (2008) Stay-green protein, defective in
Mendel’s green cotyledon mutant, acts independent and
upstream of pheophorbide a oxygenase in the chlorophyll
catabolic pathway. Plant Mol. Biol. 67, 243–256
64 Moser, D. and Matile, P. (1997) Chlorophyll breakdown in
ripening fruits of Capsicum annuum. J. Plant Physiol. 150, 759–
761
65 Akhtar, M.S. et al. (1999) Altered patterns of senescence
and ripening in gf, a stay-green mutant of tomato (Lycopersicon
esculentum Mill.). J. Exp. Bot. 50, 1115–1122
66 Gray, J. et al. (2004) A small family of LLS1-related nonheme oxygenases in plants with an origin amongst oxygenic
photosynthesizers. Plant Mol. Biol. 54, 39–54
67 Ougham, H. et al. (2008) The control of chlorophyll
catabolism and the status of yellowing as a biomarker of leaf
senescence. Plant Biol. 10 (Suppl. 1), 4–14
68 Hilditch, P.I. et al. (1989) Leaf senescence in a nonyellowing mutant of Festuca pratensis: proteins of photosystem
II. Planta 177, 265–272
69 Matile, P. et al. (1999) Chlorophyll degradation. Annu. Rev.
Plant Physiol. Plant Mol. Biol. 50, 67–95
70 Satoh, H. et al. (1998) Molecular cloning and functional
expression of a water-soluble chlorophyll protein, a putative
carrier of chlorophyll molecules in cauliflower. J. Biol. Chem.
273, 30568–30575
71 Satoh, H. et al. (2001) Water-soluble chlorophyll protein in
Brassicaceae plants is a stress-induced chlorophyll-binding
protein. Plant Cell Physiol. 42, 906–911
O
N
H
N
N
NYC1/NOL
Mg
N
O
N
O
Chlorophyllase
O
Chl b
O
O
O
NH
RCCR
OH
O
OH
OMe
Pheide a
O
R1
O
H
NH
HN
N
OMe
O
OH
NH
HN
O
O
RCC
O
HN
R2
H
HN
O
HN
O
OMe
O
PAO
O
O
O
H
HN
N
N
N
Chlorophyllide a
O
H
701
702
703
704
705
OH
N
MCS
O
OPhytol OMe
Chl a
NH
NH
N
Mg
N
N
O
OPhytol OMe
N
N
Mg
N
O
72 Pružinská, A. et al. (2005) Chlorophyll breakdown in
senescent Arabidopsis leaves: characterization of chlorophyll
catabolites and of chlorophyll catabolic enzymes involved in the
degreening reaction. Plant Physiol. 139, 52–63
73 Chung, D.W. et al. (2006) The role of pheophorbide a
oxygenase expression and activity in the canola green seed
problem. Plant Physiol. 142, 88–97
74 Yang, M. et al. (2004) The wound-inducible Lls1 gene from
maize is an orthologue of the Arabidopsis Acd1 gene, and the
LLS1 protein is present in non-photosynthetic tissues. Plant
Mol. Biol. 54, 175–191
75 Oh, M.H. et al. (2003) Increased stability of LHCII by
aggregate formation during dark-induced leaf senescence in the
Arabidopsis mutant, ore10. Plant Cell Physiol. 44, 1368–1377
76 Lim, P.O. et al. (2006) Leaf senescence. Annu. Rev. Plant
Biol. 58, 115–136
77 Yoshida, S. et al. (2002) A delayed leaf senescence mutant
is defective in arginyl-tRNA: protein arginyltransferase, a
component of the N-end rule pathway in Arabidopsis. Plant J.
32, 129–137
78 Gong, Y.H. et al. (2005) Slow export of photoassimilate
from stay-green leaves during late grain-filling stage in hybrid
winter wheat (Triticum aestivum L.). J. Agron. Crop Sci. 191,
292–299
79 Spano, G. et al. (2003) Physiological characterization of
‘stay green’ mutants in durum wheat. J. Exp. Bot. 54, 1415–
1420
80 Dereeper, A. et al. (2008) Phylogeny.fr: robust phylogenetic
analysis for the non-specialist. Nucleic Acids Res. 36, W465–
W469
O
O
OMe
pFCC
HN
O
OH
O
OR3
NCCs
TRENDS in Plant Science
Figure 1. Pathway of chlorophyll breakdown in higher plants. The chemical structures of chl and of chl catabolites are shown. R1–R3 indicates the presence of species-specific
modifications in NCCs from different plants [12]. Abbreviations: chl, chlorophyll; FCC, fluorescent chl catabolite; MCS, metal-chelating substance; NCC, nonfluorescent chl
catabolite; NYC1/NOL, NON YELLOW COLORING1/NYC-ONE LIKE (evidence shows that both NYC1 and NOL interact to give a functional enzyme [27]); PAO, pheide a
oxygenase; pFCC, primary FCC; pheide, pheophorbide; RCC, red chl catabolite; RCCR, RCC reductase.
(a)
CaSGR
90
SlSGR
74
85
NtSGR
AtSGR1
87
AtSGR2
87
I
100
83
GmSGR2
93
GmSGR1
PsSGR
PtSGR2
95
PtSGR1
SbSGR
77
ZmSGR1
87
ZmSGR2
II
100
OsSGR
HvSGR
OsSGR3
III
100
OsSGR2
100
AtSGR3
0.1
nye1-1: L10>Stop
(b)
PsSGR
AtSGR1
SlSGR
CaSGR
OsSGR
:
:
:
:
:
JI2775: N38>K
JI2775: T12>S
M--DTLTSAPLLTTKFKPSFSPQQKPC------FPHRRRFENGKKNQS------IVPVARLFGPAIFEASKLKVL
M--CSLSAIMLLPTKLKPAYSDKRSNSSSSSSLFFNN-RRSK-KKNQS------IVPVARLFGPAIFESSKLKVL
M--GTLTTSLVVPSKLNNE---------QQSSIFIHKTRRKC-KKNQS------IVPVARLFGPAIFEASKLKVL
M--GTLTASLVAPSKLNPE---------KHSSLFVYKTRRKS-HKNQS------IVPVARLFGPAIFEASKLKVL
MAAATSTMSLIPPITQQQR---------WHAADSLVVLASRR-HDSRRRRRCRYVVPRARLFGPAIFEASKLKVL
:
:
:
:
:
61
65
57
57
65
:
:
:
:
:
134
138
130
130
140
:
:
:
:
:
209
213
205
205
215
sgr-2: 8 bp deletion
PsSGR
AtSGR1
SlSGR
CaSGR
OsSGR
:
:
:
:
:
FLGIDENKH--PGNLPRTYTLTHSDVTSKLTLAISQTINNSQLQGWYNRLQRDEVVAQWKKVKGKMSLHVHCHIS
FLGVDEKKH--PSTLPRTYTLTHSDITAKLTLAISQSINNSQLQGWANRLYRDEVVAEWKKVKGKMSLHVHCHIS
FLGVDEEKH--PGKLPRTYTLTHSDITSKLTLAISQTINNSQLQGWYNRLQRDEVVAEWKKVKGKMSLHVHCHIS
FLGVDEKKH--PGKLPRTYTLTHSDITSKLTLAISQTINNSQLQGWYNRLQRDEVVAEWKKVKGKMSLHVHCHIS
FLGVDEEKHQHPGKLPRTYTLTHSDVTARLTLAVSHTINRAQLQGWYNKLQRDEVVAEWKKVQGHMSLHVHCHIS
sgr-3:Y84>C
PsSGR
AtSGR1
SlSGR
CaSGR
OsSGR
:
:
:
:
:
sgr-1:V99>M
y:4 bp insertion
cl: W114>R
JI2775: 6 bp insertion
GGHFLLDIFARLRYFIFCKELPVVLKAFVHGDGNLFNNYPELEESLVWVFFHSKIREFNKVECWGPLKEASQPTS
GGHFLLDLFAKFRYFIFCKELPVVLKAFVHGDGNLLNNYPELQEALVWVYFHSNVNEFNKVECWGPLWEAVSPDG
GGHFMLDLFARLRNYIFCKELPVVLKAFVHGDENLLRNYPELQEALVWVYFHSNIQEFNKVECWGPLRDATSPSS
GGHFMLDLFARLRYYIFCKELPVVLKAFVHGDENLLKNYPELQQALVWVYFHSNIQEFNKVECWGPLKDAASPSS
GGHVLLDLIAGLRYYIFRKELPVVLKAFVHGDGNLFSRHPELEEATVWVYFHSNLPRFNRVECWGPLRDAGAPPE
gf: R143>S
PsSGR
AtSGR1
SlSGR
CaSGR
OsSGR
:
:
:
:
:
GTHSDL----------------KLPQSCEEDCECCFPPLNLSPIPCSNEV-----INNTYEPIDGIGTQHGNLHKTETLPEA-----------------RCADECSCCFPTVSSIPWSHSLSNEGVNGYSGTQT--EGIATPNPEKL
SSGGVGGVKSTSFTSNSNKKW-ELPKPCEEACACCFPPVSVMPWLSS-NLDGVGEENGTIQ--QGLQEQQS--S--GVGGGMNTSFTSNSNIKW-NLPKPCEETCTCCFPPMSVIPWPSTTNV-----ENGTIQ--QGLQEQQS--EDDAVAAAAAEEVAAEQMPAAGEWPRRCPGQCDCCFPPYSLIPWPHQHDVAAADGQ-----PQQ----------
:
:
:
:
:
261
268
272
266
274
Cysteine-rich motif
706
707
708
709
710
711
712
713
714
715
TRENDS in Plant Science
Figure 2. Phylogenetic analysis and sequence alignment of SGR proteins from higher plants. (a) Maximum likelihood phylogenetic tree of SGR proteins. Sequences were
aligned and the tree constructed at phylogeny.fr (see http://www.phylogeny.fr) [80]. Branch support values from 100 bootstraps are indicated when higher than 50%. Three
clades (I–III) are distinguished. GenBank protein accession numbers are as follows: Arabidopsis thaliana AtSGR1, AAW82962; AtSGR2, AAU05981; AtSGR3, AAM14392;
Capsicum annuum CaSGR, ACB56586; Glycine max GmSGR1, AAW82959; GmSGR2, AAW82960; Hordeum vulgare HvSGR, AAW82955; Nicotiana tabacum NtSGR,
ABY19382; Oryza sativa OsSGR1, AAW82954; OsSGR2, BAF16284; OsSGR3, CAE05787; Pisum sativum PsSGR, CAP04954; Solanum lycopersicon SlSGR, ACB56587;
Sorghum bicolor SbSGR, AAW82958; Zea mays ZmSGR1, AAW82956; ZmSGR2, AAW82957. Populus trichocarpa protein sequences were obtained from the Joint Genome
Institute (see http://jgi.doe.gov), and the protein IDs are as follows: PtSGR1, 548540; PtSGR2, 646534. (b) Sequence alignment of SGR proteins. Black shading with white
letters, gray shading with white letters and gray shading with black letters indicate 80%, 60% and 40% sequence identity, respectively. Sites of mutations are highlighted in red. In
each case, the type or consequence of mutation found in different SGR mutants is indicated. A conserved cysteine-rich motif is underlined.
Chl b
Chl a
LHC
Senescence induction
SGR
Chl b
NYC1
Chl a
LHC
Proteases
SGR
Chl b
NYC1
Chl a
Proteases
LHC
Proteases
716
717
718
719
720
721
722
723
724
725
Breakdown
pathway
TRENDS in Plant Science
Figure 3. Model for chlorophyll (chl)–apoprotein complex degradation during senescence. The model schematically depicts light harvesting complex (LHC; solid line) containing
both chl a and chl b. Upon senescence induction, SGR and NYC1 (chl b reductase) are expressed, which cause structural changes of the complex (indicated by a broken line).
These initial changes allow the subsequent breakdown of chl (green color is lost), as well as degradation of LHC proteins by as-yet-unknown proteases.
Box 1. Suggestion of a unified nomenclature for stay-green genes
For historical reasons, different names have been used for mutations in the same stay-green gene. To uniform the use and to allow better gene
recognition, I propose to exclusively use the term stay-green and to abbreviate with SGR. To distinguish between different species, a two-letter code
should be used and an index should be added in cases where more than one SGR gene is present in an organism. Thus, in Arabidopsis, the two SGR
genes would be termed AtSGR1 (At4g22920) and AtSGR2 (At4g11910).
Table 1. Stay-green mutants and varieties identified in different plant speciesa
Species
Mutant or variety
Type of stay-greenb
Function
Refs
Arabidopsis thaliana
nye1-1
ore10
ore11
ore1
ore4-1
ore7
ore9
ore12
dls1
cl
Negral
nan
Bf993
y
cytG
d1d2
nyc1
sgr
SNU-SG1
Alamo
JI2775
gf
QL41
XN901
139; 142; 196; 504
FS854
Cosmetic
Cosmetic
Cosmetic
Functional
Functional
Functional
Functional
Functional
Functional
Cosmetic
Cosmetic
Cosmetic
Cosmetic
Cosmetic
Cosmetic
Cosmetic
Cosmetic
Cosmetic
Functional
Cosmetic
Cosmetic
Cosmetic
Cosmetic
Functional
Functional
Functional
SGR
ND
ND
NAC transcription factor
Plastid ribosomal protein17
AT-hook transcription factor
F-box protein
Arabidopsis histidine kinase3
Arginyl tRNA:protein transferase
SGR
ND
ND
SGR
SGR
ND
ND
Chlorophyll b reductase
SGR
ND
ND
SGR
SGR
ND
ND
ND
ND
[43]
[75]
[75]
[76]
[76]
[76]
[76]
[76]
[77]
[56,57]
[60,61]
[62]
[40]
[46,47]
[37]
[37]
[26]
[44,45,55]
[34]
[59]
[47,55,63]
[56]
[33]
[78]
[79]
[33]
Capsicum annuum
Citrus sinensis
Festuca pratensis
Festuca/Lolium introgressions
Glycine max
Oryza sativa
Phaseolus vulgaris
Pisum sativum
Solanum lycopersicon
Sorghum bicolor
Triticum aestivum
Triticum durum
Zea mays
a
Mutants or varieties were identified in natural populations, mutagenesis screens or in breeding programs.
b
Stay-green categories according to Howard Thomas and Catherine J. Howarth [33].
726
Abbreviations: NAC, NAM (NO APICAL MERISTEM), ATAF1,2, CUC2 (CUP-SHAPED COTYLEDON 2); ND, not determined.