PULS/CE 17
Public Understanding of Life Sciences / Chemical Ecology
Newsletter April 2011
Host Change Alters Toxic Cocktail
Due to a gene modification leaf beetle larvae attacking birch trees produce
toxic cocktails that differ from the ones produced by conspecifics living on
willows … p. 3
Small Genetic Changes with Major Consequences
Small changes have big consequences, some of which may lead to the
development of new weapons in the evolutionary arms race between
plants and herbivores … p. 4
Antibiotics in situ
Scientists are looking for antibiotics produced by microbial symbionts of
leaf-cutting ants and study their function in the ecosystem … p. 5
PULS/CE 17
2
Newsletter April 2011 | Editorial
PULS/CE 17 reports on two particular stories involving small molecular differences which have
important consequences. A leaf beetle species
has been shown capable of turning to birch trees
instead of willows as hosts because of a minor
“malfunction” in processing genetic information.
Amino acid sequence comparison of salicyl alcohol oxidases in different leaf beetles: a vacancy is
visible in the amino acid sequence of Chrysomela lapponica beetles feeding on birch (red area) .
More information on this topic is available on page 3.
Picture: PNAS
Little Differences
Dear Readers!
“The little difference and its huge consequences”
was the title of one of the most successful books
to come out of the young Bonn republic. Alice
Schwarzer‘s ground-breaking work was published
in 1975, when West Germany was democratically
maturing and – despite its 26 years of peaceful
existence – still somehow unsettled.
Although Schwarzer had something completely
different in mind than the topics in this month‘s
newsletter – she was fighting for equal rights
between men and women – “little differences
can have major consequences“ is true in many
contexts.
A second example demonstrates that today’s
Brassicaceae species can defend themselves
successfully against herbivory by producing certain glucosinolates after an amino-acid-producing enzyme switches from producing leucine to
synthesizing glucosinolates (their strong taste
and smell is typical of cabbage) just because its
polypeptide chain is shortened.
Although Alice Schwarzer and molecular biology
seem to have nothing in common, you should be
reminded that males and females have only one
tiny genetic difference – tiny as far as the basic
course of development for a human ovum after
fertilization is concerned: Only the composition of
the 23rd chromosome pair in Homo sapiens determines the developing embryo’s sex. This little XX
versus XY difference has had huge consequences, sociological and biological. We are a long way
from understanding all of them.
Enjoy a beautiful spring and our new PULS/CE
issue!
Jan-W. Kellmann
PULS/CE 17
Research Highlight | Newsletter April 2011
Host Change
Alters Toxic
Cocktail
Leaf beetles fascinate us because of their amazing variety of shapes and rich coloring. Their
larvae, however, are dangerous plant pests.
Beetle larvae are part of a food chain; they are
attacked by predatory insects and parasites. To
protect themselves, they emit substances from
their defensive glands. These defensive secretions contain toxins, such as butyric acid esters or
salicylaldehyde, which the larvae sequester from
chemical precursors they have ingested with their
food. Most leaf beetle species use only one plant
species for feeding and reproducing on. Larvae of
the leaf beetle Chrysomela lapponica attack two
different tree species: willow and birch. On the
one hand, the uptake of special plant molecules
as substrates for toxin-producing enzymes is economical for the beetle larvae; on the other hand,
the leaf beetles become strongly dependent on
the host plant and its specific metabolites. Willows of the Salicaceae family have up to 5 percent glycosylated salicyl alcohol (salicin) in their
leaves, whereas birch trees contain none of these
compounds. Hence, researchers have investigated how Chrysomela lapponica leaf beetles adapted to both birch and willow as host trees and
analyzed whether the loss of salicylaldehyde in
birch feeders is due only to the fact that the precursor salicin is not available in birch. To test their
hypothesis, they offered willow leaves to hungry
leaf beetle larvae they had collected from birch
trees. “The beetles were able to ingest salicin
from willow leaves; salicyl alcohol was also detected in their defensive secretions. However, the
alcohol was not transformed to an aldehyde; this
means that birch feeders lack the enzyme salicyl
alcohol oxidase (SAO), which is responsible for
the oxidation from alcohol to aldehyde,” explains
Roy Kirsch, PhD student in the Department of Bioorganic Chemistry and author of the study.
Biochemical analyses revealed that the gland
secretions of salicylaldehyde-producing willow
beetles contain this enzyme in strikingly large
amounts. The scientists labeled it SAO-W (W:
willow). Using corresponding DNA sequence
data, they isolated and characterized the SAOB (B: birch) encoding gene from birch feeders.
They found that the amino acid sequences of
both enzymes are 97 percent identical. However,
SAO-B is inactive because 27 amino acids at the
beginning of the polypeptide chain are missing.
Further studies on the defensive glands of birch
feeders have shown that the amount of messenger RNA (mRNA) in the SAO-B gene was reduced
by 1000-fold compared to that in willow beetles;
the protein and its enzyme activity were below
the detection level. The lack of enzyme activity is
caused by a mutation in the SAO-B gene located
near the second exon/intron junction. The mutation is responsible for changes in mRNA processing, so-called alternative splicing, which leads to
the loss of 27 amino acids in the SAO-B enzyme.
The scientists conclude that Chrysomela lapponica likely used willows exclusively as host plants
and later shifted to birch trees as well. “It is still
unclear whether the gene mutation enabled the
host plant shift from willow to birch or whether it
was adapted in the course of evolution after the
shift to birch had occurred,” says Wilhelm Boland
By not producing the costly enzyme, birch beetles
can save resources .First and foremost the loss
of salicylaldehyde also means that birch-feeding
populations no longer betray themselves to their
own enemies anymore, who can trace them because of the odorous substance. [JWK, AO]
A leaf beetle larva (Chrysomela
lapponica) emits toxic secretions,
visible as vesicles, from its defensive
glands as a chemical protection against
predators. Photo: Kerstin Ploss, MPI-CE
Roy Kirsch
Photo: MPI-CE
Original Publication:
Kirsch, R., Vogel, H., Muck, A.,
Reichwald, K., Pasteels, J. M., Boland,
W. (2011). Host plant shifts affect a
major defense enzyme in Chrysomela
lapponica. Proceedings of the
National Academy of Sciences USA,
108, 4897-4901.
PULS/CE 17
Newsletter April 2011 | Research Highlight
Small Genetic Changes with
Major Consequences
Plants of the mustard family, such as
Plants are continually exposed to herbivore attack. To defend themselves, they have developed
sophisticated chemical defense mechanisms.
Plants of the mustard family, such as thale cress
(Arabidopsis thaliana), produce glucosinolates
(mustard oil glucosides) to protect themselves
against herbivory. If insect larvae feed on mustard plants, glucosinolates are hydrolyzed to
form toxic isothiocyanates. Chemists call this the
“mustard oil bomb.”
cabbage, produce glucosinolates that
help to fend off herbivorous insects.
The enzyme MAM is responsible
for glucosinolate production. In the
course of evolution the enzyme IPMS
(three dimensional model), which is
involved in the formation leucine, was
converted to MAM: 120 amino acids
disappeared (represented as pale-colored) and two mutations in the active
site of the molecule occurred. Since
then, MAM’s role has been to synthesize precursors of glucosinolates.
Photo: Angela Schneider, MPI-CE;
enzyme model based on Koon, PNAS
101, 2004.
Original Publication:
De Kraker, J.-W., Gershenzon, J.
(2011). From Amino Acid to Glucosinolate Biosynthesis: Protein Sequence
Changes in the Evolution of Methylthioalkylmalate Synthase in Arabidopsis. The Plant Cell, 23, 38-53.
Special enzymes are responsible for catalyzing the synthesis of the side chains found in the
various glucosinolates. Jan-Willem de Kraker
and Jonathan Gershenzon have isolated one of
these enzymes from Arabidopsis thaliana and
discovered a surprising new insight. The enzyme
methylthioalkylmalate synthase (MAM), which
catalyzes glucosinolate formation, strongly resembles an enzyme with a completely different
function: IPMS (isopropylmalate synthase), which
is involved in the synthesis of the amino acid leucine. The scientists found two major structural
differences between IPMS and MAM. The last
120 amino acids in IPMS were absent in MAM,
and in the active site of the enzyme two amino
acids had been exchanged.
IPMS encoding genes are present in eubacteria,
archaebacteria, algae and higher plants, but not
in animals. Therefore, we humans must ingest
leucine as an essential amino acid with our food.
In the model plant Arabidopsis thaliana, IPMS
consists of a chain of 631 amino acids. In actual
enzymes, these amino acid chains, also called
polypeptides, are not straight. Depending on the
sequence of the respective amino acids, chains
are folded into helices, sheets or other shapes
necessary for the polypeptide to perform its biological function. To make sure that enzyme-mediated catalysis does not happen in an uncontrolled
fashion, many enzymes are regulated by a feedback mechanism. In IPMS, this mechanism is located in the last 120 amino acids of the polypeptide chain. As soon as enough leucine is available,
the production of leucine precursors is stopped.
“We found that the missing 120 amino acids not
only inactivate the regulation of enzyme activities, but also change the architecture of MAM
completely,” Jonathan Gershenzon says. The
missing 120 amino acids cause a profound change
in the active site: it expands and becomes able to
bind larger substrates, allowing it to produce new
products: the precursors of glucosinolates.
The researchers came across IPMS when they
were looking for genes involved in glucosinolate
production. In the context of these studies, they
isolated and sequenced the IPMS gene. The scientists assume that after a duplication of the IPMS
DNA sequence millions of years ago, the “twin
DNA” lost the fragment encoding the sequence of
the last 120 amino acids. In the course of evolution, this probably happened when the mustard
family originated. The loss turned out to be very
advantageous for the plants: it enabled them to
produce glucosinolates as a defense against herbivores. The assumptions were confirmed by de
Kraker and Gershenzon in extensive in vitro experiments. The way MAM emerged is probably
typical for the way new phenotypes arise from
the variety of genetic information encoded and
stored in DNA, and offers another example of
how small changes have big consequences, some
of which may lead to the development of new
weapons in the evolutionary arms race between
plants and herbivores.. [JWK, AO, HR]
PULS/CE 17
Research Highlight | Newsletter April 2011
Antibiotics
in situ
Leaf-cutting ants cultivate the fungus Leucoagaricus gongylophorus with harvested leaf material. In turn the fungus garden serves the ants as
themajor food source. However,this symbiosis, is
threatened by invasive fungi, such as Escovopsis
weberi, which can destroy the symbiotic fungus.
In 1999 Currie et al. (Nature, 1999, 398, 701-704)
found that bacterial symbionts on the leaf-cutting
ants’ body support the leaf cutting ants to protect
their fungus garden against harmful fungi invading their nests.
In PULS/CE 13 (2009) we reported that Susanne Haeder and Dieter Spiteller had identified
candicidin macrolides as the first antibiotics from
microbial symbionts of leaf-cutting ants. Candicidin macrolides strongly inhibit the growth of
E. weberi. Because many different bacteria are
found in the ecosystem of leaf-cutting ants, a
vast diversity of antibiotic substances can be expected. Ilka Schoenian from Spiteller’s group now
developed a method to quickly identify further
antibiotics produced by microbial symbionts of
leaf-cutting ants and studied their function in the
leaf-cutting ants’ nests. Together with colleagues
from Dortmund, Kaiserslautern and Panama, the
scientists studied the chemical basis of the synergism and antagonism in microbial communities
in the nests of leaf-cutting ants.
Ilka Schoenian determined the relationship of microbial symbionts from leaf-cutting ants to known
bacteria. Using database search the secondary
metabolite spectrum of these closest relatives
was identified. Such obtained putative candidate
antibiotics of the microbial symbionts from leaf
Microscopic image of an Acromyrmex echinatior leaf-cutting ant (left) and distribution of the antibiotic valinomycin on the ant’s body (right; MALDI Image: green = little, red = high amounts of valinomycin) Images: PNAS
cutting ants were then searched for in extracts
of the microbial symbionts by targeted mass
spectrometric profiling. Thus antimycins A1-A4,
valinomycins and actinomycins were identified
from microbial symbionts of leaf-cutting ants.
Using MALDI imaging it was possible to obtain a
picture of the valinomycin distribution on the ant’s
body. This is the first study that provides evidence
that antibiotic substances are directly present directly on the leaf-cutting ant’s body.
In order to study the ecological function of the
identified antibiotics growth inhibition assays
were performed. Actinomycins for example
inhibited the growth of potentially competing
soil bacteria. Moreover, antibiotic mixtures of
candicdin, antimycin, valinomycin and actinomycin are much more effective than the individual
comounds. Antibiotic mixtures inhibit the growth
of Escovopsis, even if the single components are
below the inhibitory concentration.
Synergistic effect of antibiotics: Single
components (A-E) are hardly effective
in very low concentrations, in combination, however, they inhibit the growth of
Escovopsis (F).
Photo: PNAS
Ilka Schoenian
Photo: MPI-CE
Original Publication:
Further experiments are planned to study the
diversity and functions of antibiotics in the ecosystem of leaf-cutting ants in detail in order to
gain a better understanding of the interplay of
secondary metabolites in nature. The studies
may also lead to the discovery of new antibiotics that could contribute to the fight against
infectious diseases in humans. [JWK, AO, DS]
Schoenian, I., Spiteller, M., Ghaste, M.,
Wirth, R., Herz, H., Spiteller, D. (2011).
Chemical basis of the synergism and
antagonism in microbial communities in the nests of leaf-cutting ants.
Proceedings of the National Academy
of Sciences of the United States of
America, 108, 1955-1960.
PULS/CE 17
16
Newsletter April 2011 | IMPRS Project
Scent of a Poplar
The ability to communicate is essential for all living beings including plants. Plants may not emit
sounds but they are fragrant, and odors are their
language. They emit volatile organic compounds
(VOCs) in response to herbivore attack; VOCs
attract the natural enemies of the herbivores,
such as predators and parasitoids. This process
is known as indirect defense – the plants’ cry for
help.
Gypsy moth larvae are common poplar
pests. Freshly hatched larvae can be
parasitized by Glyptapanteles liparidis
wasps. These tiny parasitoids are
attracted by volatile organic com-
Indirect defenses of trees have been poorly studied in the past. Trees have several special features, such as wood formation, perennial growth
and seasonality, which makes them particularly
interesting and challenging to study.
pounds emitted by attacked trees.
Photo: C. Meyer, Beutenberg Campus
The main objective of my Ph.D. research is to
determine if indirect defenses are functional
mechanisms in the black poplar (Populus nigra).
We are using a model system which involves two
common herbivores of black poplars: gypsy moths
(Lymantria dispar) and poplar hawk moths (Laothoe
populi). The third actor is a tiny parasitic wasp
(Glyptapanteles liparidis), which lays its eggs only
gypsy moth larvae during their early larval stages
; the offspring of the wasp grow and develop inside the small caterpillars, preventing them from
growing and killing them within a few days.
Andrea Liliana Clavijo McCormick
Some of the exciting questions we have asked so
far are: Is the odor emitted by poplar trees different depending on which herbivore is attacking or
even according to the larval stage of the gypsy
moth? Can the wasps smell whether the plant is
being damaged by their potential host (the gypsy
moth) or a non-host species, and whether gypsy
moth larvae are still in their early larval stage?
from Colombia holds a fellowship of
the International Max Planck Research
School. Her PhD project in the Department of Biochemistry (project group
of Dr. Sybille Unsicker) focuses on
volatile-mediated indirect defenses of
poplar.
Photo: MPI-CE
After analyzing and comparing the odors of poplar
trees emitted following herbivory by the two different moth species and by two different larval
stages of the gypsy moth, we identified over 30
different chemical compounds. Interestingly, the
odor blends differed not in composition, only in
amount. The next step was to expose single compounds to the wasp’s antennae to observe if they
caused physiological responses; for this we used
a method called electroantennographic detection.
Out of a set of 20 compounds, we observed physiological responses for at least 10.
These results suggest that poplars produce different odors depending on who is attacking them
and that the wasp’s antennae can perceive some
of the compounds which are differentially emitted upon different types of damage. However,
many other questions remain to be answered,
such as the effect of single compounds on the
wasp’s behavior (attractant or repellant); whether behavioral effects are a result of individual
compounds or blend ratios; and ultimately, if this
indirect defense mechanism works under natural
conditions.
A. McCormick
PULS/CE 17
News | Newsletter April 2011
10th IMPRS PhD Symposium – more participants than ever
The annual symposium of the International Max
Planck Research School at the old castle (Altes
Schloss) in Dornburg is becoming an increasingly
important event. It provides scientific exchange not
only between PhD students, but also between the
scientific departments of the MPI and the participating institutes of Friedrich Schiller University.
More than 120 PhD students, supervisors and postdocs attended the symposium, the highest number
of participants ever. 24 PhD students presented
their projects in talks, 33 presented posters. Both
posters and talks were intensively discussed.
Bill Hansson Elected to the
Royal Swedish Academy of
Sciences
The Royal Swedish Academy of Sciences in
Stockholm has elected Prof. Bill S. Hansson as
a member of the “class for biosciences”. The
society, which also awards the Nobel Prizes each
year, was founded in 1739 as an independent nongovernmental scientific society and currently has
at the MPI
What role do enzymes play in insects’ defense
against plant toxins? How can DNA be made visible? Am I what I eat? These were some of the
questions that were addressed in the hands-on
workshops the MPI organized for school kids
at the “Forsche-Schüler-Tag” on April 14, 2011.
28 girls and 19 boys from 8 th grade on visited the
Two lectures by invited speakers completed the
program: Dr. Corné Pieterse, University of Utrecht, Netherlands, talked about plant hormones and
defense, and Dr. Martin Heil, CINVESTAV Mexico,
reported on the role of ants in indirect plant defenses.
At the 10 th IMPRS symposium prizes
The symposium is an important part of the PhD
training offered by the IMPRS and provides a familiar and at the same time critical environment
where PhD students can present their research
results, answer questions, or lead sessions professionally. Karin Groten
were awarded for the best talks and
posters. The awardees (from left to
right): Maria Heinrich, Andrea McCormick, and Elisabeth Eilers.
Photo: Angela Overmeyer, MPI-CE
about 400 members. World-famous botanist and
zoologist Carl Linnaeus (1707-1778), the father of
modern taxonomy and considered by many to be
one of the fathers of modern ecology, was one of
its founders.
The induction ceremony took place during the annual meeting of the academy on March 31, 2011,
in Stockholm. [AO]
Bill Hansson during the induction
ceremony into the Royal Swedish
Academy. Foto: Markus Marcetic, KVA
institute this year. Among the experiments they
performed in the labs: analyses of their fingernails
in the isotope ratio mass spectrometer; comparisons between natural and synthetic odors by
means of GC/MSl; and tests with bees and ants
using a confocal microscope. We hope that a lot
of interest in and fascination with research was
stimulated in the participants. We are already
looking forward to April 26, 2012, when the motto
will again be: “Looking for young researchers!”
Angela Overmeyer
The Forsche-Schüler-Tag provides an
opportunity for girls and boys to get a
glimpse of scientific methods.
Photo: Angela Overmeyer, MPI-CE
PULS/CE 17
Newsletter April 2011 | News & Events
XVI Int. Symposium on Olfaction and Taste
Stockholm, Sweden, 23.-27. Juni 2012
http://www.isotxvi.com
MPI-CE Institute Symposium and Alumni Meeting
The annual institute symposium of the Max Planck Institute for Chemical Ecology will be held on
September 22-23, 2011, in Lecture Hall 3, Friedrich Schiller University Jena, Carl-Zeiß-Straße 3, 07743
Jena. All former co-workers and alumni of the institute will be specifically invited this year.
www.ice.mpg.de
Impressum: PULS/CE is published semi-annually and can be downloaded free of charge on the homepage of the MPI for
Chemical Ecology and is distributed electronically as PDF to subscribers. A print version will be sent on request.
Editor: MPI-CE, Jena • Managing Director: Prof. Dr. Bill S. Hansson (viSdP). Editorial Staff: Dr. Jan-W. Kellmann,
Research Coordination • Angela Overmeyer, M.A., Information and Communication • Emily Wheeler, Editing
ISSN: 2191-7507 (Print), 2191-7639 (Online)