Báo cáo khoa học: Plant oxylipins: Plant responses to 12-oxo-phytodienoic acid are governed by its specific structural and functional properties ppt

Plant oxylipins: Plant responses to 12-oxo-phytodienoic acid are governed by its specific structural and functional properties Christine Bo¨ttcher1and Stephan Pollmann2 1 CSIRO Plant Ind

Plant oxylipins: Plant responses to 12-oxo-phytodienoic acid are governed by its specific structural and functional properties

Christine Bo¨ttcher1and Stephan Pollmann2

1 CSIRO Plant Industry, Adelaide, Australia

2 Department of Plant Physiology, Ruhr-University Bochum, Germany

Introduction

Plants are permanently exposed to a multitude of

var-iable environment cues, and thus have to cope with

changes in, for example, temperature, light quality,

exposure to UV light, mechanical forces and water

availability, as well as osmotic stress, wounding and

pathogen challenges [1–8] Over time, plants have

evolved several physical barriers as defensive

weap-ons, i.e the cuticula, thorns and stinging hairs, as

well as constitutively expressed toxic compounds or

enzymes In addition to these morphological adapta-tions, plants have established inducible systems Despite the fact that plants possess neither an immune system nor a nervous system like animals, they are able to defeat herbivore and pathogen preda-tors and respond to changes in their environment using highly complex inducible defense⁄ response mechanisms These systems require the perception of external stress conditions, transformation of these

Keywords

12-oxo-phytodienoic acid;

cyclo-oxylipin-galactolipids; environmental stress;

jasmonates; jasmonic acid;

mechanotransduction; oxylipins;

phytoprostanes; plant stress responses;

transcriptional regulation

Correspondence

S Pollmann, Department of Plant

Physiology, Ruhr-University Bochum,

Universitaetsstrasse 150, D-44801 Bochum,

Germany

Fax: +49 234 321 4187

Tel: +49 234 322 4294

E-mail: stephan.pollmann@

ruhr-uni-bochum.de

(Received 7 November 2008, revised 23

March 2009, accepted 31 March 2009)

doi:10.1111/j.1742-4658.2009.07195.x

One of the most challenging questions in modern plant science is how plants regulate their morphological and developmental adaptation in response to changes in their biotic and abiotic environment A comprehen-sive elucidation of the underlying mechanisms will help shed light on the extremely efficient strategies of plants in terms of survival and propagation

In recent years, a number of environmental stress conditions have been described as being mediated by signaling molecules of the oxylipin family

In this context, jasmonic acid, its biosynthetic precursor, 12-oxo-phytodie-noic acid (OPDA), and also reactive electrophilic species such as phyto-prostanes play pivotal roles Although our understanding of jasmonic acid-dependent processes and jasmonic acid signal-transduction cascades has made considerable progress in recent years, knowledge of the regula-tion and mode of acregula-tion of OPDA-dependent plant responses is just emerg-ing This minireview focuses on recent work concerned with the elucidation

of OPDA-specific processes in plants In this context, aspects such as the differential recruitment of OPDA, either by de novo biosynthesis or by release from cyclo-oxylipin-galactolipids, and the conjugation of free OPDA are discussed

Abbreviations

cGL, cyclo-oxylipin-galactolipid; dnOPD, dinor-OPDA; GSH, glutathione; GST, glutathione S-transferase; JA, jasmonic acid; LOX,

lipoxygenase; Me-JA, methylester of JA; OPDA, 12-oxo-phytodienoic acid; RES, reactive electrophilic species; TGA, TGACG motif-binding factor.

stimuli into internal signals, and as a consequence, an

appropriate adjustment of gene expression via specific

signal-transduction cascades in answer to the altered

environment

With regard to inducible response mechanisms of

plants and animals, compounds derived from the

metabolism of polyunsaturated fatty acids, collectively

termed oxylipins or octadecanoids, play a crucial role

In mammals, oxylipins derive mainly from arachidonic

acid, a fourfold unsaturated C20 fatty acid, and have

pivotal functions in the inflammatory process, in

gen-eral reactions to infections and in allergic responses

[9] By contrast, phytooxylipins derive mainly from

oxygenized C16 and C18 fatty acid precursors Much

recent research has focused on the analysis of these

compounds The biosynthesis of most plant oxylipins

is initiated by the action of lipoxygenases (LOX),

which are capable of introducing molecular oxygen at

either the C9 or C13 position of the C18 fatty acids

linoleic acid (18:2) and a-linolenic acid (18:3),

respec-tively [10,11] Plants possess a number of different

LOX isoforms that can be subdivided into two groups:

type 1, containing all 9-LOX isoenzymes, which are

exclusively found outside the plastids; and type 2,

including all plastid-localized isoenzymes, such as the

13-LOXs [12,13] Numerous biochemical studies

pro-vide epro-vidence that the hydroperoxy reaction products

of LOX-assisted catalysis lead to a plethora of

differ-ent oxylipins, i.e hydroxy, epoxy or divinylether fatty

acids, as well as volatile aldehydes and alcohols and

the well-established wound hormones jasmonic acid

(JA), 12-oxo-phytodienoic acid (OPDA), dinor-OPDA

(dnOPDA), traumatic acid and traumatin [4,14]

More-over, a-dioxygenases catalyze the enantioselective

2-hy-droperoxidation of long-chain fatty acids, giving rise

to additional oxylipins also involved in pathogen

defense [15,16]

In recent years, the main concern has been with the

13-LOX reaction, which initiates the synthesis of

octa-decanoids (Fig 1), a compound class comprising

jasm-onates such as JA and several JA derivatives like

tuberonic acid, a 12-hydroxy analog of JA, and their

precursors, for example, the biological active OPDA

The biosynthesis of JA, and activation of the

interme-diates by generation of the corresponding CoA esters

for b-oxidation, is deemed to be basically uncovered

with respect to the enzymes involved (for a review see

Ref [7])

In 1980, the senescence-promoting activity of the

methyl ester of JA (Me-JA) was first described for

leaves and shoots of Artemisia [17], followed by

publi-cations on the growth-inhibiting physiological role of

JA in higher plants [18,19] Since then, lots of evidence

has been provided for the involvement of this phyto-hormone in either mechanotransduction [20], the response to osmotic stress [21], UV damage [22] and water stress [23], or as a defense to wounding [24,25]

In particular, with regard to insect attacks [26,27] and infections with necrotrophic fungi [28–30], respectively,

JA has been shown to play a key role Furthermore, essential developmental processes, such as seed matu-ration [31,32], pollen development [33] and anther dehiscence [34] are linked to variations in endogenous

JA levels

Multiple gemone-wide transcript-profiling appro-aches, utilizing differential experimental set-ups and several corresponding Arabidopsis mutants have under-scored the essential role of OPDA and JA [35] Partic-ularly, the fad3⁄ 2fad7 ⁄ 2fad8 (fatty acid desaturase) triple mutant that is unable to produce the JA precur-sor a-linolenic acid [33] and the coi1 (coronatine insen-sitive) JA signal transduction mutant [36] have revealed considerably decreased resistance towards the herbivore Bradysia impatiens and the necrotrophic fungus Alternaria brassicicola Based on these results and the JA deficiency of two null alleles in the OPR3 locus, namely opr3 [37] and dde1 (delayed dehiscence) [38], it seemed surprising that these mutants exhibited

no altered resistance towards herbivore and pathogen challenge Recently, it has been reported that octadeca-noid-dependent growth inhibition is seemingly medi-ated by JA rather than OPDA Consecutive treatment

of opr3 with OPDA resulted in unaffected leaf areas, whereas in OPDA- or Me-JA-treated wild-type plants, leaf areas were significantly reduced By contrast, opr3 mutants infested with B impatiens larvae were able to survive the attack, whereas in the aos mutant the pop-ulation was reduced to 4% [39] This moved OPDA center stage, and it appears to be a good candidate for

an independent signaling molecule specifically mediat-ing resistance towards biotic foes

Physiological processes mediated by OPDA

Several physiological processes are known to be like-wise stimulated by overlapping activities of OPDA and

JA In addition, OPDA has been described in JA-inde-pendent responses Emphasizing its involvement in mediating resistance to pathogens and pests, OPDA is assumed to be the primary signal transducer in the elicitation process [40], because OPDA strongly induces alkaloid biosynthesis in Eschscholtzia californica cell cultures Furthermore, tendril coiling of Bryonia dioica

is more responsive to OPDA than JA Although exogenously administered JA is capable of promoting

tendril coiling, the concentration needed to elicit the

reaction is one order of magnitude higher than with

methyl-OPDA and exhibits a slower kinetic In

addi-tion, JA levels remain lower in mechanoreacting

ten-drils than in those of cis-(+)-OPDA and increase only

late during the coiling process Comparable results

have been obtained in Phaseolus vulgaris

thigmomorphogenesis In these studies, JA levels

remained below the detection limit after mechanical

stimulation Thus, OPDA can be considered as an

endogenous signal transducer of Br dioica and P vul-garis mechanotransduction (Fig 2) [20,41–43] In this regard, OPDA and JA signaling is perhaps linked with

Ca2+ signaling It has recently been reported that OPDA, as well as JA, induces transient Ca2+ signals

in both the cytosol and the nucleus of a stimulated transgenic tobacco cell culture By contrast, JA–Ile treatment had no detectable effect on the cellular

Ca2+content of the examined cell culture system [44] Although OPDA and JA both contribute to an

Fig 1 JA biosynthesis and OPDA metabolism in A thaliana 13-LOX, 13-lipoxygenase; ACX, acyl-CoA oxidase; AOC, allene oxid cyclase; AOS, allene oxid synthase; CTS ⁄ PXA1 ⁄ PED3, ABC transporter for OPDA or OPDA–CoA import; COI1, F-box protein in JA signal transduc-tion; GST, glutathione S-transferase; KAT, L -3-ketoacyl-CoA thiolase; MFP, multifunctional protein; OPR, 12-oxo-phytodienoate reductase; PLAI, plastidic acyl hydrolase.

increase in the free cellular calcium level, it has been

shown that the response to OPDA was much quicker

(< 30 s) and the response amplitude higher (1 lm)

than in the response to JA treatment This may be

indicative of distinct regulatory functions for the two

compounds In terms of tendril coiling, the

octadeca-noid-dependent alteration in the Ca2+ content may

induce ion fluxes, thereby directly affecting the turgor pressure, or regulate the transcription of a specific sub-set of genes (Fig 2) [45,46] Intriguingly,

Medica-go truncatula has recently been reported to respond very sensitively to mechanostimulation with enhanced

JA levels and altered accumulation of AOC transcripts [47] Unfortunately, this study did not monitor other genes involved in JA biosynthesis or cis-(+)-OPDA levels during the reaction It will be exciting to learn whether mechanotransduction in Medicago is mediated

by JA rather than by OPDA

Even though nyctinastic leaf movement most likely differs mechanistically from mechanostimulated tendril coiling, work conducted on the nyctinasty of several plant species, such as Albizzia, has emphasized that JA derivatives, i.e potassium b-d-glucopyranosyl 12-hy-droxyjasmonate, may at least contribute to this distinct type of plant movement In particular, nyctinastic leaf closing is mediated by potassium b-d-glucopyranosyl 12-hydroxyjasmonate In the case of nyctinasty, it is suggested that the biochemical factors accounting for leaf closing and opening directly affect K+ channel activity, thereby modulating turgor pressure in special-ized flexor cells [48–50]

By analyzing a rice mutant with an impaired light response, hebiba, it has recently been shown that oxylipins are also involved in phototropic coleoptile bending Further experiments have emphasized an auxin-antagonistic impact of JA in gravitopic reac-tions It is suggested that the JA gradient that is formed in reciprocal orientation to the indole-3-acetic acid gradient in coleoptiles inhibits growth in places where it is already poorly promoted by indole-3-acetic acid Thereby, the velocity of the gravitopic movement

is seemingly accelerated [51–54] The majority of the effects described by the Nick group are most likely not OPDA specific, but rather mediated by JA However, intriguingly, the authors described an OPDA gradient which accompanies the JA gradient in the opposite direction during gravitopism This has been interpreted

as a putative second level of regulation in a late step establishing the JA gradient Extending this previous interpretation, it is tempting to speculate that this may also be indicative of OPDA-specific, JA-independent regulatory effects In the conducted experiments, an independent signaling function of OPDA was not taken into account and thus cannot be ruled out Extending the previous functions, OPDA and⁄ or 16:3 fatty acid-derived dnOPDA are discussed as inhibitors of programmed cell death in the conditional Arabidopsis flu mutant [55] Upon a dark-to-light shift,

flumutants generate singlet oxygen (1O2) in their plast-ids This non-radical reactive oxygen species accounts

Fig 2 Schematic representation of stress-induced processes

med-iated by reactive electrophilic species, such as phytoprostanes and

OPDA, and jasmonic acid as well as by its bioactive amino acid

conjugate, jasmonoyl–isoleucine

for growth inhibitory effects and the development of

necrotic lesions [56] Studies on flu and the flu⁄ dde2-2

double mutant indicated that OPDA and⁄ or dnOPDA

promote the inhibition of programmed cell death

pro-cesses induced by 1O2, and the well-known cell death

induction by JA was suppressed Unexpectedly,

com-parison of flu and the flu⁄ dde2-2 double knockout,

impaired in OPDA, dnOPDA and JA production,

showed that the concurrent absence of those

com-pounds restored the wild-type sensitivity of flu to cell

death Hence, OPDA and⁄ or dnOPDA are seemingly

necessary and able to antagonize JA-promoted effects

on cell death (Fig 2) (for more detail, refer to the

minireview by Reinbothe et al [56a])

A proposed mechanism of OPDA action

Despite being processed by the SCFCOI1–JAZ–MYC

complex (for more detail, refer to the minireview by

Chini et al [56b]), the major regulatory effect of

OPDA on the transcriptional machinery is determined

by its remarkable structural properties Oxylipins with

a,b-unsaturated keto or epoxy functions can behave

like reactive electrophilic species (RES) towards

cellu-lar nucleophiles [57] In this regard, a,b-unsaturated

keto groups can participate in nucleophilic Michael

additions in which carbanions are added to

a,b-unsatu-rated carbonyl compounds This type of addition

reac-tion to proteins or to the tripeptide glutathione (GSH)

may cause changes in protein activity or in the cellular

redox state, which, in turn, can influence gene

expres-sion [58–60] Such interactions have been described for

OPDA and a variety of related compounds [61–63]

Although the enzymatic production and physiological

impact of the octadecanoid-phytohormones OPDA

and JA is well-known (Fig 1), the nonenzymatic

gen-eration of structurally related compounds and their

role in cellular stress responses is a very intriguing and

challenging matter of actual research The latter

com-pounds comprise oxidized lipids and lipid fragments,

many of which are derived in vivo from a-linolenic acid

[64] They range from very small compounds such as

malondialdehyde [65,66], to more complex families of

hydroxy fatty acids and phytoprostanes [67–69]

Cur-rently, it is assumed that omega 3 fatty acids, in

partic-ular a-linolenic acid, serve in the protection of cells by

absorbing reactive oxygen species such that they are

oxidized in a free-radical-dependent manner [70] This

trienoic fatty acid-mediated consumption of reactive

oxygen species results in the nonenzymatic generation

of oxidized polyunsaturated fatty acids and the

subse-quent production of many RES [71] Recent work on

the impact of cyclopentenone-oxylipins, i.e OPDA

and A1-phytoprostane (Fig 2), on the proteome of Arabidopsis leaves provides evidence for the induction

of both classical stress proteins and enzymes connected

to cellular redox and detoxification systems by those compounds Notably, a large portion of the identified candidate proteins are located in plastids Given the fact that the two utilized oxylipins are generated in these organelles, one may suggest that direct alteration

of enzyme activity⁄ specificity or direct influencing of the degradation of target proteins, triggered by enzy-matically or nonenzyenzy-matically generated RES, may take place in chloroplasts [72]

In mammals, the structural requirement for activity

of cyclopentenone prostaglandins, including effects on gene expression, is already known to be determined by their a,b-unsaturated carbonyl groups [73] Hydroper-oxy arachidonic acids, like leukotriene C4and 5-oxo-7-glutathionyl-8,11,14-eicosatrienoic acid, are further examples of such biologically active RES, which can modulate the chemotaxis of neutrophiles and actin polymerization, respectively [74] Moreover, in animals, covalent binding of RES is an appropriate tool with which to regulate transcription factor activity, as shown for nuclear factor kappa-light-chain-enhancer

of activated B cells (NF-jB), c-Jun or peroxisome pro-liferator-activated receptor (PPARc) [75–77] However, experimental evidence for a covalent linkage between RES and any specific protein in planta is yet to be pro-vided Nevertheless, both the examples from animals and work on phytoprostanes allow for hypotheses in which bioactive plant RES act as Michael acceptors, thereby adding not only to GSH, but also directly to enzymes and transcription factors

OPDA: an independent regulator of gene expression

Given the functional and structural differences between OPDA and JA, it is exciting to presume that OPDA is specifically able to orchestrate the expression of a sub-set of genes, independent of those influenced by JA

To identify such genes, and thus speculate on the phys-iological impact of their gene products, several micro-array approaches, using mainly the opr3 null mutant, have been conducted By analyzing a set of 150 defense-related genes, two general conclusions were drawn First, the COI1 signal transduction pathway can be activated by both OPDA and JA Second, com-plete activation of the wound response needs the joint action of OPDA and JA Furthermore, not all COI1-dependent genes were induced in wounded or OPDA-treated opr3 plants, but both treatments activated the transcription of several COI1-independent genes, which

were not influenced by JA [78] More recently, a

genome-wide microarray experiment identified a set of

> 150 genes that were induced by exogenously applied

OPDA, but not by JA or Me-JA [79] The majority of

the identified genes encode for proteins involved in

stress responses, for example, heat shock proteins,

glutathione S-transferases (GSTs) or polypeptides

related to signal transduction, such as transcription

factors and kinases In addition, genes encoding for

enzymes involved in the modulation of cellular

indole-3-acetic acid levels, such as ILR1, IAR3 and ILL5,

suggest a tight connection between stress responses

and auxin metabolism Intriguingly, a further study

aimed at analyzing the molecular bases of

phytopros-tane activity, underlines that the regulation of gene

expression by those compounds is seemingly similar to

the regulation by OPDA and pathogens [63]

More-over, a major part of these responses is shown to be

dependent on TGACG motif-binding factor (TGA)

transcription factors Thus, a specific interaction of

RES, such as OPDA or nonenzymatically formed

phy-toprostanes, with TGA transcription factors seems

plausible and is reminiscent of the mentioned situation

in animals (vide ante)

However, unless direct covalent binding between

RES and any transcription factor has been proven

experimentally, the function of RES may also be more

indirect; acting through regulation of the cellular redox

state Work conducted in the Pieterse lab underscores

the tight connection between plant defense responses

and the redox state of the cell [80,81] For example, the

salicylic acid-induced antagonistic effect on

JA-respon-sive gene expression is facilitated by the modulation of

cellular GSH levels The transcriptional regulator,

NPR1, undergoes conformational changes in response

to alterations in the cellular redox state [82] Under

sys-temic acquired resistance conditions, NPR1 oligomers

are reduced to monomers, thereby allowing efficient

uptake into the nucleus where NPR1 can develop its

gene-regulatory functions Because of the lack of

DNA-binding domains in NPR1, it is suggested that

the protein acts through protein–protein interaction

with transcription factors Indeed, in multiple yeast

two-hybrid screens, an interaction between NPR1 and

a TGA subclass of basic leucine-zipper transcription

factors has been emphasized [83,84] Taking into

account that oxylipins effectively induce TGA

tran-scription factor expression, it is attractive to speculate

that, as yet undetected, NPR1-like transcriptional

regu-lators are also involved in the redox-dependent

trans-mission of oxylipin signals

Very recently, PHO1;H10, a member of the PHO1

gene family of Arabidopsis thaliana, has been described

as being transcriptionally regulated by OPDA, but not

by JA or coronatine, a bacterial polyketide metabolite that mimics JA–Ile [85] PHO1;H10 expression is strongly induced by a variety of stresses, including responses to wounding and dehydration The corre-sponding gene product is involved in loading inorganic phosphate into the xylem in roots Excitingly, PHO1;H10 induction by wounding, as well as OPDA treatment, made use of the COI1-dependent pathway, which is noteworthy in that there is currently no exper-imental evidence that OPDA can act via the SCFCOI1– JAZ–MYC-complex [86] (see minireview by Chini

et al [56b]) However, these results suggest that dis-tinct signaling cascades may emerge from the SCFCOI1 complex, depending on the presence of either OPDA

or JA

Regulating the pool of free OPDA by conjugation

Cell injury, for example, by pathogen attack is, in most cases, accompanied by oxylipin bursts These drastic increases in cellular oxylipin content, governed

by enzymatic or nonenzymatic de novo production or

by the release of oxylipins from storage compounds (vide infra) go hand in hand with the considerable cell toxicity of these compounds Rapid trapping and sequestration of the partially toxic compounds could prevent unintended cell damage In this connection, animals have evolved mechanisms for the rapid detoxi-fication of oxylipins, e.g by the addition of intracellu-lar thioredoxin [87] With respect to recently presented data, it seems as though the conjugation and thereby inactivation of free signaling molecules is a common feature not only of animals, but also of plants OPDA and phytoprostanes are functionally inactivated by the GST-catalyzed addition of GSH [63,72] In underlying studies, numerous GST genes were found to be upreg-ulated by OPDA One, a predicted chloroplastic GST (GST6, At2g47730), is described as being able to cata-lyze the conjugation of OPDA to GSH This finding, however, corresponds to work conducted in our labo-ratory, in that we identified and characterized three OPDA-induced cytoplasmic GSTs of the tau family [88], all capable of adding OPDA, as well as trauma-tin, to GSH in vitro (C Bo¨ttcher et al., unpublished data) Based on publicly available microarray data, the expression of all of these GSTs responds strongly to numerous stresses, e.g wounding, jasmonate treat-ment, nutrient starvation and fungal infections Corre-sponding OPDA–GSH conjugates have been reported

to accumulate in cryptogein-treated tobacco plants [62], the fate of such membrane-impermeable GSH

adducts in plants remains unclear Nevertheless, it may

be suggested that the addition of RES to GSH renders

them inactive or modulates their biological impact In

addition to GST induction, the transcription of lipid transfer proteins is strongly induced in answer to vari-ous biotic and abiotic stresses Such lipid transfer

Fig 3 Structures of the currently identified cyclo-oxylipin-galactolipids from Arabidopsis thaliana.

proteins have already been reported as a potential

oxy-lipin scavenger [89], although addition of OPDA or

bioactive phytoprostanes has yet to be explored

In conclusion, the results point to a scenario in

which RES trigger both the regulation of a specific

cluster of genes and their own inactivation by a

feed-back loop, inducing the expression of detoxification

enzymes such as GSTs and lipid transfer proteins

OPDA can be released from

cyclo-oxylipin-galactolipids

Cyclic oxylipins do not occur exclusively in their free

form Rather, the major portion of these compounds,

at least in Arabidopsis and some near relatives, is

found covalently bound to galactolipids in the

thyla-koid membrane [90–95] (Fig 3) The occurrence of

lipid-bound cyclic oxylipins is currently assumed to be

a special trait of only a very few members of the

Brassicaceae Recently, we were able to detect

lipid-bound cyclic oxylipins in Arabidopsis arenosa,

Arabid-opsis halleri, ArabidArabid-opsis petraea, ArabidArabid-opsis thaliana,

Arabis pendula, Camelina microcarpa, Capsella rubella

and Neslia paniculata, all members of the Brassicaceae,

but not in 16 species taken from 11 other families [96]

The amount of these esterified oxylipins, collectively

termed cyclo-oxylipin-galactolipids (cGL), is not

con-stant but responds to external stimuli Upon

wound-ing, for example, cGL levels in the thylakoids increase

[90,97] Furthermore, senescence-promoting effects

have been described for arabidopside A (Fig 3), a

monogalactosyldiacylglycerol species carrying OPDA

at sn1 and dnOPDA at sn2 [98] Furthermore growth

inhibitory effects have been reported for

monogalacto-syldiacylglycerol-O, arabidopside A, B and F (Fig 3)

[94] Recent work also linked levels of lipid-bound

OPDA and dnOPDA with responses to pathogen

challenge, attributing antimicrobial activity to the

trioxylipin-containing monogalactosyldiacylglycerol

de-rivatives, arabidopside E and G (Fig 3), which were

further shown to accumulate in response to

dexameth-asone-induced expression of an antivirulence protein

[93,95] The biosynthesis of lipid-bound oxylipins is,

however, not yet fully understood, but several lines of

evidence emphasize a direct conversion of lipid-bound

polyunsaturated fatty acids into oxylipins [93]

How-ever, the oxylipins linked to the galactosyl-moieties in

arabidopside E and G, at least, have to be covalently

linked to the molecules by transacylations From this,

a general involvement of transacylation reactions,

introducing oxylipins into galactolipids, cannot be

excluded beyond reasonable doubt Likewise, the

par-ticipation of enzymes of the jasmonate biosynthetic

pathway in the production of esterified cyclo-oxylipins

is yet to be discovered Given that the majority of OPDA and dnOPDA is found trapped in galactolipids, there is speculation about the function of cGL as a storage form for reactive oxylipins and that an alterna-tive free fatty acid-independent pathway exists for the synthesis of oxylipins Consistent with the former hypothesis, the lipolytic release of oxylipins from sev-eral cGLs has already been reported [99] Moreover, there is an indication that cGLs may serve as sub-strates for JA biosynthesis Recently, a plastidic acyl hydrolase has been identified that preferentially cata-lyzes the hydrolyzation of cGLs (Fig 1) and confers resistance to Botrytis cinerea [100] Intriguingly, the plaI knockout mutant exhibited an expected enhanced susceptibility to the necrotrophic fungus, without affecting wound-induced JA accumulation In fact, this invites the presumption that lipid-bound and free pools

of oxylipins are differentially recruited depending on the particular stimulus, which extends the current pic-ture of inducible defense⁄ response systems in planta

Conclusions

In Arabidopsis, the majority of cyclic oxylipins are not found the free form, but rather are covalently bound

to galactolipids Under certain circumstances, the oxy-lipins can be released from these lipids by lipases Regardless of their origin, in both plants and animals, RES are engaged in the activation of a distinct set of mostly defense- and stress-related genes Transcrip-tional regulation is possibly arranged by adding the RES to certain transcription factors, thereby modulat-ing their activity It will be intrigumodulat-ing to discover whether these strikingly similar regulation mechanisms are the result of convergent evolution or whether they constitute an ancient, conserved regulation mechanism that is common to all beings

Acknowledgements The authors are grateful to Professor Dr Elmar W Weiler and Dr Florian Schaller for several fruitful dis-cussions Furthermore, the authors thank Professor

Dr Eckhard Hofmann for critical comments on the manuscript This work was funded by grants from the Deutsche Forschungsgemeinschaft (DFG), Bonn SFB480⁄ A10 and PO1214 ⁄ 3-2 for SP

References

1 Browse J (2005) Jasmonate: an oxylipin signal with many roles in plants Vitam Horm 72, 431–456

2 Lorenzo O & Solano R (2005) Molecular players

regu-lating the jasmonate signalling network Curr Opin

Plant Biol 8, 532–540

3 Schaller F, Schaller A & Stintzi A (2005) Biosynthesis

and metabolism of jasmonates J Plant Growth Regul

23, 179–199

4 Schilmiller AL & Howe GA (2005) Systemic signaling in

the wound response Curr Opin Plant Biol 8, 369–377

5 Delker C, Stenzel I, Hause B, Miersch O, Feussner I &

Wasternack C (2006) Jasmonate biosynthesis in

Arabidopsis thaliana– enzymes, products, regulation

Plant Biol (Stuttg) 8, 297–306

6 Wasternack C, Stenzel I, Hause B, Hause G, Kutter C,

Maucher H, Neumerkel J, Feussner I & Miersch O

(2006) The wound response in tomato – role of

jasmonic acid J Plant Physiol 163, 297–306

7 Wasternack C (2007) Jasmonates: an update on

biosyn-thesis, signal transduction and action in plant stress

response, growth and development Ann Bot (Lond)

100, 681–697

8 Balbi V & Devoto A (2008) Jasmonate signalling

net-work in Arabidopsis thaliana: crucial regulatory nodes

and new physiological scenarios New Phytol 177, 301–

318

9 Smith T, McCracken J, Shin YK & DeWitt D (2000)

Arachidonic acid and nonsteroidal anti-inflammatory

drugs induce conformational changes in the human

prostaglandin endoperoxide H2synthase-2

(cyclooxy-genase-2) J Biol Chem 275, 40407–40415

10 Feussner I & Wasternack C (2002) The lipoxygenase

pathway Annu Rev Plant Biol 53, 275–297

11 Liavonchanka A & Feussner I (2006) Lipoxygenases:

occurrence, functions and catalysis J Plant Physiol 163,

348–357

12 Schewe T (1998) Basic functions of lipoxygenases and

their products in higher plants In Eicosanoids and

Related Compounds in Plants and Animals(Rowley AF,

Ku¨hn H & Schewe T eds), pp 133–150 Princeton

University Press, Princeton, NJ

13 Hildebrand DF, Fukushige H, Afitlhile M & Wang C

(1998) Lipoxygenases in plant development and

senes-cence In Eicosanoids and Related Compounds in Plants

and Animals (Rowley AF, Ku¨hn H & Schewe T eds),

pp 151–181 Princeton University Press, Princeton, NJ

14 Vellosillo T, Martinez M, Lopez MA, Vicente J,

Cas-con T, Dolan L, Hamberg M & Castresana C (2007)

Oxylipins produced by the 9-lipoxygenase pathway in

Arabidopsisregulate lateral root development and

defense responses through a specific signaling cascade

Plant Cell 19, 831–846

15 Hamberg M, Sanz A & Castresana C (1999)

a-Oxida-tion of fatty acids in higher plants Identificaa-Oxida-tion of a

pathogen-inducible oxygenase (piox) as an

a-dioxygen-ase and biosynthesis of 2-hydroperoxylinolenic acid

J Biol Chem 274, 24503–24513

16 Hamberg M, Ponce de Leon I, Rodriguez MJ & Castresana C (2005) a-Dioxygenases Biochem Biophys Res Commun 338, 169–174

17 Ueda J & Kato J (1980) Isolation and identification of

a senescence-promoting substance from wormwood (Artemisia absinthium L.) Plant Physiol 66, 246–249

18 Dathe W, Ro¨nsch H, Preiss A, Schade W, Sembdner

G & Schreiber K (1981) Endogenous plant hormones

of the broad bean, Vicia faba L (-)-jasmonic acid, a plant growth inhibitor in pericarp Planta 153, 530– 535

19 Yamane H, Takagi H, Abe H, Yokota T & Takahashi

N (1981) Identification of jasmonic acid in three species

of higher plants and its biological activities Plant Cell Physiol 22, 689–697

20 Falkenstein E, Groth B, Mitho¨fer A & Weiler EW (1991) Methyljasmonate and a-linolenic acid are potent inducers of tendril coiling Planta 185, 316–322

21 Parthier B (1991) Jasmonates, new regulators of plant growth and development: many facts and few hypothe-ses on their actions Bot Acta 104, 446–454

22 Conconi A, Smerdon MJ, Howe GA & Ryan CA (1996) The octadecanoid signalling pathway in plants mediates a response to ultraviolet radiation Nature

383, 826–829

23 Moons A, Prinsen E, Bauw G & van Montagu M (1997) Antagonistic effects of abscisic acid and jasmo-nates on salt stress-inducible transcripts in rice roots Plant Cell 9, 2243–2259

24 Creelman RA, Tierney ML & Mullet JE (1992) Jas-monic acid⁄ methyl jasmonate accumulate in wounded soybean hypocotyls and modulate wound gene expres-sion Proc Natl Acad Sci USA 89, 4938–4941

25 Albrecht T, Kehlen A, Stahl K, Kno¨fel HD, Sembdner

G & Weiler EW (1993) Quantification of rapid, tran-sient increases in jasmonic acid in wounded plants using a monoclonal antibody Planta 191, 86–94

26 Howe GA, Lightner J, Browse J & Ryan CA (1996) An octadecanoid pathway mutant (JL5) of tomato is com-promised in signaling for defense against insect attack Plant Cell 8, 2067–2077

27 McConn M, Creelman RA, Bell E, Mullet JE & Browse J (1997) Jasmonate is essential for insect defense in Arabidopsis Proc Natl Acad Sci USA 94, 5473–5477

28 Vijayan P, Shockey J, Le´vesque CA, Cook RJ & Browse J (1998) A role for jasmonate in pathogen defense of Arabidopsis Proc Natl Acad Sci USA 95, 7209–7214

29 Staswick PE, Yuen GY & Lehman CC (1998) Jasmo-nate signaling mutants of Arabidopsis are susceptible to the soil fungus Pythium irregulare Plant J 15, 747–754

30 Penninckx IA, Thomma BP, Buchala A, Me´traux JP & Broekaert WF (1998) Concomitant activation of jasmo-nate and ethylene response pathways is required for

induction of a plant defensin gene in Arabidopsis Plant

Cell 10, 2103–2113

31 Creelman RA & Mullet JE (1995) Jasmonic acid

distri-bution and action in plants: regulation during

develop-ment and response to biotic and abiotic stress Proc

Natl Acad Sci USA 92, 4114–4119

32 Hause B, Demus U, Teichmann C, Parthier B &

Wasternack C (1996) Developmental and tissue-specific

expression of JIP-23, a jasmonate-inducible protein of

barley Plant Cell Physiol 37, 641–649

33 McConn M & Browse J (1996) The critical requirement

for linolenic acid is pollen development, not

photosyn-thesis, in an Arabidopsis mutant Plant Cell 8, 403–416

34 Ishiguro S, Kawai-Oda A, Ueda J, Nishida I & Okada

K (2001) The DEFECTIVE IN ANTHER

DEHI-SCIENCE1gene encodes a novel phospholipase A1

catalyzing the initial step of jasmonic acid biosynthesis,

which synchronizes pollen maturation, anther

dehis-cence, and flower opening in Arabidopsis Plant Cell 13,

2191–2209

35 Pauwels L, Inze´ D & Goossens A (2009)

Jasmonate-inducible gene: what does it mean? Trends Plant Sci 14,

87–91

36 Feys B, Benedetti CE, Penfold CN & Turner JG (1994)

Arabidopsismutants selected for resistance to the

phy-totoxin coronatine are male-sterile, insensitive to methyl

jasmonate, and resistant to a bacterial pathogen Plant

Cell 6, 751–759

37 Stintzi A & Browse J (2000) The Arabidopsis

male-ster-ile mutant, opr3, lacks the 12-oxophytodienoic acid

reductase required for jasmonate synthesis Proc Natl

Acad Sci USA 97, 10625–10630

38 Sanders PM, Lee PY, Biesgen C, Boone JD, Beals TP,

Weiler EW & Goldberg RB (2000) The arabidopsis

DELAYED DEHISCENCE1gene encodes an enzyme

in the jasmonic acid synthesis pathway Plant Cell 12,

1041–1061

39 Zhang Y & Turner JG (2008) Wound-induced

endoge-nous jasmonates stunt plant growth by inhibiting

mito-sis PLoS ONE 3, e3699

40 Blechert S, Brodschelm W, Ho¨lder S, Kammerer L,

Kutchan TM, Mueller MJ, Xia ZQ & Zenk MH (1995)

The octadecanoic pathway: signal molecules for the

regulation of secondary pathways Proc Natl Acad Sci

USA 92, 4099–4105

41 Weiler EW, Albrecht T, Groth B, Xia ZQ, Luxem M,

Liß H, Andert L & Spengler P (1993) Evidence for the

involvement of jasmonates and their octadecanoid

pre-cursors in the tendril coiling response of Bryonia dioica

Phytochemistry 32, 591–600

42 Stelmach BA, Mu¨ller A, Hennig P, Laudert D, Andert

L & Weiler EW (1998) Quantitation of the

octadeca-noid 12-oxo-phytodienoic acid, a signalling compound

in plant mechanotransduction Phytochemistry 47, 539–

546

43 Blechert S, Bockelmann C, Fu¨sslein M, Schrader T, Stelmach BA, Niesel U & Weiler EW (1999) Structure– activity analyses reveal the existence of two separate groups of active octadecanoids in elicitation of the ten-dril-coiling response of Bryonia dioica Jacq Planta 207, 470–479

44 Walter A, Mazars C, Maitrejean M, Hopke J, Ranjeva

R, Boland W & Mitho¨fer A (2007) Structural require-ments of jasmonates and synthetic analogues as induc-ers of Ca2+signals in the nucleus and the cytosol of plant cells Angew Chem Int Ed Engl 46, 4783–4785

45 Lecourieux D, Ranjeva R & Pugin A (2006) Calcium in plant defence-signalling pathways New Phytol 171, 249–269

46 Mazars C, Bourque S, Mithofer A, Pugin A & Ranjeva

R (2009) Calcium homeostasis in plant cell nuclei New Phytol 181, 261–274

47 Tretner C, Huth U & Hause B (2008) Mechanostimula-tion of Medicago truncatula leads to enhanced levels of jasmonic acid J Exp Bot 59, 2847–2856

48 Ueda M & Nakamura Y (2006) Metabolites involved

in plant movement and ‘memory’: nyctinasty of legumes and trap movement in the Venus flytrap Nat Prod Rep 23, 548–557

49 Ueda M & Nakamura Y (2007) Chemical basis of plant leaf movement Plant Cell Physiol 48, 900–907

50 Nakamura Y, Miyatake R & Ueda M (2008) Enantio-differential approach for the detection of the target membrane protein of the jasmonate glycoside that con-trols the leaf movement of Albizzia saman Angew Chem Int Ed Engl 47, 7289–7292

51 Riemann M, Mu¨ller A, Korte A, Furuya M, Weiler

EW & Nick P (2003) Impaired induction of the jasmo-nate pathway in the rice mutant hebiba Plant Physiol

133, 1820–1830

52 Gutjahr C, Riemann M, Mu¨ller A, Du¨chting P, Weiler

EW & Nick P (2005) Cholodny-Went revisited: a role for jasmonate in gravitropism of rice coleoptiles Planta

222, 575–585

53 Riemann M, Gutjahr C, Korte A, Riemann M, Danger

B, Muramatsu T, Bayer U, Waller F, Furuya M & Nick P (2007) GER1, a GDSL motif-encoding gene from rice is a novel early light- and jasmonate-induced gene Plant Biol (Stuttg) 9, 32–40

54 Riemann M, Bouyer D, Hisada A, Mu¨ller A, Yatou O, Weiler EW, Takano M, Furuya M & Nick P (2009) Phytochrome A requires jasmonate for photodestruc-tion Planta 229, 1035–1045

55 Danon A, Miersch O, Felix G, op den Camp RG & Apel K (2005) Concurrent activation of cell death-regu-lating signaling pathways by singlet oxygen in Arabid-opsis thaliana Plant J 41, 68–80

56 op den Camp RG, Przybyla D, Ochsenbein C, Laloi C, Kim C, Danon A, Wagner D, Hideg E, Go¨bel C, Feussner I et al (2003) Rapid induction of distinct