Journal of Experimental Botany
doi:10.1093/jxb/erv180
Review PaPeR
Quo vadis, Pep? Plant elicitor peptides at the crossroads of immunity, stress and development
Sebastian Bartels * and Thomas Boller
Zürich-Bal Plant Science Center, University of Bal, Department of Environmental Sciences, Botany, Hebelstras 1, CH-4056 Bal, Switzerland
* To whom correspondence should be addresd. E-mail: bastian.bartels@unibas.ch
Received 16 February 2015; Revid 14 March 2015; Accepted 17 March 2015
Abstract
在平面直角坐标系中
The first line of inducible plant defence, pattern-triggered immunity (PTI), is activated by the recognition of exogenous as well as endogenous elicitors. Exogenous elicitors, also called microbe-associated molecular patterns, signal the prence of microbes. In contrast, endogenous elicitors em to be generated and recognized under more diver circumstances, making the evaluation of their biological relevance much more complex. Plant elicitor peptides (Peps) are one class of such endogenous elicitors, which contribute to immunity against attack by bacteria, fungi, as well as herbivores. Recent studies indicate that the Pep-triggered signalling pathways also operate during the respon to a more diver t of stress including starvation stress. In addition, in silico data point to an involvement in the regulation of plant development, and a study on Pep-mediated inhibition of root growth supports this indication. Importantly, Peps are neither limited to the model plant Arabidopsis nor to a specific plant family like the previously intensively studied systemin peptides. On the contrary, they are prent and active in angiosperms all across the phylogenetic tree, including many important crop plants. Here we summarize the progress made in rearch on Peps from their discovery in 2006 until now. We discuss the two main models which describe their likely function in plant immunity, highlight the studies supporting additional roles of Pep-triggered signalling and identify urgent rearch tasks to further uncover their biological relevance.
Key words: DAMP , danger, Pep, PEPR, plant elicitor peptide, PTI.
Plant immunity triggered by endogenous elicitors: Peps emerge as the new paradigms
Plant innate immunity is triggered by the perception of mol-ecules of diver chemical composition originating from organisms as disparate as bacteria, fungi and herbivores. The molecules are generally called elicitors since they have the capacity to elicit an immune respon. Depending on their origin they can be subdivided into MAMPs (microbe-associ-ated molecular patterns; also known as pathogen-associated molecular patterns; PAMPs), HAMPs (herbivore-associated molecular patterns) or V AMPs (virus-associated molecular patterns). Plants evolved the ability to perceive the patterns by using pattern recognition receptors (PRRs), which are transmembrane receptors of various class but all are induc-ing, nevertheless, an astonishingly similar collection of physi-ological respons. This t of defence-associated respons has been termed ‘PAMP-triggered immunity’ (Jones and Dangl, 2006) or, more fittingly, ‘pattern-triggered immunity’ (PTI) (Boller and Felix, 2009). It compris quick and tran-sient as well as long-lasting physiological reactions, including
© The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights rerved. For permissions, plea email: journals.
高中历史必修一知识点总结Abbreviations: BAK1, BRI1-ASSOCIATED KINASE 1; DAMP , damage-associated molecular pattern; ET, ethylene; GDU, GLUTAMINE DUMPER; HAMP , herbivore-associated molecular pattern; JA, jasmonic acid; LRR, leucine-rich repeat; MAMP , microbe-associated molecular pattern; MAPK, mitogen-activated protein kina; NO, nitric oxide; Pep, plant elicitor peptide; PEPR, Pep receptor; Pst, Pudomonas syringae pv tomato ; PTI, pattern-triggered immunity; SA, salicylic acid; VAMP , virus-associated molecular pattern.
Journal of Experimental Botany Advance Access published April 23, 2015 at University of Connecticut on July 6, 2015咱们是兄弟
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for example the production of reactive oxygen species, the induction of defence-related genes or the fortification of the cell wall.
In recent years it has become evident that endogenous pat-terns of the plant host also trigger PTI when perceived by the host itlf. The patterns have been assigned in the literature as damage- a
s well as danger-associated molecular patterns (DAMPs) (Boller and Felix, 2009). The parallel u of damage and danger in the context of DAMPs points already to mech-anistic as well as functional differences among DAMPs which starts with their formation. In brief, oligogalacturonides as well as cutin monomers are related to damage. They are pas-sively relead as a result of the activity of fungal enzymes try-ing to make way for the hyphae to enter the plant body (Boller and Felix, 2009; Ferrari et al., 2013). In contrast, the produc-tion and maybe also the relea of peptidic DAMPs like sys-temin or plant elicitor peptides (Peps) appear to be under tight control by the host (Ryan and Pearce, 2003; Yamaguchi and Huffaker, 2011). The former, especially oligogalacturonides, have been intensively studied and considerable progress has been made in understanding their generation, perception and subquent signalling events (Ferrari et al., 2013).
In ca of peptidic DAMPs, to date a number of plant peptides have been described which have the ability to trig-ger PTI-like defence respons (reviewed in Albert, 2013). For many years systemin was the paradigm for peptidic DAMPs but due to the controversy about its potential receptor and a limitation to family Solanaceae few recent systemin stud-ies have been published (Ryan and Pearce, 2003; Malinowski et al., 2009). In 2006 a family of plant elicitor peptides from Arabidopsis, called AtPeps, and their receptor PEPR1 (PEP-RECEPTOR1) were reported to activate components of PTI.
After identification of the cond receptor for AtPeps, called PEPR2, the Pep rearch intensified (Huffaker et al., 2006; Yamaguchi et al., 2006, 2010; Krol et al., 2010). One year later the first homologue of AtPeps in maize (Zea mays), ZmPep1, was characterized and in 2013 it became evident that there are veral active Pep homologues prent in diver plant species (Huffaker et al., 2011, 2013). In the meantime perception of Peps was shown to improve the resistance of Arabidopsis and maize plants against bacterial or fungal infections as well as feeding herbivores (Huffaker et al., 2011, 2013; Tintor et al., 2013; Klaur et al., 2015). The studies substantiated the initial hypothesis that Peps act as amplifiers of innate immu-nity. At the same time, an analysis of microarray data indi-cated that Peps might play an additional role in the respon to stress beside biotic stress and may even take part in the regulation of plant development (Bartels et al., 2013). In this regard two studies have recently prented the first experi-mental evidence. Ma et al. reported that Pep perception might inhibit root growth via regulation of GLUTAMINE DUMPER (GDUs) genes encoding amino acid exporters (Ma et al., 2014), and work from our lab uncovered an accel-eration of starvation-induced nescence upon Pep percep-tion (Gully et al., 2015). While Pep rearch has thus far been covered only by broader reviews highlighting advances in plant immunity or the role of signalling peptides in general (Yamaguchi and Huffaker, 2011; Albert, 2013; Ferrari et al., 2013), we dedicate this review exclusively to the Pep-PEPR system to give a comprehensive overview including Pep-PEPR specific features.
The molecular machinery: genesis of Peps
The first Pep to be described was AtPep1, a peptide isolated
from an extract of wounded Arabidopsis leaves, consisting of
the last 23 C-terminal amino acids of its precursor protein, called PROPEP1 (Huffaker et al., 2006). PROPEPs are small proteins of ~100 amino acids and are usually encoded by small gene families. Eight PROPEP genes have been identi-
fied in Arabidopsis and ven in maize, of which at least five show activity (Huffaker and Ryan, 2007; Bartels et al., 2013; Huffaker et al., 2013). Despite their low quence homol-
ogy even within the PROPEP gene family of one species, a large number of PROPEPs has been found in numerous spe-
cies within the angiosperms including important crop plants (Huffaker et al., 2013; Lori et al., 2015).
In terms of the transcriptional regulation of PROPEPs
in Arabidopsis and maize, there are two common principles. First, Pep perception triggers the transcription of at least the corresponding PROPEP in a positive feedback loop. Second,
most PROPEPs are induced by wounding and jasmonic acid (JA) (Huffaker and Ryan, 2007; Huffaker et al., 2011, 2013; Bartels et al., 2013; Ross et al., 2014). In contrast, challenge
with pathogens specifically induces individual PROPEPs. AtPROPEP1 and ZmPROPEP1 have been shown to respond
to infection with fungal pathogens whereas transcription of AtPROPEP3 and ZmPROPEP3 ris upon detection of her-bivores (Huffaker et al., 2011, 2013; Liu et al., 2013; Klaur
et al., 2015).
The PROPEP gene family of Arabidopsis has been most intensively characterized (e.g. in comparison to the PROPEP
gene family of maize) and displays best the complex regula-
tion of the individual PROPEPs within one family. Rearch
has focud here on the first three AtPROPEPs due to their apparent connections to plant immunity; thus, little is known about the regulation of AtPROPEP4 to AtPROPEP8. Regarding the latter, currently only wounding ems to induce the transcription of AtPROPEP5 and AtPROPEP8,
and this induction is restricted to the midrib of adult leaves, whereas AtPROPEP4 and AtPROPEP7 are not induced at
all (Bartels et al., 2013). Moreover, neither treatment with
JA, salicylic acid (SA) nor with AtPep1 to AtPep6 led to elevated transcription of AtPROPEP4, AtPROPEP5 and AtPROPEP6 (Huffaker and Ryan, 2007). Accordingly, a biclustering analysis bad on biotic stress-related microar-
站立的拼音
ray data did not show a clustering of the genes with genes related to defence but rather with genes involved in process
like terpenoid (gibberellin) biosynthesis, chromatin organiza-
tion and reproduction. Thus, despite a PTI-inducing activity
of AtPep4 to AtPep8, their precursors might be additionally involved in cellular process unrelated to defence (Bartels
et al., 2013).
In contrast, regulation of AtPROPEP1, AtPROPEP2 and AtPROPEP3 has been studied in more detail. The aforemen-tioned biclustering analysis showed a co-regulation of all
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three genes with genes linked to plant defence process, but only AtPROPEP2 and AtPROPEP3 appeared to be regu-lated similarly whereas AtPROPEP1 was found in a different cluster of genes (Bartels et al., 2013).
反跳性失眠
AtPROPEP1 transcription in leaves was shown to be induced by danger-related treatments like bacterial elicitors, wounding, fungal infection, methyl jasmonate, ethephon (which releas ethylene), and some AtPeps but not by methyl salicylate (Huffaker et al., 2006; Huffaker and Ryan, 2007; Yamaguchi et al., 2010; Bartels et al., 2013; Liu et al., 2013). Induction of AtPROPEP1 transcription by AtPep1 was impaired in the ethylene signalling mutant ein2-1 and the JA synthesis triple mutant fad3,7,8, as well as by co-appli-cation of diphenyleneiodonium chloride, an inhibitor of the NADPH oxidas involved in the formation of reactive oxy-gen species (Huffaker et al., 2006).
Microarray data and other recent studies have shown that the transcription of AtPROPEP2 and AtPROPEP3 is induced upon treatment with AtPeps, bacterial elicitors, as well as fungal and bacterial pathogens (Huffaker et al., 2006; Huffaker and Ryan, 2007; Tintor et al., 2013; Ross et al., 2014). Transcription of both genes is also induced upon wounding but, like the transcription of AtPROPEP1, induc-tion is restricted to the midrib of the leaf (Bartels et al., 2013). Interestingly, treatment with Spodoptera littoralis oral cre-tions or continuous darkness only induced the transcription of AtPROPEP3 and not AtPROPEP1 (Gully et al., 2015; Klaur et al., 2015). Similarly, induction of AtPROPEP2 transcription by elf18 (the active epitope of bacterial elon-gation factor Tu; EF-Tu) perception was impaired in ein2 mutants whereas AtPROPEP3 transcription was independ-e
nt of functional ethylene signalling (Tintor et al., 2013). Notably, in their follow-up study the authors showed that elevated transcription of both genes bad on treatments with Pudomonas syringae pv tomato (Pst ) ∆hrpS and Pst avrRpm1 was not impaired by mutations in ein2 as well as dde2 or sid2, affecting ET, JA and SA signalling, respectively.
The authors concluded that induction of both genes is espe-cially robust to perturbations in defence hormone pathways (Ross et al., 2014).
The promoters of AtPROPEP2 and AtPROPEP3 have been analyd in more detail than other PROPEP promot-ers. They share W boxes, cis-regulatory modules bound by WRKY transcription factors. Accordingly, the authors found in vivo association of WRK Y33 with both promoters, and induction of AtPROPEP2 and AtPROPEP3 transcription by treatment with flg22 (the active epitope of bacterial flagellin) treatment was reduced in wrky33 mutant plants (Logemann et al., 2013).
Comparably little is known about AtPROPEP expres-sion in the different plant tissues. Analysis of trans-genic Arabidopsis promoter::GUS lines indicated that all AtPROPEPs are expresd in the root, although AtPROPEP4 and AtPROPEP7 are restricted to the root tips of primary and lateral roots. In leaves only the promoter activity of AtPROPEP5 was found to be relatively strong, whereas
the promoter of AtPROPEP3 led to weak staining and the oth-ers did not produce any detectable GUS staining. Similarly, in addition to AtPROPEP8, AtPROPEP3 and AtPROPEP5 are expresd in flowers (Bartels et al., 2013). To highlight the complexity of the transcriptional data, the current knowl-edge is summarized in Table 1.
As mentioned previously, PROPEPs are believed to be only the precursors of the active Peps since AtPep1 and AtPep5 have been isolated from Arabidopsis leaf extracts as PTI-inducing peptides and not the respective AtPROPEPs (Huffaker et al., 2006; Yamaguchi and Huffaker, 2011). Thus PROPEPs are suppod to be cleaved or somehow procesd to relea their Peps. Currently, very little is known about processing or cleav-age of signalling peptide precursors in plants (Tabata and Sawa, 2014). Systemin has been shown to be cleaved by treat-ment with intercellular wash fluid from tomato leaves or cell culture medium from tomato cell cultures but the responsible enzyme has not been determined (Dombrowski et al., 1999).
Table 1.
The transcriptional landscape of the Arabidopsis PEPR and PROPEP genes
Tissue
Treatments
Refs
Green reprents detected promoter activity (Tissue) or induction (Treatments) whereas red marks tissues without detectable promoter activity or lack of induction after the indicated treatment.
Abbreviations: nd, not determined; OS, oral cretions of Spodoptera littoralis ; Pst, Pudomonas syringae pv. tomato; Bc, Botrytis cinerea ; Pi, Phytophthora infestans .
References: 1, Huffaker et al., 2006; 2, Huffaker et al., 2007; 3, Yamaguchi et al., 2010; 4, Bartels et al., 2013; 5, Logemann et al., 2013; 6, Tintor et al., 2013; 7, Ross et al., 2014; 8, Gully et al., 2015.
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Similarly, Ni and Clark (2006), by treatment with a cauliflower extract, obrved the processing of recombinantly produced CLA V ATA3 protein, the precursor for CLA V ATA3 peptide that interacts with the CLA V ATA1/CLA V ATA2 receptor complex to regulate the stem cell number in the shoot apical meristem, but again no processing enzyme was identified. Only recently Arabidopsis type-II metacaspa METACASPASE-9 was identified to cleave the extracellular protein GRIM REAPER into the GRIM REAPER peptide that triggers cell death via binding to the extracellular domain of POLLEN‐SPECIFIC RECEPTOR‐LIK E K INASE 5 (PRK5) (Wrzaczek et al., 2015). Since METACASPASE-9 as well as other plant meta-caspas are lysine and arginine-specific proteas (Vercammen et al., 2006; Tsiatsiani et al., 2011) and AtPROPEP1 contains an arginine in front of the AtPep1 quence, which appears to be conrved, it will be intriguing to investigate if metacaspas might process PROPEPs. If METACASPASE-9 would be the processing enzyme an export or relea of PROPEPs into the apoplast prior to cleavage would be required. Currently PROPEPs have only been shown to localize to the cytosol with or without association with the tonoplast; thus intracellular metacaspas might be more likely targets for PROPEP pro-cessing (Tsiatsiani et al., 20
11; Bartels et al., 2013).
Similar to METACASPASE-9 the extracellular aspartic protea CDR1 has been propod to be a good candidate for PROPEP cleavage since CDR1 is assumed to create a mobile peptidic PTI-inducing signal which might compri one or veral Peps (Xia et al., 2004; Vlot et al., 2008). But also in this ca, PROPEPs would first need to enter the apoplastic space. The prence of AtPep1 and AtPep5 in the leaf protein extract might also have been an artefact of protein extrac-tion and as a conquence uncleaved PROPEPs could be the active compounds in planta. The structurally and function-ally cloly related systemin peptide from tomato (Solanum lycopersicum) does not need cleavage. It has been shown that its precursor, prosystemin, is as active as the systemin peptide (Dombrowski et al., 1999).
Cleavage of precursors to relea active signalling peptides is a common principle in plant and animal defence and devel-opment (Khimji and Rockey, 2010; Goyette and Geczy, 2011; van de Veerdonk et al., 2011; Albert, 2013; Czyzewicz et al., 2013). In animals examples for both exist. Prointerleukin-1α, the precursor of interleukin-1α (IL-1α), was similarly active in inducing IL-6 relea compared to its mature form IL-1α. In contrast, the proIL-1β was inactive. ProIL-1β needs to be by caspa-1 into the active form IL-1β (Kim et al., 2013).
Taken together, PROPEPs might or might not be cleaved to be active. Detection and localization of cleavage products in vivo together with the identification of processing enzymes is one of the most important rearch tasks at the moment, since it will help to uncover the circumstances of Pep relea and perception.
Perception of Peps by PEPRs
PEPRs, the receptors for Peps (and maybe PROPEPs), are transmembrane receptors belonging to the large class of leucine-rich repeat (LRR) receptor-like kinas (RLK s) (Yamaguchi et al., 2010). In Arabidopsis promoter::GUS analysis showed that both AtPEPR genes are constitutively expresd, mainly in the root (except for the root tip), but also
in the leaf veins and the stem (Table 1). Despite a restriction
of AtPEPR2 transcription to the stele of the root both show a
great overlap in their tissue expression pattern (Bartels et al., 2013; Ma et al., 2014). Transcriptional regulation is similarly uniform. Wounding as well as treatment with methyl jas-monate led to a rapid (30 min to 1 h) but transient induction
of AtPEPR1 and AtPEPR2 transcription (Yamaguchi et al., 2010). Moreover, feeding of a range of herbivores triggered a strong induction of both promoters (Klaur et al., 2015). But
there are also slight differences between the transcriptional regulation of both AtPEPRs. AtPEPR1 transcript levels
ri after treatment with AtPep1 to AtPep6 and the bacterial elicitor derived peptides flg22 and elf18 whereas AtPEPR2 transcription was significantly induced only by perception of AtPep1, AtPep2, AtPep4 and elf18 (Yamaguchi et al., 2010).
In summary, both AtPEPRs are transcribed in most plant organs, and they are induced by treatments linked to plant defence. Thus, they show a similar behaviour to the defence-related AtPROPEPs, but intriguingly, they do not overlap
with the transcription and regulation of AtPROPEP4 and AtPROPEP7.
Peps are detected by binding to the extracellular LRR-domain of a PEPR. In Arabidopsis, AtPEPR1 is able to detect
all eight AtPeps, whereas AtPEPR2 detects only AtPep1 and AtPep2 (Bartels et al., 2013). Recently,
the crystal structure
of the AtPEPR1-LRR domain in complex with AtPep1 was solved, revealing that especially the C-terminal ten residues
of AtPep1 interact intensively with the AtPEPR1-LRR (Tang
et al., 2015). Previously an alanine-substitution approach led
to the identification of three crucial and conrved amino acids within the C-terminal ten amino acids. Substitution of either rine15 or glycine17 to alanine or deletion of the terminal asparagine23 resulted in a dramatically decread nsitivity of
cell cultures to the modified AtPep1 peptides (Pearce et al., 2008). The importance of the amino acids was confirmed by
the AtPep1/AtPEPR1-LRR crystal structure but additional amino acids also contribute to a stable Pep-PEPR interaction. Moreover, interaction of AtPEPR1 with the co-receptor BAK1 (BRI1-ASSOCIATED KINASE1) was reported to be crucial
for mounting full strength defence respons upon AtPep1 per-ception (Roux et al., 2011). Modelling of the AtPEPR1-LRR/ AtPep1/AtBAK1-LRR complex revealed that proline19 as well
as glutamine21 and histidine22 em to support the AtPEPR1 AtBAK1 interaction (Tang et al., 2015).
However, a study on the interspecies compatibility of Peps
and PEPRs suggested a high plasticity of Pep and PEPR-LRR quences with impact on the Pep/PEPR-LRR interaction efficiency (Lori et al., 2015). Generally, Peps from one plant species are not perceived by plants from distantly related fam-ilies. For example AtPep1 is not recognized by maize plants
and likewi ZmPep1 is not detected by Arabidopsis. A clor
look at the amino acid quence of the Peps revealed sub-stantial differences and indicated that there is no common
and strictly conrved Pep-motif like the aforementioned
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r15, gly17 and asp23, but each plant family evolved its own rather distinct Pep-motif. This hypothesis was supported by a demonstration that Peps from distantly related plant species were recognized if the family-specific motif was introduced into the Pep amino acid quence (Lori et al., 2015).
Data mining within the growing number of quenced plant genomes revealed that homologues of AtPEPRs are prent in a large number of species throughout the angiosperms. Similar to the situation in Arabidopsis, most plant species con-tain either one or two PEPRs but very few of the have been characterized yet. Beside the two AtPEPRs from Arabidopsis ZmPEPR1 and SlPEPR1 were recently cloned, and their abil-ity to perceive ZmPep1 as well as SlPep1 and subquently activate PTI was shown by transient expression in Nicotiana benthamiana (Lori et al., 2015). Bad on the innsitivity of the Arabidopsis pepr1 pepr2 double mutant to all AtPeps in all usual bioassays (Krol et al., 2010; Yamaguchi et al., 2010; Flury et al., 2013), we can assume with confidence that th
e are the only receptors able to perceive Peps. Interestingly, comparison of the conrvation of the LRR and the kina domain of diver PEPRs has revealed that the LRRs have a much lower level of conrvation compared to the kina domains (Lori et al., 2015). This is another indication for a rapid evolution of the Pep-PEPR interaction, whereas the downstream sig-nalling pathways starting from the kina domain are highly conrved. In line with this idea is the obrvation that PEPRs can be transferred between plant families and still operate defence signalling pathways (Lori et al., 2015). This behaviour has been noted before for the EF-Tu receptor (EFR), which is prent only in Brassicaceae and triggers PTI upon detec-tion of the bacterial protein EF-Tu. EFR was successfully transferred into plants from the Solanaceae where it improved plant resistance against bacterial pathogens (Lacombe et al., 2010). Since both receptors share BAK1 as their co-receptor, it ems that BAK1-dependent defence signalling pathways are strictly conrved (Lacombe et al., 2010; Schulze et al., 2010; Roux et al., 2011).
PEPR-triggered downstream events
The molecular events following PEPR activation have been rather well studied and are summarized in Fig. 1. Apparently PEPRs operate signalling pathways that are in part similar or even identical to the ones activated by the receptors EFR and FLS2 (FLAGELLIN SENSING2) that detect the bac-teri
al MAMPs EF-Tu or flg22, respectively. Thus, next we chronologically list the events and highlight the similarities between Pep- and mainly flg22-triggered respons as well as the specialities of the former.
Receptor complex dynamics and
phosphorylation events
Similar to FLS2, upon ligand binding AtPEPRs interact with their co-receptor BAK1 followed by the phosphorylation of both BAK1 and AtPEPRs (Schulze et al., 2010). As previ-ously mentioned this interaction is likely to be stabilized by binding of the Pep peptide (Tang et al., 2015). BOTR YTIS-INDUCED K INASE 1 (BIK1) and its clost homologue
PBS1-LIKE 1 (PBL1) constitutively interact with AtPEPR1
and likely AtPEPR2 (Liu et al., 2013). BIK1 also gets phos-phorylated at least by AtPEPR1 upon Pep perception, and might subquently leave the complex in a similar fashion to
how it leaves the FLS2 receptor complex upon flg22 percep-
tion (Zhang et al., 2010). Lack of BIK1 and PBL1 compro-
mis Pep-induced respons (Liu et al., 2013; Ranf et al., 2014).
Production of cyclic GMP
In contrast to FLS2, AtPEPR1 and maybe also AtPEPR2 contain a cytosolic guanylyl cycla (GC) domain capable
of producing cyclic GMP (cGMP) (Kwezi et al., 2007; Qi
et al., 2010; Ma et al., 2012). Although cGMP levels pro-duced by recombinant AtPEPR1 in vitro are extraordinarily
low compared to GCs from animals (Ashton, 2011), it has nevertheless been propod that the GC activity of AtPEPR1
may form locally enough cGMP to activate the plasma mem-
brane located CYCLIC NUCLEOTIDE GATED CATION CHANNEL 2 (CNGC2) to promote influx of extracellular
Ca2+ and subquent Ca2+-dependent signalling (Qi et al., 2010; Ma et al., 2012).
情人节的礼物
Ca2+-influx and signalling
Like flg22, AtPep perception leads to a rapid elevation of cyto-
solic Ca2+ levels, which is partially dependent on functional
BIK1 and PBL1 (Krol et al., 2010; Ranf et al., 2011, 2014;
Flury et al., 2013). Increa of Ca2+ levels upon AtPep treat-
ment (but not flg22) is also significantly reduced in the defence
no death mutant (dnd1), which lacks a functional CNGC2 coding quence (Qi et al., 2010; Ma et al., 2012). Thus it has
been propod that Pep-triggered signalling involves extracel-
lular Ca2+ whereas flg22 signalling rather triggers the relea
of Ca2+ from intracellular Ca2+-stores (Ma et al., 2012). Ca2+-dependent signalling triggered upon AtPep1 or flg22 treat-
ment requires functional CA2+-DEPENDENT PROTEIN KINASES (CDPKs) since the cpk5 cpk6 cpk11 triple mutant showed reduced ROS production, defence gene expression as
well as lowered nsitivity to AtPep- or flg22-triggered resist-
ance against infection with the virulent pathogen Pst DC3000 (Boudsocq et al., 2010; Ma et al., 2013).
Production of nitric oxide (NO) and ROS
Addition of flg22 and AtPep to leaf tissue triggers the pro-duction of NO as well as ROS (Krol et al., 2010; Flury et al., 2013; Ma et al., 2013). Both are involved in many signalling pathways including pathogen defence signalling (Moreau
et al., 2010; Baxter et al., 2013). Block of NO as well as ROS signalling due to the addition of specific inhibitors impairs
Pep-triggered induction of defence gene expression (Huffaker
et al., 2006; Ma et al., 2013). Whereas AtPep-triggered NO production appears to be only slightly lower compared to
flg22-triggered NO, AtPep-application leads to only minor
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