Perception of the Arabidopsis Danger Signal Peptide 1 Involves the Pattern Recognition Receptor AtPEPR1 and Its Close Homologue AtPEPR2

Abstract

Plasma membrane-borne pattern recognition receptors, which recognize microbe-associated molecular patterns and endogenous damage-associated molecular patterns, provide the first line of defense in innate immunity. In plants, leucine-rich repeat receptor kinases fulfill this role, as exemplified by FLS2 and EFR, the receptors for the microbe-associated molecular patterns flagellin and elongation factor Tu. Here we examined the perception of the damage-associated molecular pattern peptide 1 (AtPep1), an endogenous peptide of Arabidopsis identified earlier and shown to be perceived by the leucine-rich repeat protein kinase PEPR1. Using seedling growth inhibition, elicitation of an oxidative burst and induction of ethylene biosynthesis, we show that wild type plants and the pepr1 and pepr2 mutants, affected in PEPR1 and in its homologue PEPR2, are sensitive to AtPep1, but that the double mutant pepr1/pepr2 is completely insensitive. As a central body of our study, we provide electrophysiological evidence that at the level of the plasma membrane, AtPep1 triggers a receptor-dependent transient depolarization through activation of plasma membrane anion channels, and that this effect is absent in the double mutant pepr1/pepr2. The double mutant also fails to respond to AtPep2 and AtPep3, two distant homologues of AtPep1 on the basis of homology screening, implying that the PEPR1 and PEPR2 are responsible for their perception too. Our findings provide a basic framework to study the biological role of AtPep1-related danger signals and their cognate receptors.In plant immunity, a first line of defense is based on the perception of a group of conserved, pathogen-derived molecules, called microbe-associated molecular patterns (MAMPs) 4 by pattern recognition receptors, which cause the expression of defense genes as well as metabolic rearrangements, and ultimately activate basal resistance to potential pathogens (1, 2). In Arabidopsis, the best studied MAMPs are the bacterial flagellin (active epitope flg22) and elongation factor Tu (active EF-Tu epitopes elf13, elf18, and elf26), which are recognized by their cognate leucine rich repeat-receptor-like kinases FLS2 (flagellin-sensitive 2) and EFR (EF-Tu receptor), respectively (reviewed in Ref. 1). Perception of these MAMPs leads to a set of responses that can be used to monitor the recognition process, including the triggering of ion fluxes, the generation of reactive oxygen species (ROS), accumulation of ethylene, and finally up-regulation of defense-related genes; investment into increased resistance against bacterial pathogens negatively feeds back on plant growth (3). In addition to these MAMP/ pattern recognition receptor systems, another class of surveillance system recognizes plant-derived molecules previously known as "endogenous elicitors" and now as DAMPs (damageassociated molecular patterns): DAMPs are endogenous molecules that newly appear in the intercellular space in response to the damage caused by a pathogen attack, e.g. cell wall fragments or effectors deri...

Structural basis for recognition of an endogenous peptide by the plant receptor kinase PEPR1

“…It is noteworthy to point out that, while only AtPep1,2 induced medium alkalinization in PEPR2-expressing tobacco cells [20], AtPep1,2,3 were equally active in eliciting membrane depolarization of pepr1 mutants of Arabidopsis [19]. Our structural and biochemical data suggest that the C-terminal extensions in AtPep2,4,5 interfere with the assembly of the PEPR1-BAK1 complex.…”

“…While much less dense as compared to AtPep1-PEPR1LRR contacts mediated by the C-terminal portion of AtPep1, these non-conserved interactions are likely also important for AtPep1-induced signaling as AtPep1(14-23) is nearly inactive in inducing cell immune responses when tested at lower concentrations [15]. However, a higher concentration (25 nM) of the peptide, but not AtPep1 (15)(16)(17)(18)(19)(20)(21)(22)(23), displayed immunogenic activity, though lower than that of the wild-type peptide [15]. These results suggest that AtPep1 (14)(15) linking the conserved C-terminal and non-conserved N-terminal regions of AtPep1 may function as a hot spot for AtPep1-PEPR1LRR interaction.…”

“…A later study using alanine-scanning analysis showed that an AtPep1-derived peptide with the N-terminal deletion of eight amino acids, AtPep1 (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23), is equally active as the wild-type peptide in inducing PTI-like responses [15]. AtPep1 and its homologs AtPep2-8 mature from the conserved C-terminal portion of their respective precursors PROPEP1-8, respectively [14,16].…”

“…While displaying different expression patterns and localizations, all the eight AtPeps have a similar function of inducing plant immunity [16]. PEPR1 and its homolog PEPR2 are RKs with extracellular leucine-rich repeat (LRR) motifs (also found in FLS2 and EFR) and npg www.cell-research.com | Cell Research function as receptors of AtPeps [18][19][20], although in vitro reconstitution of these complexes is not available yet. PEPR1 and PEPR2 appear to have different preferences for AtPeps.…”

Role of autophagy in disease resistance and hypersensitive response-associated cell death

“…24,25 Such accumulated cellular debris may well disrupt homeostasis, leading to pleiotropic effects including accumulation of danger-associated molecular patterns (DAMPs) 68 triggering SA accumulation, and subsequent production of secreted pathogenesis-related (PR) proteins accompanied by ER stress. Autophagy is required to dampen the deleterious effects caused by ER stress and it is well described in other models that atg mutants die upon increased ER stress.…”