PEPR2 Is a Second Receptor for the Pep1 and Pep2 Peptides and Contributes to Defense Responses inArabidopsis 

Abstract

Pep1 is a 23-amino acid peptide that enhances resistance to a root pathogen, Pythium irregulare. Pep1 and its homologs (Pep2 to Pep7) are endogenous amplifiers of innate immunity of Arabidopsis thaliana that induce the transcription of defense-related genes and bind to PEPR1, a plasma membrane leucine-rich repeat (LRR) receptor kinase. Here, we identify a plasma membrane LRR receptor kinase, designated PEPR2, that has 76% amino acid similarity to PEPR1, and we characterize its role in the perception of Pep peptides and defense responses. Both PEPR1 and PEPR2 were transcriptionally induced by wounding, treatment with methyl jasmonate, Pep peptides, and pathogen-associated molecular patterns. The effects of Pep1 application on defense-related gene induction and enhancement of resistance to Pseudomonas syringae pv tomato DC3000 were partially reduced in single mutants of PEPR1 and PEPR2 and abolished completely in double mutants. Photoaffinity labeling and binding assays using transgenic tobacco (Nicotiana tabacum) cells expressing PEPR1 and PEPR2 clearly demonstrated that PEPR1 is a receptor for Pep1-6 and that PEPR2 is a receptor for Pep1 and Pep2. Our analysis demonstrates differential binding affinities of two receptors with a family of peptide ligands and the corresponding physiological effects of the specific receptor-ligand interactions. Therefore, we demonstrate that, through perception of Peps, PEPR1 and PEPR2 contribute to defense responses in Arabidopsis.

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

“…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.…”

“…PEPR1 and PEPR2 appear to have different preferences for AtPeps. For example, AtPep1-6 have a similar activity of inducing PEPR1-mediated plant immune responses, whereas PEPR2 is preferentially responsive to AtPep1-2 [20]. Ca 2+ has been shown to be important for the AtPep/ PEPR signaling [21,22].…”

“…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.…”

Functional importance of BAK1 tyrosine phosphorylation in vivo

“…29,30 In its role as coreceptor, BAK1 is thought to bind to the receptor kinase in a ligand-dependent manner, and to then autophosphorylate and also transphosphorylate sites on the receptor kinase. 2 How the various functions and interactions of BAK1 are regulated is not known but conceivably site-specific (auto) phosphorylation could play a role.…”