The cell surface leucine-rich repeat receptor for At Pep1, an endogenous peptide elicitor in Arabidopsis , is functional in transgenic tobacco cells

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Abstract
At Pep1 is a 23-aa endogenous peptide elicitor from Arabidopsis leaves that signals the activation of components of the innate immune response against pathogens. Here, we report the isolation of an At Pep1 receptor from the surface of Arabidopsis suspension-cultured cells. An 125 I-labeled At Pep1 analog interacted with suspension-cultured Arabidopsis with a K d of 0.25 nM, and an 125 I-labeled azido-Cys- At Pep1 photoaffinity analog specifically labeled a membrane-associated protein of ≈170 kDa. The labeled protein was purified to homogeneity, and its tryptic peptides were identified as gene At1g73080, which encodes a leucine-rich repeat receptor kinase, here called PEPR1. Verification of the binding protein as the receptor for At Pep1 was established by demonstrating the loss of function of microsomal membranes of two SALK insertional mutants and by a gain in function of the alkalinization response to At Pep1 by tobacco suspension-cultured cells expressing the At1g73080 transgene. Synthetic homologs of At Pep1, deduced from the C termini of six known paralogs of PROPEP1 , were biologically active and were competitors of the interaction of an At Pep1 radiolabeled analog with the receptor. The data are consistent with a role for PEPR1 as the receptor for At Pep1 to amplify innate immunity in response to pathogen attacks.