Submitted to: The Plant Cell
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/31/2010
Publication Date: 2/23/2010
Publication URL: www.plantcell.org/cgi/doi/10.1105/tpc.109.068874
Citation: Yamaguchi, Y., Huffaker, A., Bryan, A.C., Tax, F.E., Ryan, C.A. 2010. PEPR2 is a second receptor for the Pep1 and Pep2 peptides and contributes to defense responses in arabidopsis. The Plant Cell. 22:508-522. Interpretive Summary: A small peptide was shown previously to contribute to pathogen resistance in plants by acting as an internal signal to trigger defense responses. The peptide activates multiple pathways of defense simultaneously and stimulates expression of genes encoding antimicrobial proteins that fight off microorganisms attacking the plant. Plants that were engineered to express the peptide gene at higher levels were more resistant to a widespread and damaging pathogen, Pythium, which causes a root rot disease in almost every species of plant, including many economically important crops. Previously it was shown that the small peptide binds to and interacts with a specific receptor protein, much as a specific key turns inside the corresponding lock to unlock and open a door. However, it was not known whether this lock and key mechanism was essential to turning on pathogen defense responses. Scientists at Washington State University the University of Arizona and the Center for Medical, Agricultural and Veterinary Entomology, USDA-ARS have defined the indispensable role that the receptor and a second newly discovered receptor play together in translating the peptide signal into downstream activation of pathogen resistance. In addition to the first receptor, the second receptor is shown to specifically bind the peptide signal, and the genes encoding both receptors are shown to turn on when the plant is confronted by pathogen-related stimuli. Plants that were missing either one of the two receptors were less effective at recognizing the peptide signal and initiating defense responses such as expression of genes encoding antimicrobial proteins. Plants that were missing both receptors did not recognize the peptide or activate defense responses at all. Finally, this report demonstrates that the peptide signal and two receptors are able to work together to confer resistance to a very different pathogen from Pythium; plants preinoculated with the peptide signal were more resistant to Pseudomonas syringae, a bacterial pathogen that causes leaf speck diseases in crop plants such as tomato. In addition to contributing to a better understanding of the molecular mechanisms regulating plant defense, this report indicates that the peptide signal/receptor lock and key system described herein may be used to confer plant resistance to a variety of different diseases.
Technical Abstract: A 23-amino acid peptide, AtPep1, and its homologues are endogenous elicitors in Arabidopsis, inducing defense related genes. AtPep1 enhances resistance to a root pathogen, Pythium irregulare, through the salicylic acid, jasmonic acid, ethylene, and reactive oxygen species signaling pathways. AtPep peptides bind to AtPEPR1, a plasma membrane leucine-rich repeat receptor kinase. In the Arabidopsis genome, there is a gene encoding a receptor kinase with 76 % amino acid similarity to the entire AtPEPR1 sequence; designated AtPEPR2. Both AtPEPR1 and AtPEPR2 were transcriptionally induced by wounding, treatment with methyl jasmonate and AtPep peptides. The effects of AtPep1 application on defense gene induction and enhancement of resistance to Pseudomonas syringae pv tomato DC3000 were partially reduced in single mutants of AtPEPR1 and AtPEPR2, and abolished completely in double mutants. The binding between AtPep1 and AtPEPR2 was confirmed by photoaffinity labeling using transgenic tobacco cells expressing AtPEPR2. These results clearly demonstrated that AtPEPR2 is a receptor for AtPep1 in addition to AtPEPR1, and that AtPEPR1 and AtPEPR2 both contribute to AtPEP1 mediated defense responses.