Mimicry of The Plant Hormone PSY1 by A Sulfated Bacterial Peptide, RaxX
A. JOE (1), R. Pruitt (1) (1) Department of Plant pathology the Genome Center, University of California Davis, USA, U.S.A.

Tyrosine sulfation is a post-translational modification that is increasingly recognized as an important modulator of protein-protein interactions.  Plants and animals employ tyrosine-sulfated proteins, to regulate growth, development, immunity and other important biological processes. We have recently identified the elicitor of XA21 as a small sulfated protein, which we named RaxX. Xoo strains lacking RaxX are able to evade XA21-mediated immunity. Sulfated, but not nonsulfated, RaxX triggers the hallmarks of the plant immune response in an XA21-dependent manner. RaxX is present in most Xanthomonas species but shares no homology with microbial proteins of known function. We have recently noted a remarkable similarity between the sulfated, secreted Arabidopsis 18 amino acid peptide signaling factor PSY1, four predicted rice PSY1 orthologs and RaxX residues 40-55. In Arabidopsis, PSY1 is a signal factor that promotes cellular proliferation and suppresses the immune response to biotrophic pathogens. We hypothesize that RaxX evolved to mimic PSY in order to mediate suppression of host defense responses, facilitate infection, or enhance plant growth. Here we show that sulfated RaxX peptide promotes Arabidopsis and rice root growth in the same manner as PSY1. However, PSY peptides do not activate XA21-mediated immunity suggesting that XA21 and the PSY receptor differentially recognize RaxX and endogenous PSY peptides. We will also present the result that sulfated RaxX can suppress rice immune responses.

Abstract Number: C5-5, P9-334
Session Type: Concurrent