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Molecular Characterization of Race 1 Bacterial Speck Resistance in a Wild Relative of Tomato

Carolina Mazo: School of Integrated Plant Science, Cornell University

<div><em>Pseudomonas syringae</em> pv. <em>tomato</em> (<em>Pst</em>) is a persistent pathogen of tomato that causes bacterial speck disease. On tomato, resistance conferred by the<em> R</em> gene <em>Pto</em> is effective against race 0 <em>Pst</em> strains which express the effector proteins AvrPto and/or AvrPtoB; however, race 1 strains of <em>Pst, </em>which do not express AvrPto/AvrPtoB but rather a different repertoire of effectors, evade <em>Pto</em>-mediated resistance. In this study, we aimed to characterize a putative <em>R</em> gene discovered in a wild relative of tomato that recognizes AvrRpt2, a bacterial effector widespread in race 1 <em>Pst</em> strains. In <em>Arabidopsis</em>, the <em>R</em> gene <em>RPS2</em> recognizes AvrRpt2. We found that certain mutations in AvrRpt2 that impair its recognition by RPS2 do not affect its recognition in tomato plants that harbor our putative <em>R</em> gene. This observation suggests there might be a novel AvrRpt2 recognition mechanism in this tomato accession. Additionally, by transiently expressing AvrRpt2 homologs from different bacterial phytopathogens we found that recognition of the effector by the putative <em>R </em>protein correlates with the reported ability of each homolog to cleave<em> Arabidopsis</em> RIN4, which is an indicative of AvrRpt2 cysteine protease activity. Together, these results provide a foundation for investigating molecular mechanisms underlying the interaction between AvrRpt2 and a new tomato R gene and may lead to the development of <em>Pst</em> race 1 resistant tomato varieties.</div>