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The role of TAL effectors in virulence of Xanthomonas campestris pv. campestris

Zoe Dubrow: Cornell University

<div><em>Xanthomonas campestris</em> pv. <em>campestris</em> (<em>Xcc</em>), the causal agent of black rot of crucifers, is one of the most important <em>Brassica</em> pathogens worldwide. Transcription activator-like effectors (TALEs) are a large family of type III secreted effectors present in some <em>Xanthomonas</em> species that play a role in bacterial colonization of host plants. The first four Xcc genomes published showed no evidence of TALEs, suggesting <em>Xcc</em> lacked them. However, more recent work and reclassification of <em>Xanthomonas campestris</em> pathovars have shown that some <em>Xcc</em> strains do contain TALEs. We used PCR and western and Southern blotting to survey 124 <em>Xcc</em> isolates from a 10-year New York State collection and found 30% of the isolates have TALE genes and that the TALEs are expressed. The New York <em>Xcc</em> isolates have different TALE repertoires even among isolates found by MLSA to be closely related. To understand the role of TALEs in black rot of crucifers, we are sequencing the <em>Xcc </em>TALEs and determining by targeted mutagenesis whether they contribute to <em>Xcc</em> virulence. We will identify susceptibility (S) genes upregulated by important TALEs. These data could inform targeted resistance breeding approaches for cruciferous vegetables.</div>