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POSTERS: Genetics of resistance

Identification of a New Class of Transcription Activation-Like Effector, pthXp1, Among Xanthomonas perforans Strains Collected in Alabama
Eric Newberry - Auburn University. Rishi Bhandari- Auburn University, Neha Potnis- Auburn University

Bacterial leaf spot of tomato, caused by X. perforans, is an endemic disease in the southeast United States and major limiting factor to the production of tomatoes worldwide. The emergence of novel X. perforans lineages with varying type 3 secreted effector repertoires has important implications in the sustainability of genetic resistance as an effective disease management tool. One such resistance, Bs4, is found in several tomato varieties and confers a hypersensitive response to Xanthomonas sp. with a cognate avirulence gene, either avrBs3 or avrBs4. In a recent survey of the X. perforans population responsible for bacterial leaf spot of tomato in Alabama, we identified the presence of a transcription activation-like (TAL) effector with homology to avrBs3. As the strains carrying this gene failed to induce a Bs4-mediated resistance in tomato cv. Bonny Best, we obtained the completed TAL-effector sequence using a Phusion PCR approach. The sequence differed from the avrBs3 and avrBs4 effectors commonly found in related Xanthomonas sp. in that it was composed of 15.5 tandem repeats of 34 aa in length, rather than 17.5 and displayed 90 to 92% aa identity. Analysis of the repeat variable di-residues showed that the gene shared several blocks of homology with avrBs4; however, could not be assigned to same class as any TAL effector for which sequence data was available. As the predicted binding-specificity and host recognition of the gene was distinct from previously described TAL effectors in bacterial-spot xanthomonads, we propose the name pthXp1.