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SPECIAL SESSION: Pathogen Adaptation to the Plant Vascular System

Basis for Xanthomonas vascular plant pathogenesis
Jonathan Jacobs - Department of Plant Pathology, The Ohio State University.

Pathogenic microorganisms cause vascular and non-vascular diseases of animals and plants. The factors that contribute to pathogen evolution for niche-specific, vascular or non-vascular behavior remain unclear. We determined a single gene, celA, distinguishes vascular from non-vascular Gram-negative plant pathogens. Among all sequenced plant-associated microbes, cellobiosidase CelA was found in vascular pathogens from three distinct genera: Xanthomonas, Xylella, and Ralstonia. Phylogenomics revealed that celA was lost from apoplast-colonizing Xanthomonas pathogens suggesting vascular behavior predates non-vascular host colonization. Notably expression of CelA permitted pathotype conversion, where apoplast barley and rice Xanthomonas pathogens were able to cause vascular blight pathogenesis. We overall suspect that vascular pathogenesis was an ancient phytopathogenic behavior, and genes such as celA were lost upon switching niche-specificity.