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Poster: Molecular & Cellular Plant-Microbe Interactions: MPMI


Two complete genome sequences of a new pathovar of Xanthomonas oryzae infecting wild grasses provide insight into evolution of pathogenicity
J. LANG (1), R. Koebnik (2), A. Pérez-Quintero (2), E. DuCharme (1), B. Szurek (2), J. Leach (1), V. Verdier (2) (1) Colorado State University, U.S.A.; (2) Institut de recherche pour le développement (IRD), France

Xanthomonas oryzae (Xo) is a group of plant pathogenic bacteria composed of weak and highly virulent members that are genetically distinct from one another. Strains belonging to different virulent lineages from Africa and Asia and less virulent strains from the US have been used for comparative studies of pathogenicity and establishing effector repertoires. A close relative of Xo, X. campestris pv. leersiae (Xcl) was first described in 1957, and causes bacterial streak on the perennial grass, Leersia hexandra. L. hexandra is closely related to rice, globally ubiquitous around rice paddies, and is a reservoir of pathogenic Xo. We used draft and long read, single molecule, real time (SMRT) genome sequences of two strains of Xcl from China and Burkina Faso to determine the genetic relatedness of this organism with Xo. Novel transcription activator like (TAL) effectors and repeat variable domains (RVD) were discovered. Predicted TAL effector target sequences were identified in the available L. perrieri genome. Rice susceptibility gene homologs and unique TAL effector targets were also uncovered. Pathogenicity screening on L. hexandra and diverse rice cultivars confirmed that Xcl can colonize rice and produces weak not progressive symptoms. Overall, based on average nucleotide identity, effector repertoires and phenotype, we propose to rename Xcl to X. oryzae pv. leersiae and use this parallel system to better understand the evolution of pathogenicity in grasses.