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Front Plant Sci. 2019 Apr 30;10:507. doi: 10.3389/fpls.2019.00507. eCollection 2019.

A Pathovar of Xanthomonas oryzae Infecting Wild Grasses Provides Insight Into the Evolution of Pathogenicity in Rice Agroecosystems.

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Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, United States.
IRD, Cirad, Univ. Montpellier, IPME, Montpellier, France.
Centre Régional de Recherche Agronomique de Niono, Institut d'Economie Rural, Bamako, Mali.
Laboratoire de Biologie Moléculaire Appliquée, Université des Sciences Techniques et Technologiques de Bamako, Bamako, Mali.
Pacific Biosciences, Menlo Park, CA, United States.
Department of Plant Pathology, Infectious Disease Institute, Ohio State University, Columbus, OH, United States.
International Rice Research Institute, Los Baños, Philippines.


Xanthomonas oryzae (Xo) are globally important rice pathogens. Virulent lineages from Africa and Asia and less virulent strains from the United States have been well characterized. Xanthomonas campestris pv. leersiae (Xcl), first described in 1957, causes bacterial streak on the perennial grass, Leersia hexandra, and is a close relative of Xo. L. hexandra, a member of the Poaceae, is highly similar to rice phylogenetically, is globally ubiquitous around rice paddies, and is a reservoir of pathogenic Xo. We used long read, single molecule real time (SMRT) genome sequences of five strains of Xcl from Burkina Faso, China, Mali, and Uganda to determine the genetic relatedness of this organism with Xo. Novel transcription activator-like effectors (TALEs) were discovered in all five strains of Xcl. Predicted TALE target sequences were identified in the Leersia perrieri genome and compared to rice susceptibility gene homologs. Pathogenicity screening on L. hexandra and diverse rice cultivars confirmed that Xcl are able to colonize rice and produce weak but not progressive symptoms. Overall, based on average nucleotide identity (ANI), type III (T3) effector repertoires, and disease phenotype, we propose to rename Xcl to X. oryzae pv. leersiae (Xol) and use this parallel system to improve understanding of the evolution of bacterial pathogenicity in rice agroecosystems.


Xanthomonas oryzae; agroecosystem; cutgrass; rice; transcription activator-like effectors (TALEs)

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