Poster: Plant Pathogen/Symbiont Interactions

Abs # 757: Characterization of Xa21-mediated developmental disease resistance

Presenter:	Bertolet, Bonnie S.
Authors	Bertolet, Bonnie S. (A)   Yoshikawa, Masa  (A)   Fanter, Rob K. (A)   Bishop, Anna M. (A)   Whalen, Maureen C. (A)
Affiliations:	(A): San Francisco State University

Disease resistance to Xanthomonas oryzae pv. oryzae (Xoo) mediated by the resistance gene Xa21 is developmentally controlled in rice. We examined the relationship between expression of four PR genes (OsPR1a, OsPR1b, OsPR1c, and OsOR10a) and Xa21-mediated developmental disease resistance. OsPR1b was highly induced in the incompatible interaction at 3-4 day post-inoculation. The timing of induction correlates with resistance. OsPR1c was cloned and characterized. Although OsPR1c sequence is highly similar to both OsPR1a and OsPR1b, its expression did not correlate with resistance. Expression of these four PR genes is typically higher in adult than in the juvenile stage and was generally higher in the incompatible interaction than in the compatible. Expression of these genes in response to Xoo is transient, rather than continuous. In general, expression was induced to a greater extent in mock-inoculated leaves than in compatible interactions. Mock-inoculation induced gene expression was similar to that in the incompatible interaction, indicating that these PR genes are wound responsive. Interestingly, this high level of gene expression was suppressed in an compatible interaction. This result suggests that the virulent strain may have activities that suppress host defense systems. We also examined other aspects of developmentally controlled resistance. Xa21 does not have an organ-specific expression pattern, however, the level of expression varies from organ to organ. Our progress toward identifying proteins that are differentially expressed during the developmental transition from susceptibility to resistance and identifying anatomical and morphological phase change characteristics will be presented.