Poster: Plant Pathogen/Symbiont Interactions

Abs # 702: The R genes RPP8 and RPH8A are induced by pathogen attack, BTH application, and wounding.

Presenter:	Mammarella, Nicole D., nicole@vt.edu
Authors	Mammarella, Nicole D. (A)   Woffenden, Bonnie J. (A)   Simon, Stacey A. (A)   Gilbert, Crystal  (A)   Jelesko, John G. (A)   McDowell, John M. (A)
Affiliations:	(A): Virginia Tech

Race-specific resistance leading to the hypersensitive response (HR) is activated by R genes, which are believed to encode proteins that detect invading pathogens. In certain cases, plants with only one copy of a functional R gene (e.g. heterozygotes) are more susceptible than homozygous plants. In contrast, overexpression of certain R genes can spontaneously activate defense responses, leading to costly physiological effects including HR-like cell death and reduced yield. Thus, proper regulation of R gene expression levels is crucial for efficient defense. We are using chimeric reporter genes and quantitative RT-PCR to explore the regulation of RPP8 (responsible for recognition of the Emco5 isolate of Peronospora parasitica) and the paralogous gene RPH8A (unknown function) in Arabidopsis. Both RPP8 and RPH8A are induced by challenge with Emco5, BTH (a synthetic analog of salicylic acid), and wounding. These results indicate that RPP8 and RPH8A are regulated by defense signaling feedback loops, perhaps to enhance defense responses by boosting R protein levels. Surprisingly, RPP8 and RPH8A are also induced by mechanical wounding, and are preferentially expressed in different tissues. Taken together, these results counter the assumption that R gene expression is static. Rather, R genes may be capable of dynamically responding to input from diverse environmental and developmental stimuli.