Poster: Plant Pathogen/Symbiont Interactions

Abs # 772: A single amino acid substitution in the sixth leucine-rich repeat of barley MLA alleviates dependence on RAR1 for disease resistance signaling

Presenter:	Halterman, Dennis , dhalterm@iastate.edu
Authors	Halterman, Dennis  (A) (B)  Wise, Roger  (A) (B)
Affiliations:	(A): USDA-ARS Corn Insects and Crop Genetics Research Unit, Ames, IA 50011 (B): Department of Plant Pathology, Iowa State University, Ames, IA 50011

Interactions between barley and the powdery mildew pathogen, Blumeria graminis f. sp. hordei are determined by unique combinations of host resistance loci, designated Ml, and cognate pathogen avirulence genes. These interactions occur both dependent and independent of the downstream signaling genes Rar1 and Sgt1, which are differentially required for diverse resistance pathways. In order to utilize the intrinsic diversity between Mla alleles, we used phylogenetic analysis of predicted Mla-encoded proteins, including the newly isolated MLA7 and MLA10, to identify amino acids important in conferring RAR1-independent resistance. Our analysis indicates that the sixth LRR contains an exclusively conserved aspartate in the RAR1-independent MLA1 and MLA7, as opposed to a glycine at the same position in the RAR1-dependent MLA6, MLA10, MLA12, and MLA13. Site-directed mutagenesis of the glycine to aspartate in the MLA6 ORF enables Mla6-mediated resistance to be conferred in a Rar1-independent manner. These results indicate that downstream resistance signaling can be altered through a single amino change on the predicted a-helical surface of the LRR domain, in contrast to residues in the b-sheets hypothesized to determine resistance specificity on the concave side.