Submitted to: Plant and Animal Genome Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 10, 2004
Publication Date: January 10, 2004
Citation: Halterman, D.A., Wise, R.P. 2004. A single amino acid substitution in the sixth leucine-rich repeat of barley Mla6 and Mla13 alleviates dependence on Rar1 for disease resistance signaling. Plant and Animal Genome Conference Proceedings. XII Conference. p. 858. Technical Abstract: Interactions between barley and the powdery mildew pathogen, Blumeria graminis f. sp. hordei, are determined by unique combinations of host resistance genes, 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 plant disease-resistance pathways. We have isolated two new functional Mla alleles, Rar1-independent Mla7 and Rar1-dependent Mla10, as well as the Mla paralogs, Mla6-2 and Mla13-2. Utilizing the inherent diversity amongst Mla encoded proteins, we identified the only two amino acids exclusively conserved in RAR1-dependent Mla6, Mla10, Mla12, and Mla13 that differ at the corresponding position in RAR1-independent MLA1 and MLA7. Two- and three-dimensional modeling places these residues on a predicted surface of the 6th LRR domain at positions distinct from those within the beta-sheets hypothesized to determine resistance specificity. Site-directed mutagenesis of these residues indicates that RAR1 independence requires the presence of an aspartate at position 721, since mutation of this residue to a structurally similar, but uncharged, asparagine did not alter RAR1 signaling. These results demonstrate that a single amino acid substitution in the 6th MLA LRR can alter host signaling but not resistance-specificity to Blumeria graminis.