title: A single-amino acid substitution in the sixth leucine-rich repeat of barley MLA6 and MLA13 alleviates dependence on RAR1 for disease resistance signaling.
abstract: Interactions between barley and the powdery mildew pathogen, Blumeria graminis f. sp. hordei, (Bgh) are determined by unique combinations of host resistance genes, designated Mildew-resistance locus (Ml), and cognate pathogen avirulence genes. These interactions occur both dependent and independent of Rar1 (required for Mla12 resistance) and Sgt1 (Suppressor of G-two allele of skp1), 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 sixth leucine-rich repeat (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, as mutation of this residue to a structurally similar, but uncharged, asparagine did not alter RAR1 dependence. These results demonstrate that a single-amino acid substitution in the sixth MLA LRR can alter host signaling but not resistance specificity to B. graminis.
authors.affiliation: Corn Insects and Crop Genetics Research, USDA-ARS, Department of Plant Pathology, and Center for Plant Responses to Environmental Stresses, Iowa State University, Ames, IA 50011-1020, USA.
authors.forename: Dennis A
authors.initials: DA
authors.lastname: Halterman
authors.forename: Roger P
authors.initials: RP
authors.lastname: Wise
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001203:Ascomycota / Q000472:pathogenicity; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D018744:DNA, Plant / Q000235:genetics; D019143:Evolution, Molecular; D017343:Genes, Plant; D001467:Hordeum / Q000235:genetics* / Q000382:microbiology / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010802:Phylogeny; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics*; D030821:Plants, Genetically Modified; D017434:Protein Structure, Tertiary; D020449:Repetitive Sequences, Amino Acid; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000235:genetics
chemical_list: D002352:Carrier Proteins; D018744:DNA, Plant; D047908:Intracellular Signaling Peptides and Proteins; C430705:MLA6 protein, Hordeum vulgare; D010940:Plant Proteins; C499582:Rar1 protein, Hordeum vulgare