A single-amino acid substitution in the sixth leucine-rich repeat of barley MLA6 and MLA13 alleviates dependence on RAR1 for disease resistance signaling.
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.
Halterman
Dennis A
DA
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.
Wise
Roger P
RP
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
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