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 J. 2004 Apr;38(2):215-26. doi: 10.1111/j.1365-313X.2004.02032.x.


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.

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Ascomycota / pathogenicity
  • Base Sequence
  • Carrier Proteins / genetics*
  • Cloning, Molecular
  • DNA, Plant / genetics
  • Evolution, Molecular
  • Genes, Plant
  • Hordeum / genetics*
  • Hordeum / microbiology
  • Hordeum / physiology
  • Intracellular Signaling Peptides and Proteins
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Phylogeny
  • Plant Diseases / genetics
  • Plant Diseases / microbiology
  • Plant Proteins / chemistry
  • Plant Proteins / genetics*
  • Plants, Genetically Modified
  • Protein Structure, Tertiary
  • Repetitive Sequences, Amino Acid
  • Sequence Homology, Amino Acid
  • Signal Transduction / genetics


  • Carrier Proteins
  • DNA, Plant
  • Intracellular Signaling Peptides and Proteins
  • MLA6 protein, Hordeum vulgare
  • Plant Proteins
  • Rar1 protein, Hordeum vulgare

Associated data

  • GENBANK/AY266442
  • GENBANK/AY266443
  • GENBANK/AY266444
  • GENBANK/AY266445