Cytosolic activation of cell death and stem rust resistance by cereal MLA-family CC-NLR proteins

Proc Natl Acad Sci U S A. 2016 Sep 6;113(36):10204-9. doi: 10.1073/pnas.1605483113. Epub 2016 Aug 23.

Abstract

Plants possess intracellular immune receptors designated "nucleotide-binding domain and leucine-rich repeat" (NLR) proteins that translate pathogen-specific recognition into disease-resistance signaling. The wheat immune receptors Sr33 and Sr50 belong to the class of coiled-coil (CC) NLRs. They confer resistance against a broad spectrum of field isolates of Puccinia graminis f. sp. tritici, including the Ug99 lineage, and are homologs of the barley powdery mildew-resistance protein MLA10. Here, we show that, similarly to MLA10, the Sr33 and Sr50 CC domains are sufficient to induce cell death in Nicotiana benthamiana Autoactive CC domains and full-length Sr33 and Sr50 proteins self-associate in planta In contrast, truncated CC domains equivalent in size to an MLA10 fragment for which a crystal structure was previously determined fail to induce cell death and do not self-associate. Mutations in the truncated region also abolish self-association and cell-death signaling. Analysis of Sr33 and Sr50 CC domains fused to YFP and either nuclear localization or nuclear export signals in N benthamiana showed that cell-death induction occurs in the cytosol. In stable transgenic wheat plants, full-length Sr33 proteins targeted to the cytosol provided rust resistance, whereas nuclear-targeted Sr33 was not functional. These data are consistent with CC-mediated induction of both cell-death signaling and stem rust resistance in the cytosolic compartment, whereas previous research had suggested that MLA10-mediated cell-death and disease resistance signaling occur independently, in the cytosol and nucleus, respectively.

Keywords: cell death; plant immunity; resistance protein; signaling; wheat stem rust.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Basidiomycota / pathogenicity
  • Basidiomycota / physiology
  • Cell Nucleus / metabolism
  • Cell Nucleus / microbiology
  • Cytosol / immunology
  • Cytosol / metabolism
  • Cytosol / microbiology
  • Disease Resistance / genetics*
  • Edible Grain / genetics
  • Edible Grain / immunology*
  • Edible Grain / microbiology
  • Gene Expression Regulation, Plant*
  • Plant Cells / immunology
  • Plant Cells / metabolism
  • Plant Cells / microbiology
  • Plant Diseases / genetics
  • Plant Diseases / immunology*
  • Plant Diseases / microbiology
  • Plant Proteins / genetics
  • Plant Proteins / immunology*
  • Plant Stems / genetics
  • Plant Stems / immunology*
  • Plant Stems / microbiology
  • Plants, Genetically Modified
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Tobacco / genetics
  • Tobacco / immunology
  • Tobacco / microbiology
  • Triticum / genetics
  • Triticum / immunology*
  • Triticum / microbiology

Substances

  • Plant Proteins