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

• Published in: Proceedings of the National Academy of Sciences - PNAS 2016-09, Vol.113 (36), p.10204-10209
• Main Authors: Cesari, Stella, Moore, John, Chen, Chunhong, Webb, Daryl, Periyannan, Sambasivam, Mago, Rohit, Bernoux, Maud, Lagudah, Evans S., Dodds, Peter N.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Apoptosis; Basidiomycota - pathogenicity; Basidiomycota - physiology; Biological Sciences; Cell Nucleus - metabolism; Cell Nucleus - microbiology; Crops; Cytosol - immunology; Cytosol - metabolism; Cytosol - microbiology; Disease Resistance - genetics; Edible Grain - genetics; Edible Grain - immunology; Edible Grain - microbiology; Fungal infections; Gene Expression Regulation, Plant; Life Sciences; Microbiology and Parasitology; Nicotiana - genetics; Nicotiana - immunology; Nicotiana - microbiology; Phytopathology and phytopharmacy; Plant Cells - immunology; Plant Cells - metabolism; Plant Cells - microbiology; Plant diseases; 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; Proteins; Sequence Alignment; Sequence Homology, Amino Acid; Signal transduction; Triticum - genetics; Triticum - immunology; Triticum - microbiology; Vegetal Biology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1605483113

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.