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

Stella Cesari, John Moore, Chunhong Chen, Daryl Webb, Sambasivam Periyannan, Rohit Mago, Maud Bernoux, Evans S Lagudah, Peter N Dodds

Proceedings of the National Academy of Sciences of the United States of America 2016 Sep 06

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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.

Citation

Stella Cesari, John Moore, Chunhong Chen, Daryl Webb, Sambasivam Periyannan, Rohit Mago, Maud Bernoux, Evans S Lagudah, Peter N Dodds. Cytosolic activation of cell death and stem rust resistance by cereal MLA-family CC-NLR proteins. Proceedings of the National Academy of Sciences of the United States of America. 2016 Sep 06;113(36):10204-9