Dissection of Cell Death Induction by Arabidopsis thaliana CC-NBS-LRR Receptor SUT1 and Its Interacting Protein TOPP4 Mutant in Nicotiana benthamiana

Nucleotide-binding and leucine-rich repeat receptors (NLRs) play an important role in plant innate immunity. Previous reports indicate that SUT1 (SUPPRESSOR OF TOPP4 1) is required for the autoimmune response mediated by TYPE ONE PROTEIN PHOSPHATASE 4 (TOPP4) mutation topp4-1 (namely TOPP4^T246M) in <i>Arabidopsis</i>. We observed that co-expression of SUT1 with TOPP4 mutant versions, instead of wild-type TOPP4, produced robust cell death in <i>N. benthamiana</i>. The YFP-labeled SUT1 was localized on the plasma membrane (PM), and Gly2, Cys4, and Ser6 are crucial amino acid sites for its PM localization and function. Further dissection proclaimed that the function and localization of SUT1 are influenced by mutations in conserved specific residues. These findings may provide a new perspective for elucidating the activation mechanism of SUT1.