Protein Phosphatase 5 Promotes SUMM2-Mediated Immunity by Facilitating Its Protein Accumulation

Protein Phosphatase 5 (PP5) is an evolutionarily conserved serine/threonine phosphatase with a unique tetratricopeptide domain. It has been implicated in a wide range of cellular processes in mammals, but its function in plants is unknown. Here, we uncovered that Arabidopsis PP5 is required for immunity mediated by the nucleotide-binding leucine-rich repeat immune receptor protein SUMM2. Loss-of-function mutations in PP5 suppress the autoimmune phenotypes caused by the activation of SUMM2 due to the disruption of the MEKK1-MKK1/MKK2-MPK4 kinase cascade. Further biochemical analysis revealed that SUMM2 interacts with Heat Shock Protein 90 (HSP90) and PP5, and SUMM2 level is reduced in pp5 knockout mutant plants, suggesting that PP5 promotes the accumulation of SUMM2, likely through its association with the HSP90 chaperone complex.