HighlightDuring Pseudomonas syringae infection the MAPK phosphatase AP2C1 negatively regulates plant resistance and modulates defense responses, such as changing hormone levels, callose deposition and transcriptional reprogramming.

HighlightIn plant immunity against nematodes, MPK3/6 act positively and their activity is controlled by the MAPK phosphatase AP2C1. The MAPK activation pattern suggests the attenuation of defence signalling during nematode infection.

Mitogen-activated protein kinase (MAPK) cascades transmit environmental signals and induce stress and defence responses in plants. These signalling cascades are negatively controlled by specific phosphatases of the type 2C Ser/Thr protein phosphatase (PP2C) and dual-specificity phosphatase (DSP) families that inactivate stress-induced MAPKs; however, the interplay between phosphatases of these different types has remained unknown. Our work reveals that different Arabidopsis MAPK phosphatases, the PP2C-type AP2C1 and the DSP-type MKP1, exhibit both specific and overlapping functions in plant stress responses. Each single mutant and ap2c1 mkp1 double mutant displayed enhanced stress-induced activation of MAPKs MPK3, MPK4, and MPK6, as well as induction of a set of transcription factors. Moreover, ap2c1 mkp1 double mutants show an autoimmune-like response, associated with elevated levels of the stress hormones salicylic acid and ethylene, and of the phytoalexin camalexin. Interestingly, this phenotype is reduced in ap2c1 mkp1 mpk3 and ap2c1 mkp1 mpk6 triple mutants, suggesting that the autoimmune-like response is due to MAPK misregulation. We conclude that the evolutionarily distant MAPK phosphatases AP2C1 and MKP1 contribute crucially to the tight control of MAPK activities, ensuring appropriately balanced stress signalling and suppression of autoimmune-like responses during plant growth and development.