The phosphatase PP2C12 is a negative player in LRX-RALF-FER-mediated cell wall integrity sensing

Plants have evolved an elaborate cell wall integrity (CWI) sensing system to monitor and modify cell wall formation. LRR-extensins (LRXs) are cell wall-anchored proteins that bind RAPID ALKALINIZATION FACTOR (RALF) peptide hormones and induce compaction of cell wall structures. At the same time, LRXs form a signaling platform with RALFs and the transmembrane receptor kinase FERONIA (FER) as a means to relay changes in CWI to the protoplast. LRX1 of Arabidopsis thaliana is predominantly expressed in root hairs and lrx1 mutants develop defective root hairs. Here, we identify a regulator of LRX1-RALF-FER signaling as a suppressor of the lrx1 root hair phenotype. The repressor of lrx1_23 (rol23) gene encodes PP2C12, a type 2C phosphatase of clade H that interacts with FER and dephosphorylates Thr696 in the FER activation loop in vitro. The LRX1-related function of PP2Cs appears clade H-specific and was not observed for other PP2Cs investigated. Collectively, our data suggest that LRX1 acts upstream of the RALF1-FER signaling module and PP2C12 has an inhibitory activity via modulating FER activity to fine-tune CWI signaling.