# The Arabidopsis phosphatase PP2C12 negatively regulates LRX-RALF-FER-mediated cell wall integrity sensing

## TL;DR

This study identifies PP2C12 as a negative regulator of a signaling pathway that helps plants sense and respond to changes in their cell wall structure.

## Contribution

The paper discovers that PP2C12, a clade H phosphatase, inhibits the FER receptor kinase to regulate cell wall integrity signaling in Arabidopsis.

## Key findings

- PP2C12 interacts with and dephosphorylates FER at Thr696, modulating its activity.
- Phosphorylation of FER at Thr696 is essential for suppressing the root hair defects in lrx1 mutants.
- PP2C12 negatively regulates the LRX1-RALF-FER signaling module involved in cell wall integrity sensing.

## Abstract

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. LRXs also form a signaling platform with RALFs and the transmembrane receptor kinase FERONIA (FER) to maintain cell wall integrity. 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 clade H phosphatase that interacts with FER and dephosphorylates Thr696 in the FER activation loop in vitro. Expression of FER phospho-mimetic and phospho-null mutants in an lrx1 fer-4 background demonstrates that phosphorylation of FER at Thr696 is essential for suppression of lrx1 phenotypes by rol23. The LRX1-related function of PP2Cs appears clade H-specific. Collectively, our data suggest that LRX1 acts upstream of the RALF-FER signaling module and that PP2C12 inhibits FER via activation-loop dephosphorylation.

Outside the plant cell plasma membrane leucine-rich repeat extensins (LRX), together with rapid alkalinization factor (RALF) peptides and their receptor FERONIA, inform growth processes about the properties of the cell wall. Here, this module is found to be negatively regulated by the phosphatase PP2C12 dephosphorylating FERONIA.

The defect in root hair development of the Arabidopsis lrx1 (lrr-extensin 1) mutant is suppressed by rol23 (repressor of lrx1_23).rol23 is mutated in PP2C12, a phosphatase of the clade H of PP2C-type phosphatases.PP2C12 binds the receptor kinase FER and dephosphorylates Thr696, which in turn modulates FER activity.LRX1 and FER together generate a growth signal, and PP2C12 is a negative regulator in this process.

The defect in root hair development of the Arabidopsis lrx1 (lrr-extensin 1) mutant is suppressed by rol23 (repressor of lrx1_23).

rol23 is mutated in PP2C12, a phosphatase of the clade H of PP2C-type phosphatases.

PP2C12 binds the receptor kinase FER and dephosphorylates Thr696, which in turn modulates FER activity.

LRX1 and FER together generate a growth signal, and PP2C12 is a negative regulator in this process.

Phosphorylated receptor kinase FERONIA allows LRR-extensin 1 to sense cell wall integrity.