FERONIA kinase and PP2A antagonistically regulate salt tolerance in Arabidopsis

Leucine-rich repeat extensin (LRX) 3/4/5 and FERONIA (FER) jointly regulate plant salt tolerance, but the mechanisms by which LRX3/4/5 modulate FER activity in response to salt stress remain largely unclear. Here, we found that lrx345 mutations reduce FER kinase activity, which explains the phenotypic similarity between lrx345 and fer-4. Immunoprecipitation-mass spectrometry (IP-MS) analysis reveals a physical interaction between FER and protein phosphatase 2A (PP2A), with PP2A directly dephosphorylating FER. Disruption of PP2A restores FER kinase activity and salt hypersensitivity in the lrx345 mutant, establishing PP2A as a key negative regulator of FER kinase activity. Conversely, FER inhibits PP2A phosphatase activity through phosphorylation, forming a dynamic feedback loop. Further mechanistic studies show that FER and PP2A coordinately regulate plant salt tolerance by controlling auxin transport via the modulation of PIN3 phosphorylation. Collectively, our work unveils an antagonistic kinase-phosphatase pair that fine-tunes phosphorylation-dependent signaling to optimize plant adaptation to salt stress.