Type one protein phosphatases (TOPPs) catalyze EIN2 dephosphorylation to regulate ethylene signaling in Arabidopsis

Type one protein phosphatases (TOPPs) widely modulate phytohormone signaling and stress responses, but their roles in ethylene signaling remain unknown. This study reveals a reciprocal regulatory relationship between TOPPs and ethylene insensitive 2 (EIN2)-mediated ethylene signaling. We identified that ethylene can induce TOPPs' expression, and topp1/4/5 mutants exhibited partial ethylene insensitivity with reduced EIN3 protein. Mechanistically, TOPPs function upstream of EIN2 and interact with its carboxyl-terminal domain (CEND) to dephosphorylate the S655 residue. This site-specific dephosphorylation promotes EIN2 stability and EIN2 CEND nuclear accumulation, thereby activating ethylene responses. Notably, EIN2^S655A-YFP/ein2-5 plants displayed constitutive ethylene responses and improved salt tolerance. Further investigation showed that EIN3/EIN3 like 1 (EIL1) activates TOPPs' expression by binding to their promoters, amplifying ethylene signaling accordingly. Together, our finding establishes TOPPs as key regulators in ethylene signaling and reveal a dephosphorylation switch mechanism governing EIN2 function, providing critical insight into how EIN2 posttranslational modifications mediate plant stress adaptation.