TITLE:
Arabidopsis thaliana Type One Protein Phosphatases: Context-Dependent Regulators of Development, Stress Responses, and Immunity
AUTHORS:
Kai Chen, Jianzhong Huang
KEYWORDS:
Type One Protein Phosphatases, Arabidopsis thaliana, Protein Phosphatase 1, Phosphorylation, Hormone Signaling, Autophagy, Immunity, Stress Response
JOURNAL NAME:
Journal of Biosciences and Medicines,
Vol.14 No.9,
September
21,
2026
ABSTRACT: Reversible protein phosphorylation enables plants to coordinate growth, stress responses, and immunity. Arabidopsis thaliana TYPE ONE PROTEIN PHOSPHATASES (TOPPs), homologs of eukaryotic protein phosphatase 1 catalytic subunits, exemplify how a highly conserved phosphatase family can generate distinct signaling outputs. The nine TOPPs are partially redundant, yet their functions are shaped by regulatory partners, substrate recruitment, expression patterns, and subcellular localization. TOPP4 dephosphorylates DELLA repressors, PIN1, and PIF5; TOPP1-associated complexes regulate ABA signaling through SnRK2s; and TOPP1, TOPP4, and TOPP5 dephosphorylate EIN2 at Ser655 to reinforce ethylene signaling. TOPP4 directly dephosphorylates ATG13a, while TOPP1, TOPP3, and TOPP9 also reduce ATG13a phosphorylation in planta; higher-order topp mutants support broader family-level redundancy during fixed-carbon starvation-induced autophagy. In immunity, TOPPs restrain basal defense, mutant TOPP4 states are monitored by the CNL receptor SUT1, and the Pseudomonas syringae effector AvrE targets TOPPs to enhance ABA-dependent water soaking. Collectively, current evidence supports a model in which catalytic redundancy is constrained by protein interactions and spatially restricted substrate access. Defining these TOPP complexes and their phosphosites may enable more selective manipulation of plant signaling than altering bulk phosphatase activity.