Phosphoprotein Phosphatases (PPP), Important Molecular Switchers in Plant Cell and Environment Responses

Protein phosphatases, the executors of protein dephosphorylation, play indispensable roles in plant growth, development, and stress adaptation. This review summarizes the classification and biological functions of plant protein phosphatases, with a specific focus on the phosphoprotein phosphatase (PPP) family. By forming dynamic holoenzyme complexes with diverse regulatory subunits, PPP precisely controls vital cellular processes such as hormone signalling pathways, cell division, and light responses. Recent studies highlight the critical involvement of PPP in immune defence and abiotic stress adaptation, including drought and salt tolerance. Although PP1 and PP2A are extensively studied in non-plant systems, functionally dissecting PPP in plants remains an essential frontier, particularly in elucidating isoform-specific functions, mapping regulatory subunit-substrate-kinase networks, and decoding post-translational modifications. Looking forward, integrating phosphoproteomics with advanced toolkits, such as TurboID proximity labelling, AP-MS, substrate-trapping mutants, as well as single-cell and spatial omics, alongside bioinformatics, will be pivotal in overcoming these challenges. Ultimately, engineering regulatory subunit-PPP-substrate modules for crop improvement. Given that protein phosphatases are emerging as a pivotal regulatory hub for balancing the growth-defence trade-off, unravelling their multifaceted roles will simultaneously advance fundamental plant biology and drive innovations in precision breeding.