Protein Phosphorylation: An Essential Role in Shoot Apical Meristem Homeostasis

The shoot apical meristem (SAM) serves as the cellular source of aboveground plant development and is precisely regulated by a complex interplay of genetic, hormonal, and environmental factors. Central to this regulation is the CLAVATA3 (CLV3)–WUSCHEL (WUS) negative feedback loop, which maintains SAM homeostasis by balancing stem cell proliferation and differentiation. Among the diverse regulatory mechanisms, reversible protein phosphorylation, which is mediated by protein kinases and phosphatases, has emerged as a key posttranslational modification that integrates internal and external signals to modulate SAM activity. This review summarizes recent advances in understanding the roles of kinases and phosphatases in SAM maintenance, with a particular focus on phosphorylation-mediated control of the CLV3–WUS pathway and associated signaling networks. By synthesizing these molecular insights, we aim to provide a comprehensive reference for deciphering the regulatory mechanisms underlying SAM homeostasis. A deeper understanding of SAM regulation not only advances fundamental knowledge of plant developmental biology but also holds significant potential for improving crop architecture and agricultural productivity.