The Plant Sucrose Synthase Gene Family: Multi-Level Regulatory Networks and Functional Diversification in Plants

Sucrose synthase (SUS) is a key enzyme in plant carbon metabolism, catalyzing the reversible interconversion between sucrose + uridine diphosphate (UDP) and UDP-glucose (UDP-Glc) + fructose. It plays a central role in carbon flux allocation, cell wall and starch synthesis, as well as plant development and stress responses. SUS is encoded by a multigene family whose members exhibit significant functional diversification and expression specificity across species, tissues, and subcellular compartments. This review systematically summarizes the physiological functions of SUS in source–sink regulation, seed filling, and rapidly growing tissues; describes the organ-specific expression patterns and diverse subcellular localizations of different isoenzymes in Arabidopsis and major crops; and elucidates the phylogenetic pattern of the SUS gene family into three evolutionary clades—SUS I, SUS II, and SUS III—based on a comparative analysis of selected angiosperm species. Furthermore, it integrates the multi-level regulatory mechanisms of SUS, including transcriptional and post-transcriptional regulation, as well as the dynamic control of enzyme activity, stability, and subcellular localization through post-translational modifications such as phosphorylation and ubiquitination and protein interactions. Finally, this study identifies gaps in current research regarding ubiquitination mechanisms, metabolic network integration, and crop applications. It envisions SUS-centered molecular breeding strategies, informed by integrative regulatory genomics, multi-omics, and genome editing, to redirect crop carbon fluxes and thereby enhance yield, improve quality traits, and increase stress tolerance.