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.