Advances in mechanisms of anthocyanin transport in fruit

Anthocyanin, a natural water-soluble pigment, influences various fruit quality traits, including visual appearance and nutritional value. The biosynthesis of anthocyanin occurs through a series of enzymatic reactions in the endoplasmic reticulum, followed by transport to the vacuole for storage. Considerable research has elucidated the biosynthesis pathway and transcriptional regulation of anthocyanin over the past several decades. Moreover, key structural and regulatory genes participating in the pathway have been characterized in a variety of fruit species. However, the molecular mechanisms underlying the transmembrane transport of anthocyanin after synthesis remain unclear. Here, we review current progress on anthocyanin transport and discuss the three main transport models: glutathione S-transferase, membrane transporters, and vesicle trafficking. Despite numerous hypotheses, various questions concerning the dynamic transport and aggregation of anthocyanin in the vacuole remain to be answered. Understanding the molecular mechanisms and regulatory networks of anthocyanin transport will not only expand our knowledge regarding the anthocyanin metabolic pathway, but also provide a theoretical basis and molecular tools for improving fruit quality traits in breeding programs.