Recent progress in unraveling the molecular mechanisms of anthocyanin biosynthesis and regulation in tomato

Tomato (Solanum lycopersicum) is one of the most economically important vegetable crops worldwide. Fruit quality is a critical determinant of consumer preference and market value, with color being the primary visual trait. While carotenoids impart red pigmentation, anthocyanins enable the accumulation of deep purple and blue hues. Although anthocyanins have been widely studied, a comprehensive understanding of their biosynthesis and regulation in tomato is still lacking. This review therefore synthesizes current knowledge to outline the molecular mechanisms underlying these processes. We highlight the central role of the MYB-bHLH-WD40 transcriptional activation complex. Additionally, we discuss the multilayered regulatory network involving other transcription factors, such as the bZIP family members SlHY5 and SlAREB1, BBX proteins, and others. Furthermore, we elaborate on post-transcriptional and post-translational regulatory mechanisms, which fine-tune anthocyanin accumulation. Finally, we outline current challenges and future directions for enhancing tomato anthocyanins. This review serves the dual purpose of providing an updated theoretical foundation for genetic improvement in tomato and offering a regulatory framework applicable to other horticultural crops.