Anthocyanin accumulation in fruit crops: a multi-layered regulatory network integrating molecular, epigenetic, hormonal and environmental regulation.

Anthocyanins are key flavonoid pigments responsible for the red, blue and purple colouration of many fruit crops and play important roles in determining fruit quality, nutritional value and stress tolerance. Beyond their contribution to visual appeal, anthocyanins function as potent antioxidants that protect plant cells against diverse abiotic stresses, including high light, temperature extremes and oxidative damage. The biosynthesis of anthocyanins occurs as an extension of the flavonoid biosynthetic pathway and is regulated by complex genetic and molecular networks that integrate developmental signals with environmental cues. Central to this regulation are transcriptional complexes composed of MYB, bHLH and WD40 proteins that coordinate the expression of structural genes in the anthocyanin biosynthetic pathway. In addition to transcriptional control, emerging evidences highlight the importance of epigenetic regulation, post translational modification of regulatory proteins and cellular mechanisms governing anthocyanin transport and vacuolar sequestration. Environmental factors such as light, temperature, nutrient availability and cellular pH further influence anthocyanin biosynthesis and stability, particularly under conditions of climate variability. This review synthesizes current advances in understanding the molecular and environmental regulation of anthocyanin biosynthesis in fruit crops and presents a multi-layered regulatory framework while discussing the emerging approaches, including multi-omics and genome editing. However, a major challenge remains in the adoption of genome editing techniques in fruit crops, where genetic complexity including polyploidy and allele redundancy limits precise trait improvement, highlighting the need for more efficient molecular breeding strategies to improve pigment stability and climate resilience in fruit production systems.