Anthocyanins in woody ornamental plants: biosynthesis, regulatory networks, and trade-offs in stress adaptation.

Anthocyanins are important flavonoid metabolites that are instrumental to plant adaptation to adverse environmental conditions. Increasing evidence has shown that both biotic and abiotic stresses can markedly affect anthocyanin biosynthesis and accumulation, thereby influencing plant defense capacity, stress tolerance, and metabolic reprogramming. In addition to serving as pigments, anthocyanins contribute to plant protection through multiple mechanisms, including reactive oxygen species (ROS) scavenging, metal chelation, photoprotection, and the modulation of stress-related signaling pathways. In ornamental plants, particularly woody ornamentals, anthocyanins not only determine key aesthetic traits such as flower and leaf coloration, but also serve as critical components of the stress defense system. However, compared with herbaceous model plants, the regulatory networks and functional roles of anthocyanins in these species remain insufficiently studied. This review comprehensively explores the molecular regulatory mechanisms of anthocyanin accumulation in woody plants under various stresses. These include biotic stresses (e.g., pathogenic bacteria and insect pests) and abiotic stresses (e.g., drought, salinity, extreme temperatures, heavy metals, and light stress). Furthermore, the dynamic response characteristics of anthocyanins under combined multiple stresses and their potential applications in stress-tolerance breeding are also discussed, providing a theoretical foundation for developing anthocyanin-based strategies to enhance stress tolerance in ornamental horticulture.