UVR8-mediated regulation of anthocyanin metabolism in plants: molecular mechanisms, signaling networks, and adaptive functions.

Ultraviolet-B (UV-B) radiation is both a potential stressor and an environmental signal that reshapes plant metabolism. Anthocyanins are among the most visible UV-B-responsive metabolites, linking photoprotection, stress acclimation, pigmentation, and crop quality. UV RESISTANCE LOCUS 8 (UVR8) is the primary UV-B photoreceptor in plants, but its connection with anthocyanin metabolism remains fragmented across molecular mechanisms, physiological contexts, and applied crop systems. This review develops an integrative framework for understanding UVR8-mediated anthocyanin regulation as a context-dependent signaling-metabolic interface rather than a simple linear response to UV-B. In this framework, UV-B-activated UVR8 engages CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1)-associated signaling, enhances HY5/HYH-mediated transcriptional regulation, and connects light perception to MYB, B-box (BBX), and MYB-bHLH-WD40 (MBW) modules that control anthocyanin pathway genes. The magnitude and direction of this route are shaped by species, tissue identity, organ type, developmental stage, wavelength, UV-B dose, exposure duration, visible-light background, temperature, sugar status, phytohormones, and redox cues. Emerging evidence that naringenin chalcone selectively binds to and stabilizes monomeric UVR8 reveals a reciprocal metabolite-to-photoreceptor input, although its relationship to the canonical COP1-HY5 pathway remains unresolved. By distinguishing UV-B-induced effects, UVR8-associated responses, and genetically demonstrated UVR8 dependence, this review clarifies the evidence boundaries of the field. It also identifies key gaps, including tissue-specific UVR8 responses, crop-specific downstream modules, and dose thresholds for balancing protection, growth, and quality. A refined understanding of this interface may improve the predictability of UV-B-based strategies for photoprotection, stress resilience, fruit coloration, and crop quality improvement.