Plant responses to UV-B radiation: physiology, transcription, epigenetics, and secondary metabolism

Ultraviolet-B (UV-B) radiation, a biologically active component of sunlight, profoundly influences plant physiology, growth, and metabolism. In this review, we integrate current understanding of how plants perceive and adapt to UV-B stress through multilayered regulatory networks. At the physiological level, UV-B exposure elicits dose-dependent effects ranging from enhanced photoprotection and secondary metabolite accumulation at low doses to oxidative damage and growth inhibition under high-intensity conditions. Central to UV-B perception is the photoreceptor UVR8, which activates signaling cascades involving COP1, HY5, and MYB transcription factors to regulate gene expression and promote photomorphogenesis and flavonoid biosynthesis. Concurrently, plants utilize UVR8-independent pathways, such as MAPK and PIKK cascades, to mitigate DNA damage and activate stress responses. Epigenetic modifications, particularly DNA methylation and histone acetylation, further modulate UV-B-responsive gene expression and contribute to stress memory and transgenerational adaptation. We also elucidate the transcriptional networks and non-coding RNAs involved in secondary metabolite biosynthesis, particularly those enhancing flavonoid production. Finally, we discuss emerging applications of UV-B signaling in crop improvement and outline future directions including multi-omics integration, epigenetic inheritance mechanisms, and real-time UV-B monitoring technologies. Together, these insights reveal the intricate mechanisms by which plants adapt to UV-B radiation and provide a basis for leveraging UV-B responses in agriculture and plant biotechnology.