Physiological and multi-omics insights into ultraviolet B-induced stress adaptation in Fritillaria cirrhosa native to the Qinghai-Tibet Plateau

INTRODUCTION: Fritillaria cirrhosa (Liliaceae), an endangered medicinal plant of the Qinghai-Tibet Plateau, exhibits strong adaptability to ultraviolet B (UV-B) radiation during the transition from wild to artificial habitats. However, the molecular and physiological mechanisms underlying these adaptive responses remain largely unexplored, which hinders efforts to enhance their conservation and cultivation. OBJECTIVES: The aim of this study was to comprehensively examine the morphological, cellular, and physiological responses of cultivated F. cirrhosa to UV-B radiation, with a particular focus on uncovering the key defense mechanisms that confer enhanced plant resilience. METHODS: To simulate its native high-altitude habitat, we augmented the growing area with ultraviolet radiation. Wild type F. cirrhosa was used as a control to systematically evaluate the response of cultivated plants to UV-B radiation, focusing on their morphology, cytology, and physiology. Multi-omics analyses were employed to uncover the transcriptional regulatory networks governing the responses of cultivated plants to UV-B stress. RESULTS: UV-B radiation induced substantial microstructural damage to the leaf mesophyll, chloroplasts, and stomatal complexes in both wild type and cultivated F. cirrhosa. However, the cultivated type exhibited significantly enhanced ability to maintain reactive oxygen species (ROS) homeostasis, effectively activating the antioxidant defense system and promoting the biosynthesis of UV-absorbing metabolites-thereby ensuring superior photosynthetic performance under UV-B stress. Mechanistically, upon UV-B detection, UVR8 photoreceptors in cultivated F. cirrhosa rapidly interact with the light regulatory protein COP1, forming the UVR8-COP1 complex, which stabilizes the light-signal transcription factor HY5 and modulates the activity of the FcMYB and FcWRKY transcription factors. This regulatory cascade promotes the biosynthesis of flavonoids and lignin, enhancing the transcription of key genes, namely FcPAL, Fc4CL, FcC4H, FcCHS, and FcF3H. This results in the accumulation of key phenolic compounds (xanthohumol, chrysin, luteolin, galangin, and pinocembrin) that function as "sunscreens" and "ROS scavengers", thereby effectively reducing UV-B-induced oxidative stress. CONCLUSION: Compared to the wild type F. cirrhosa, the cultivated type demonstrated heightened UV-B tolerance through the activation of the UVR8-COP1-HY5 signaling pathway and increased biosynthesis of phenolic compounds. These insights provide a strong foundation for breeding strategies and conservation efforts to safeguard this valuable highland species.