Multiomics Analysis Revealed the Role of LsBBX22–LsHY5a/b Module in Promoting UV–B-Mediated Anthocyanin Accumulation in Lettuce

Ultraviolet-B (UV–B) radiation profoundly affects plant photomorphogenesis and secondary metabolism, yet its regulatory role in lettuce ( Lactuca sativa ) remains poorly understood. We conducted metabolome and transcriptome analyses to reveal the molecular basis of UV–B adaptation in highland-grown lettuce. Flavonoid accumulation was enhanced as a key adaptive strategy for UV–B acclimation. The key UV–B signaling components LsHY5a / b showed positive correlations with ten LsBBXs and flavonoid/anthocyanin-related genes. UV–B treatment rapidly induced the transcription of LsHY5a / b and LsBBX22-1 . LsBBX22-1 physically interacted with LsHY5a/b. While LsBBX22-1 activated the expression of anthocyanin-related genes, it could not bind directly to their promoters. By contrast, LsHY5a/b directly bound to the promoters of LsCHS1, LsCHI3, and LsF3H . Thus, LsBBX22 and LsHY5a/b acted synergistically to regulate UV–B-induced anthocyanin biosynthesis. This study clarified the molecular mechanism of the LsBBX22-1–LsHY5a/b module in promoting UV–B-induced anthocyanin accumulation in lettuce, providing a theoretical basis for cultivating high-quality vegetables in highland regions.