Multiomics analysis unravels a UV-B-mediated regulatory network of anthocyanin biosynthesis in lettuce (Lactuca sativa L.).

The production of nutrient-dense lettuce (Lactuca sativa) in greenhouse systems is often constrained due to the depletion of solar UV-B radiation. While UV-B exposure is empirically associated with elevated anthocyanin levels, the underlying molecular regulatory network remains poorly understood. Here, we performed integrated metabolomic and transcriptomic analyses to characterize the metabolic and transcriptomic profiles of lettuce grown under UV-sufficient open-field and UV-deficient greenhouse conditions. Multiomics analysis revealed a strong positive correlation between ambient UV-B exposure and anthocyanin accumulation, confirming UV-B signal as a key elicitor of this metabolic process. Co-expression network analysis identified LsHY5a/b as central regulators downstream of UV-B signaling. LsHY5a/b act upstream of LsMYB113b, establishing a transcriptional cascade that regulates anthocyanin biosynthesis. Transient expression assays further demonstrated that LsMYB113b positively regulates anthocyanin accumulation by directly binding to the promoters of LsCHS1, LsCHI3, LsF3H, and LsANS to activate their transcription. Collectively, our results elucidate the molecular mechanism by which UV-B induces anthocyanin accumulation via the LsHY5a/b-LsMYB113b transcriptional cascade. This work also provides a feasible strategy to enhance anthocyanin production in UV-deficient greenhouse systems, thereby improving the nutritional quality of horticultural crops in controlled environments.