Integrated Physiological and Omics Responses of Red Lettuce (Lactuca sativa) Driven by Varying Light Spectrum: Insights into Anthocyanin Synthesis

The health benefits of anthocyanins for humans are well established. However, the influence of spectral light composition in plant factories on plant growth and anthocyanin biosynthesis remains poorly understood. This study selected red lettuce as a model plant due to its high anthocyanin content. Using a plant factory with artificial lighting, we applied three light treatments: control (R: B=160:40), T1 (R:B: G=130:20:50) and T2 (R:B: G=75:75:50) to examine their effects on plant physiology and anthocyanin production. A multi-omics analysis further identified potential pathways and genes regulating anthocyanin synthesis under different light conditions. Plants under T2 had higher levels of anthocyanins, flavonoids, phenolics, and carotenoids. Conversely, fresh and dry biomass, total leaf area, chlorophyll content, and sugar levels were higher in red lettuce leaves grown under T1. 110 anthocyanidin metabolites and 573 genes showed differential expression under different light combinations. Transcriptomic analysis revealed a substantial increase in the activity of genes related to anthocyanin precursors, such as PAL and 4-CL, as well as structural genes involved in anthocyanin synthesis, including F3H, DFR, ANS, and UDP glucosyltransferase, specifically under T2. Furthermore, our findings identified 14 transcription factors, comprising 4 bHLH, 3 MYB, 3 bZIP and 4 WRKY genes, which could play crucial roles in regulating anthocyanin biosynthesis. These findings lay the groundwork for investigating the molecular mechanisms underlying anthocyanin biosynthesis in lettuce leaves. Moreover, they provide valuable insights that could contribute to advancements in leaf color genetics for lettuce production in plant factories.