Transcriptomics and metabolomics reveal the adaptive mechanisms of Gracilariopsis lemaneiformis in response to blue light

The marine macroalgae Gracilariopsis lemaneiformis was cultured as the raw material of agar and abalone feed in China with the yield of 368,967 tons dry mass. As light quality is the most important environmental factor for the photosynthetic organism, and blue light is a main spectrum for photosynthesis and metabolite accumulation in plants, we test blue light for their effects on the G. lemaneiformis. Results showed that the relative growth rate of G. lemaneiformis decreased while the principal economical metabolites, including agar, polysaccharides were accumulated significantly under blue light. To further understand the response mechanism of G. lemaneiformis to blue light, the omics analysis was used, which revealed that blue light redirected metabolic pathways toward the synthesis of diverse primary and secondary metabolic products, divided into four categories, including photosynthesis, antioxidant system, energy metabolism and carbohydrate synthesis. Among them, the genes encoding photosynthetic pigments and phycobiliproteins increased significantly, but the carbon fixation pathway, the ASA-GSH cycle, and TCA cycle were down-regulated, and more carbon flowed into the synthesis pathway of agar and polysaccharides, which were consistent with the changes of physiological parameters. These findings helped us to understand the mechanism of G. lemaneiformis responding to blue light and provide a new perspective for the culture of high-agar content G. lemaneiformis.