Transcriptome analysis of flavonoid biosynthesis in safflower flowers grown under different light intensities

BACKGROUND: Safflower (Carthamus tinctorius L.) is a domesticated species with a long history of cultivation and widespread distribution across the globe, and light plays an important role in controlling its distribution boundary. Flowers from safflower have been widely used in traditional Chinese medicine because of their ability to improve cerebral blood flow. Flavonoids are the main active compounds in safflower and have many pharmacological effects. In this study, we aimed to explore the relationship between different light intensities and flavonoid biosynthesis in safflower flowers cultivated in greenhouse. METHODS: The transcriptome of safflower flowers grown under different light intensities were sequenced through BGISEQ-500 platform. After assembled and filtered, Unigenes were annotated by aligning with seven functional databases. Differential expression analysis of two samples was performed with the DEseq2 package. Differentially expressed genes (DEGs) related with flavonoids biosynthesis were analyzed by Real-time PCR (RT-PCR). Flavonoids accumulation in flowers were determined by high performance liquid chromatography and spectrophotometer. RESULTS: Transcriptome analysis of safflower flowers cultivated under different light intensities was performed. A total of 99.16 Gb data were obtained, and 78,179 Unigenes were annotated. Among the DEGs, 13 genes were related to flavonoid biosynthesis. The differential expressions of seven key genes were confirmed by RT-PCR. In addition, the levels of some flavonoids were measured in safflower flowers grown under different light intensities. CtHCT3 gene expression showed a significantly negative correlation with kaempferol content in safflower grown under different light intensities. CONCLUSION: Our results strongly suggested that the reduction in light intensity in a suitable range promoted flavonoid biosynthesis in safflower flowers. We suggest that the expressions of HCT genes played an important role in flavonoid accumulation in safflower flowers. Our study lays a foundation for further research on the effects of light on flavonoid biosynthesis in safflower.