Transcriptome analysis reveals the effects of red and blue light on the physiological and medicinal components of Dendrobium denneanum

Different wavelengths of light have significant effects on plant growth and chemical composition. Previous studies found that red and blue combined light (2 R/3B) can significantly affect the growth of Dendrobium denneanum Kerr and the synthesis of secondary metabolites. However, the optimal treatment time and influencing mechanism are not clear. In this study, D. denneanum was treated with irradiation for 4 h (A), 8 h (B) and 12 h (C) every day. Changes in physiological, biochemical and active components were observed, and RNA-Seq analysis was carried out. The results showed that the treatment time of 8 h could increase the plant height, stem diameter, leaf number, chlorophyll and carotenoid content, increase the activities of POD and SOD and reduce the content of MDA. Moreover, treatment B for 60 days significantly increased the flavonoid content, and treatment B for 120 days was conducive to the accumulation of polysaccharides. Transcriptomic analysis showed that there were 3410 differentially expressed genes between the B treatment and CK, of which 1681 genes were upregulated and 1729 genes were downregulated. The GO and KEGG databases were used to analyze the enrichment of metabolic pathways of differential genes. It was found that they were significantly enriched in plant hormone signal transmission, phenylpropanoid biosynthesis, and start and cross metabolism. RT-qPCR verified seven randomly selected differential genes (DELLA, EBF1/2, PP2C, SAUR, CcOAOMT, POD and UGT). The results were consistent with the results of transcriptome sequencing. This research provides a new perspective for studying the regulation of light quality on the growth and medicinal components of D. denneanum.