Identification of the bHLH gene family in Dracaena cambodiana reveals candidate genes involved in flavonoid biosynthesis

The basic helix-loop-helix (bHLH) transcription factors (TFs) regulate multiple biological processes by altering the expression of target genes. However, the bHLH superfamily genes in the dragon tree (Dracaena cambodiana Pierre ex Gagnep) have not been characterized, and their role in flavonoid biosynthesis remain unclear. Here, 62 bHLH genes in D. cambodiana were identified, and these genes were classified into 19 subfamilies based on a phylogenetic comparison with proteins from Arabidopsis. Transcriptomic analysis revealed that 8 DcbHLHs were up-regulated when exposed to the inducer of dragon's blood and ultraviolet radiation b (UVB). Interaction network analysis revealed that 3 bHLHs (DcbHLH2, DcbHLH5 and DcbHLH56) are likely involved in flavonoid biosynthesis. In addition, DcbHLH5 and flavonoids biosynthetic genes were co-expressed in response to the inducer and UVB exposure. Furthermore, DcbHLH5 could bind to the promoters of flavonoid biosynthesis genes and activate their expression. This study suggests that DcbHLH proteins maybe involved in flavonoid biosynthesis.