DcMYB30 negatively function in drought tolerance of Dendrobium catenatum by modulating flavonoid biosynthesis

Drought stress is a severe abiotic stress, limiting the plant growth, development and yield. MYB transcription factor family plays a crucial role in plants response to adversity stress, particularly drought. However, a comprehensive analysis of the MYB gene family in Dendrobium catenatum remains limited, especially regarding the functions of two-repeat MYB proteins in response to drought stress and their regulation of flavonoid biosynthesis and accumulation. Here, severe drought stress inhibited the growth of D. catenatum and decreased polysaccharides and flavonoid contents. This study identified 174 MYB genes and characterized their phylogenetic relationships, protein profiles, and expression patterns. Co-expression analysis and transient expression assay revealed that an R2R3-MYB DcMYB30 was a key regulator in drought response and flavonoid synthesis in D. catenatum. DcMYB30 was found to localize in the nucleus and was down-regulated by drought stress. In both DcMYB30-overexpressing Nicotiana benthamiana or D. catenatum, flavonoid content decreased and transcript levels of multiple flavonoid biosynthetic enzyme-coding genes were downregulated. According to these findings, it is proposed that DcMYB30 may negatively regulate flavonoid biosynthesis by down-regulating flavonoid pathway enzyme-coding genes (e.g., 4CL), thereby reducing the flavonoid biosynthesis or accumulation and drought tolerance in D. catenatum. This study provides fundamental insights for characterizing the physiological roles of two-repeat MYB transcription factors in plant stress responses.