AmMYB82 promotes flavonoid accumulation and enhances drought tolerance in Astragalus membranaceus

Astragalus membranaceus is a medicinal herb extensively used in China. R2R3-MYB is one of the largest transcription factor families in plants, playing a key role in plant development and environmental stress responses. Although quite a few R2R3-MYB transcription factors from economic plants have been characterized, the biological roles of the R2R3-MYB genes in A. membranaceus remain largely unknown. Here, 123 AmR2R3-MYB members in A. membranaceus were systematically identified and their phylogenetic positions, protein and gene structures, and expression patterns were analyzed. Co-expression network analysis revealed that AmMYB82 was a key gene in regulation of flavonoid synthesis. AmMYB82 was found to localize in the nucleus and activated transcription of AmCHS. In the AmMYB82 overexpressing Arabidopsis thaliana, the content of total flavonoids increased, and the expression levels of six enzyme coding genes for flavonoid synthesis, including AmPAL, AmCHS, AmC4H, AmFLS, AmF3H, and Am4CL, were elevated. Overexpression of AmMYB82 enhanced drought tolerance of Arabidopsis seedlings. Furthermore, overexpression of AmMYB82 in A. membranaceus hairy roots increased flavonoid concentration, transcription of the corresponding enzyme genes, and drought stress tolerance. Building on these findings, we developed a working model for AmMYB82 regulating flavonoid biosynthesis and contributing to the abiotic stress response of A. membranaceus. AmMYB82 directly activated enzyme coding genes in the flavonoid biosynthesis pathway such as AmCHS, promoting flavonoid accumulation and increasing drought tolerance. This research enhanced our knowledge of the biological functions of R2R3-MYB genes and provided candidate genes for the genetic breeding of A. membranaceus.