A genus-specific R2R3 MYB transcription factor, CsMYB34, regulates galloylated catechin biosynthesis in Camellia sinensis

Abstract

Galloylated catechins are the dominant polyphenols in Camellia sinensis (L.) O. Kuntze. The mechanisms responsible for accumulation of these specialized metabolites in tea plants remains unclear. This paper presents an extended member of subgroup 5 of transcription factors R2R3-MYB, CsMYB34, as a critical gene specifically regulating galloylated catechin biosynthesis. CsMYB34 has a TT2-type motif [VIRTKATRCSKVFIP]. Its transcription levels were positively correlated with galloylated catechin content in 19 tea varieties, with correlation coefficients ≥0.79. Suppression of CsMYB34 expression caused a significant decrease in galloylated catechin content, as well as reduced expression levels of the key galloylated catechin biosynthesis gene CsSCPL4. Yeast one-hybrid (Y1H), electrophoretic mobile shift assay (EMSA) and dual-luciferase reporter system (DLR) showed that CsMYB34 interacts directly with the promoter region of CsSCPL4, thereby upregulating its transcription. This research indicates that the CsMYB34 transcription factor selectively modulates the biosynthetic pathway of galloylated catechins, thereby offering a plausible rationale for the observed elevated levels of these compounds in tea leaves.