Transcription Factor CsDOF3 Mediates Light‐Dependent Antagonistic Regulation of Theanine and Catechin Accumulation in Tea Plants

Light intensity critically modulates the accumulation of secondary metabolites in tea plants (Camellia sinensis), yet the regulatory mechanisms that coordinate the opposing responses of theanine (a nitrogen-rich amino acid) and catechins (carbon-rich flavonoids) remain poorly understood. Here, we identify CsDOF3, a light-responsive DOF (DNA-binding with one finger) transcription factor, as a candidate regulator influencing both metabolic pathways. Across a light intensity gradient of 5000-15 000 lx, CsDOF3 expression increases with light intensity, correlating with decreased theanine and increased catechin accumulation. Functional analyses demonstrate that overexpression of CsDOF3 suppressed theanine biosynthesis while promoting catechin synthesis, whereas virus-induced gene silencing produced the opposite phenotype. Mechanistically, CsDOF3 binds to the promoters of CsTSI (theanine synthetase 1, a key theanine biosynthetic gene) and CsANS (anthocyanidin synthase, a catechin biosynthetic gene) in vitro, with opposite effects on their transcriptional activity in dual-luciferase assays. Collectively, these findings suggest that CsDOF3 is a candidate regulator linking light conditions to the accumulation of theanine and catechins, providing a framework for understanding light-mediated regulation of tea flavour-related metabolites.