Amino acid transporter CsBAT links GABA accumulation to flavonoid metabolism in <i>Camellia sinensis</i>

γ-Aminobutyric acid (GABA), a four-carbon non-protein amino acid functions as a key signaling molecule in plants. As a signature bioactive compound in tea, GABA plays a crucial role in determining both flavor profile and health-promoting properties. Despite its importance, the molecular regulation of GABA accumulation in tea plants-especially its metabolic crosstalk with key quality determinants like flavonoids-remains elusive. While amino acid transporters are known to mediate source-sink allocation in plants, the functional characterization of GABA transporters in <i>Camellia sinensis</i> has been lacking. In this study, we identified and functionally characterized the bidirectional amino acid transporter CsBAT in tea plants. Through a comprehensive multiplatform validation system encompassing yeast heterologous expression, <i>Arabidopsis</i> genetic transformation, and tea transgenic system, we revealed that <i>CsBAT</i> shows vascular-specific expression and facilitates directional amino acid transport from source (mature leaves) to sink (young shoots), thereby significantly boosting GABA accumulation in buds and young leaves. Importantly, we discovered that CsBAT functionally interacts with key flavonoid biosynthetic enzymes (LAR, 4CL, C4H) within secondary metabolic networks. Our findings provide the first mechanistic link between <i>CsBAT</i>-mediated amino acid transport and tea quality formation, establishing both theoretical frameworks and practical tools for molecular breeding of premium tea cultivars.