Two shikimate dehydrogenases play an essential role in the biosynthesis of galloylated catechins in tea plants

Tea (<i>Camellia sinensis</i>) is widely cultivated throughout the world for its unique flavor and health benefits. Galloylated catechins in tea plants serve as important secondary metabolites that play a pivotal role in tea taste determination and pharmacological effects. However, the genetic basis of galloylated catechins traits remains elusive. We identified a stable and major-effect quantitative trait locus (QTL) associated with galloylated catechins index (GCI), designated <i>qGCI6.2</i>. Within the QTL's confidence interval, two shikimate dehydrogenases (<i>CsSDH4</i>, <i>CsSDH3</i>) were identified. These enzymes catalyze gallic acid (GA) production from 3-dehydroquinate dehydratase, thereby contributing to galloylated catechins accumulation. Quantitative real-time PCR (RT-qPCR) analysis revealed that <i>CsSDH4</i> and <i>CsSDH3</i> expression levels and GA and galloylated catechins contents were positively correlated. Furthermore, overexpressing <i>CsSDH4</i> and <i>CsSDH3</i> in transgenic tomato plants markedly increased GA and galloylated catechin contents. RNA-seq analysis of transgenic tomato indicated that <i>CsSDH4</i> and <i>CsSDH3</i> primarily regulate genes related to shikimic acid and flavonoid pathways, and jointly promote galloylated catechins synthesis. Our findings have further elucidated the galloylated catechins synthesis pathway and provided a theoretical basis for cultivation of tea cultivars with high galloylated catechin contents.