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

Abstract

Tea (Camellia sinensis) 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 qGCI6.2. Within the QTL’s confidence interval, two shikimate dehydrogenases (CsSDH4, CsSDH3) were identified. These enzymes catalyze gallic acid (GA) production from 3-dehydroquinate dehydratase, thereby contributing to galloylated catechins accumulation. RT-qPCR analysis revealed that CsSDH4 and CsSDH3 expression levels and GA and galloylated catechins contents were positively correlated. Furthermore, overexpressing CsSDH4 and CsSDH3 in transgenic tomato plants markedly increased GA and galloylated catechin contents. RNA-seq analysis of transgenic tomato indicated that CsSDH4 and CsSDH3 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.