Functional Analysis of Two Flavanone-3-Hydroxylase Genes from Camellia sinensis: A Critical Role in Flavonoid Accumulation

Abstract

Flavonoids are major secondary metabolites in <i>Camellia sinensis</i>. Flavanone-3-hydroxylase (F3H) is a key enzyme in flavonoid biosynthesis in plants. However, its role in the flavonoid metabolism in <i>C. sinensis</i> has not been well studied. In this study, we cloned two <i>F3H</i>s from <i>C. sinensis</i>, named <i>CsF3Ha</i> and <i>CsF3Hb</i>, where <i>CsF3Ha</i> containing 1107 bases encoded 368 amino acids, and <i>CsF3Hb</i> containing 1071 bases encoded 357 amino acids. Enzymatic activity analysis showed both recombinant CsF3H enzymes in <i>Escherichia coli</i> could convert naringenin and eriodictyol into dihydrokaempferol (DHK) and dihydroquercetin (DHQ), respectively. The expression profiles showed that <i>CsF3Ha</i> and <i>CsF3Hb</i> were highly expressed in the tender leaves of tea plants. Under different abiotic stresses, the two <i>CsF3H</i>s were induced remarkably by ultraviolet (UV) radiation, sucrose, and abscisic acid (ABA). In the seeds of <i>CsF3H</i>s transgenic <i>Arabidopsis thaliana</i>, the concentration of most flavonol glycosides and oligomeric proanthocyanidins increased significantly, while the content of monocatechin derivatives decreased. The present study revealed that <i>CsF3H</i>s played critical roles in flavonoid biosynthesis in tea plants.