Abstract: Epigallocatechin gallate (EGCG) is an important flavor and health functional component in tea. Previous studies have found that EGCG biosynthesis in tea plants is affected by potassium nutrition, but the regulatory mechanism of its biosynthesis is currently unclear. This study used one year old tea seedlings of Huangdan as the experimental object, and set up 5 treatment groups (K1-K5), with K₂SO₄ concentrations of 0.4, 0.6, 0.8, 1.0 mmol∙L^-1 and 1.2 mmol∙L^-1 for irrigation, respectively. The joint analysis of transcriptomics and metabolomics shows that, under low-potassium treatment (K1), the flavonoid contents in the new shoots of tea plants accumulated significantly and the EGCG content reached the highest level, and the difference reached a significant level compared with that of the high potassium treatment (K5). The related metabolites of phenylalanine, cinnamic acid and p-coumaric acid on the EGCG synthesis pathway were up-regulated in the K4 or K5 treatments, whereas the downstream metabolites of the flavonoid pathway (dihydroquercetin, dihydromyricetin, colorless delphinidin pigment and epigallocatechin) were up-regulated in the K1 and K2 treatments. Under the influence of potassium nutrition, EGCG biosynthesis was positively regulated by a series of structural genes CsCHI, F3′5′H, CsF3H (CSS0019002), CsANS, CsANR, Csaro DE, CsSCPL, and transcription factor (MYB306), as well as negatively regulated by CsPAL, CsC4H, Cs4CL, CsCHS, CsF3H (CSS0016177), CsDFR (CSS0011557) and transcription factor (NAC83). It is thus clear that potassium nutrition regulates EGCG synthesis by affecting the expressions of key genes in tea plants, thereby affecting EGCG content. This study provided a scientific basis for the regulation of EGCG biosynthesis in tea plants by potassium nutrition.

Key words: potassium, EGCG, biosynthesis, tea plant