Light control of catechin accumulation is mediated by photosynthetic capacity in tea plant (Camellia sinensis)

Abstract

Background: Catechins are crucial in determining the flavour and health benefits of tea, but it remains unclear that how the light intensity regulates catechins biosynthesis. Therefore, we cultivated tea plants in a phytotron to elucidate the response mechanism of catechins biosynthesis to light intensity changes.

Results: In the 250 μmol·m^{- 2}·s^{- 1} treatment, the contents of epigallocatechin, epigallocatechin gallate and total catechins were increased by 98.94, 14.5 and 13.0% respectively, compared with those in the 550 μmol·m^{- 2}·s^{- 1} treatment. Meanwhile, the photosynthetic capacity was enhanced in the 250 μmol·m^{- 2}·s^{- 1} treatment, including the electron transport rate, net photosynthetic rate, transpiration rate and expression of related genes (such as CspsbA, CspsbB, CspsbC, CspsbD, CsPsbR and CsGLK1). In contrast, the extremely low or high light intensity decreased the catechins accumulation and photosynthetic capacity of the tea plants. The comprehensive analysis revealed that the response of catechins biosynthesis to the light intensity was mediated by the photosynthetic capacity of the tea plants. Appropriately high light upregulated the expression of genes related to photosynthetic capacity to improve the net photosynthetic rate (Pn), transpiration rate (Tr), and electron transfer rate (ETR), which enhanced the contents of substrates for non-esterified catechins biosynthesis (such as EGC). Meanwhile, these photosynthetic capacity-related genes and gallic acid (GA) biosynthesis-related genes (CsaroB, CsaroDE1, CsaroDE2 and CsaroDE3) co-regulated the response of GA accumulation to light intensity. Eventually, the epigallocatechin gallate content was enhanced by the increased contents of its precursors (EGC and GA) and the upregulation of the CsSCPL gene.

Conclusions: In this study, the catechin content and photosynthetic capacity of tea plants increased under appropriately high light intensities (250 μmol·m^{- 2}·s^{- 1} and 350 μmol·m^{- 2}·s^{- 1}) but decreased under extremely low or high light intensities (150 μmol·m^{- 2}·s^{- 1} or 550 μmol·m^{- 2}·s^{- 1}). We found that the control of catechin accumulation by light intensity in tea plants is mediated by the plant photosynthetic capacity. The research provided useful information for improving catechins content and its light-intensity regulation mechanism in tea plant.

Keywords: Catechin biosynthesis; Light intensity; Photosynthetic capacity; Tea plant.