Influence of shading intensity on chlorophyll, carotenoid and metabolites biosynthesis to improve the quality of green tea: a review

•Shading can enhance the accumulation of chlorophylls and carotenoids in tea leaves•Shading directly influences the biosynthesis of tea quality-related metabolites•Shading intensity on tea plants can increases theanine abundance in new shoots•Decreased light intensity can increase the production of tea aromatic compounds Tea plant (Camellia sinensis L.) is an economically important beverage crop cultivated worldwide. Tea is the most popular non-alcoholic beverage, which is manufactured from fresh shoots of tea plants. The aroma, taste and color of tea are the most important index for determining tea quality. Manipulating light transmission by shading is the most effective method of improving the nutritional value and sensory qualities of tea. Shading on tea plant enhances the taste and aroma of tea by affecting the synthesis of free amino acids, flavonoids and aromatic compounds. Also, shading can significantly increase the chlorophyll content of tea leaves, leading to enhanced tea leaf coloration. Thus, the expression of genes related to chlorophyll biosynthesis, free amino acids biosynthesis and flavonoids biosynthesis pathways are significantly regulated by shading treatment to increase the overall quality of tea plants. However, the shading-induced regulatory mechanism remains unclear. Therefore, this review summarizes up to date knowledge of the shading effects on chlorophyll, carotenoid and quality-related metabolites biosynthesis for improvement of taste, aroma and color quality of green tea.