Mechanism underlying the carotenoid accumulation in shaded tea leaves

Carotenoids contribute to tea leaf coloration and are the precursors of important aromatic compounds. Shading can promote the accumulation of carotenoids in tea leaves, but the underlying mechanism remains unknown. In the study, we analyzed the content and composition of carotenoids, and transcript levels and functions of related genes in carotenoid biosynthesis using HPLC, qRT-PCR, and heterologous expression system. It was found that long-term shading (14 days, 90% shading) significantly increased the total carotenoid content in tea leaves, and increased the expression of non-mevalonate pathway (MEP) genes (CsDXS1 and CsDXS3) and key genes in carotenoid synthesis pathway (CsPSY, CsLCYB, and CsLCYE). Long-term exposure to darkness (14 days, 0 lx) decreased the transcription of most carotenoid biosynthetic genes and adversely affected carotenoid accumulation. Furthermore, CsDXS1, CsDXS3, CsPSY, CsLCYB, and CsLCYE were functionally identified and contributed to the enhanced accumulation of carotenoids in tea leaves in response to long-term shading.