Effects of Light Intensity and Spectral Composition on the Transcriptome Profiles of Leaves in Shade Grown Tea Plants (Camellia sinensis L.) and Regulatory Network of Flavonoid Biosynthesis

Black net shade treatment attenuates flavonoid biosynthesis in tea plants, while the effect of light quality is still unclear. We investigated the flavonoid and transcriptome profiles of tea leaves under different light conditions, using black nets with different shade percentages, blue, yellow and red nets to alter the light intensity and light spectral composition in the fields. Flavonol glycosides are more sensitive to light intensity than catechins, with a reduction percentage of total flavonol glycosides up to 79.6% compared with 38.7% of total catechins under shade treatment. A total of 29,292 unigenes were identified, and the KEGG result indicated that flavonoid biosynthesis was regulated by both light intensity and light spectral composition while phytohormone signal transduction was modulated under blue net shade treatment. PAL, CHS, and F3H were transcriptionally downregulated with light intensity. Co-expression analysis showed the expressions of key transcription factors MYB12, MYB86, C1, MYB4, KTN80.4, and light signal perception and signaling genes (UVR8, HY5) had correlations with the contents of certain flavonoids (p < 0.05). The level of abscisic acid in tea leaves was elevated under shade treatment, with a negative correlation with TFG content (p < 0.05). This work provides a potential route of changing light intensity and spectral composition in the field to alter the compositions of flavor substances in tea leaves and regulate plant growth, which is instructive to the production of summer/autumn tea and matcha.