Effect of shading on trichome formation and CAPRICE-like gene expression in tea (Camellia sinensis var. sinensis) leaves

Tea (Camellia sinensis var. sinensis) is one of the most popular beverages worldwide and is highly regarded for its unique taste and health benefits. The traditional practice of shading tea plants before harvest is employed to ensure the production of high-quality Japanese green tea. However, the precise effects of shading on trichome formation, leaf tissue structure, and the expression of related genes remain largely unknown. In the present study, we conducted a comparative analysis to investigate the effect of shading on the aforementioned aspects of tea leaves. Our findings revealed a significant decrease in the number of trichomes in the youngest 1st stage leaves under shaded conditions compared with that under full-light conditions. Histological analyses revealed that epidermal cells in tea leaves under shaded conditions were thinner, further indicating the influence of light on leaf structures. To delve deeper into the regulatory mechanisms, the expression levels of six Camellia sinensis CAPRICE (CsCPC) genes encoding R3 MYB transcription factors, which have been implicated in trichome formation in tea plants, were examined using real-time reverse transcription PCR. Among the six genes, CsCPC-1, Camellia sinensis ENHANCER OF TRY AND CPC 1–2 (CsETC1–2), and CsETC3 exhibited increased expression under shaded conditions, indicating their potential involvement in the light-mediated regulation of tea leaf characteristics. The expression levels of the phenylpropanoid pathway structural genes Camellia sinensis cinnamic acid 4-hydroxylase (CsC4H), Camellia sinensis cinnamoyl CoA reductase (CsCCR), and Camellia sinensis flavanone 3′ hydroxylase (CsF3′H), were significantly reduced under shaded conditions, suggesting the regulation of phenylpropanoid content. Our study demonstrated that shading treatment induces significant changes in the number of trichomes in younger leaves, alters the width of epidermal cells, and affects the expression levels of CsCPCs and genes related to the phenylpropanoid pathway. These findings have the potential to enhance tea leaf quality, and offer pragmatic implications for tea farming.