Phenotypic, physicochemical and transcriptomic responses of Camellia sinensis cv. 'Huangjinya' to UV-B stress

Ultraviolet-B (UV-B) is an important environmental factor that seriously affects the biological process of Camellia sinensis cv. 'Huangjinya', which is highly susceptible to light stress. To understand the mechanism adapted to UV-B, we analyzed the phenotypical, physicochemical and transcriptomic responses of 'Huangjinya' in response to UV-B stress in this study. Phenotypic analysis revealed that UV-B induced a yellowing of 'Huangjinya' leaves, accompanied by a significant reduction in chlorophyll and carotenoid content. Physiological assessments showed a marked decline in photosynthetic capacity, with decreased photosynthetic rate, stomatal conductance, and electron transfer rate, alongside increased non-photochemical quenching. Antioxidant enzyme activities, particularly peroxidase (POD), were significantly reduced, while stress-responsive hormones such as abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) were elevated. Under UV-B exposure, a total of 15,170 differentially expressed genes (DEGs) were identified, with 3565 upregulated and 11,605 downregulated genes. These DEGs were primarily involved in metabolic pathways related to pigment biosynthesis, photosynthesis, antioxidant enzymes, phenylpropanoid biosynthesis, and plant hormone signal transduction. Transcriptomic analysis further indicated downregulation of genes associated with chlorophyll and carotenoid biosynthesis, as well as photosynthesis-related genes, while genes involved in flavonoid biosynthesis and stress hormone pathways were upregulated. Additionally, UV-B exposure led to a decrease in free amino acids, caffeine, and soluble sugar content, but an increase in tea polyphenols. These findings suggest that UV-B enhances the ornamental value of 'Huangjinya' leaves but adversely affects photosynthetic efficiency and the accumulation of key quality components in tea leaves. The study provides a comprehensive understanding of the molecular and physiological mechanisms underlying response to UV-B stress of 'Huangjinya', highlighting the interplay between gene expression and physiological changes in UV-B adaptation.