Mechanisms of silicon-mediated amelioration for <i>Camellia sinensis</i> using physiology, transcriptomics, and metabolomics under cold stress

Cold stress significantly impacts the growth, quality, and yield of tea plant leaves. Additionally, silicon (Si) is a widely abundant element on earth and is recognized for its beneficial effect on plant growth and development. Here, a comprehensive transcriptomic, biochemical, and metabolomic investigations on tea plant leaves was conducted, examining the impact of Si-mediated improvement during short- (1 d), medium- (3 d), and long-term (5 d) exposure to cold stress. Biochemical and physiological analyses demonstrated that Si-mediated amelioration enhanced the activity of protective enzyme systems during all three cold stress treatments. There was a marked increase in soluble sugar content and a significant decrease in chlorophyll B content during the medium-term cold stress. Integrated transcriptomic and metabolomic analyses revealed that the differentially expressed genes (DEGs) primarily targeted pathways in phenylpropane biosynthesis, α-linolenic acid metabolism, pentose and glucuronic acid interconversion, and nitrogen metabolism. Similarly, differentially abundant metabolites (DAMs) linked to cold stress response in tea plants predominantly involved flavone and flavonol biosynthesis, flavonoid biosynthesis, aminoacyl-tRNA biosynthesis, galactose metabolism, and phenylpropanoid biosynthesis. The integrated analysis of the metabolites associated with these pathways and expression profiles further confirmed the involvement of the identified DEGs in responding to cold stress and the beneficial effect of Si in tea plants. This research expands our knowledge of the regulatory networks underlying cold stress responses in tea plants.