Transcriptomic and metabolomic profiling of tea plant under spring cold stress across severity grades

Under sudden spring cold snaps, tea shoots within the same plantation often exhibit varying degrees of chilling injury. To compare the response mechanisms of tea leaves with different cold damage levels, this study first classified spring cold‑exposed tea shoots into four grades (FT_I to FT_IV) using chlorophyll fluorescence imaging, and then systematically analyzed their physiological characteristics, metabolite accumulation, and gene expression patterns. The results showed that as cold damage severity increased, photosynthetic efficiency declined, membrane lipid peroxidation intensified, and antioxidant enzyme activities significantly decreased. Metabolomics revealed that flavonoids, amino acids and their derivatives, catechins and their derivatives, phenolic acids, and lipids play key roles in response to cold stress. Notably, 46 lipid compounds markedly accumulated in severely damaged samples. Transcriptomics identified 8 commonly enriched pathways and 18 uniquely enriched pathways across different comparisons. Integrated omics further pinpointed key co‑enriched pathways, including phenylpropanoid biosynthesis, plant hormone signal transduction, and flavonoid biosynthesis. Comparing leaves with different damage degrees, 12 metabolites (mainly amino acids and theaflavins) showed increasing accumulation patterns, while 6 metabolites (mainly glycosides) showed decreasing patterns. Furthermore, the expression patterns of five UGT genes highly correlated with five glycoside compounds were experimentally validated. This study elucidates the graded response mechanisms of tea leaves under cold stress and provides a theoretical basis and candidate markers for breeding cold‑tolerant tea plants and preventing cold damage.