Brassinosteroid Potentiates Cold-Induced Transcriptome–Metabolome Reprogramming in Tea Plant Leaves: An Integrated Multi-Omics Landscape

Low temperatures severely restrict tea plant (Camellia sinensis) growth and yield stability, yet how brassinosteroid (BR) signaling modulates cold acclimation at a systems level remains insufficiently defined. Here, we integrated transcriptomic and UHPLC–MS metabolomic profiling of tea leaves under Control, 24-epibrassinolide (EBR), Cold, and Cold + EBR treatments to delineate BR-potentiated cold responses. Principal component analyses revealed clear treatment-specific separation and tight clustering of biological replicates at both omics levels. Quantitatively, cold stress induced extensive reprogramming (4075 differentially expressed genes (DEGs) and 298 differentially accumulated metabolites (DAMs)), whereas EBR alone exerted relatively modest effects (231 DEGs and 50 DAMs). Notably, EBR under cold conditions further reshaped cold-responsive networks (371 BR-modulated DEGs and 17 BR-modulated DAMs), consistent with a potentiating role for BR signaling. Functional enrichment analyses highlighted phenylpropanoid metabolism and hormone signal transduction as core responsive modules, with coordinated activation of key gateway genes (PAL, C4H, and 4CL) and concurrent engagement of lignin-, flavonoid-, and catechin-associated branches under Cold + EBR. Metabolomic analyses identified flavonoids as the dominant responsive metabolite class (49.31%), particularly anthocyanins and flavonol glycosides. Integrative TF–metabolite–gene correlation networks prioritized WRKY transcription factors (TEA001162, TEA027058) and a UDP-glycosyltransferase gene (TEA025792) as candidate hub genes linking hormone signaling to phenylpropanoid outputs. Collectively, this work provides a systems-level framework of co-regulated transcript–metabolite modules and candidate molecular targets, offering a foundation for functional validation and practical improvement of cold resilience in tea production.