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.

Phytosulfokine (PSK) is a tyrosine-sulfated pentapeptide found throughout the plant kingdom, playing key roles in plant growth, development, and responses to biotic and abiotic stresses. However, there is still a lack of a comprehensive analysis of the CsPSK gene family in Camellia sinensis. In this study, we conducted a genome-wide identification and characterized 14 CsPSK genes in tea plants, which are unevenly distributed across seven chromosomes. CsPSK genes encode proteins ranging from 75 to 124 amino acids in length, all belonging to the PSK-α type and containing conserved PSK domains. A synteny analysis revealed that the expansion of the CsPSK gene family is primarily attributed to whole-genome duplication, with homology to Arabidopsis thaliana PSK genes. A promoter region analysis identified cis-regulatory elements related to hormone and stress responses. An expression profile analysis showed that CsPSK genes are highly expressed in roots, stems, flowers, and leaves, and are induced by both biotic and abiotic stresses. Furthermore, an RT-qPCR assay demonstrated that the expression levels of CsPSK8, CsPSK9, and CsPSK10 are significantly upregulated following Discula theae-sinensis infection. These findings establish a basis for further research into the role of the CsPSK gene family in tea plant disease resistance and underlying molecular mechanisms, offering valuable perspectives for developing novel antimicrobial peptides.

Xyloglucan endotransglucosylase/hydrolases (XTHs) are key cell-wall-remodeling enzymes that mediate xyloglucan modification, cell expansion, and organ elongation, yet the composition and variation in the XTH gene family across tea accessions remain unclear. In this study, we systematically identified and comparatively analyzed the XTH gene family across the genomes of nine tea accessions, yielding 477 putative XTH genes. Phylogenetic, conserved-motif, protein-domain, and conserved catalytic-motif analyses indicated that the major structural features of tea XTH proteins are broadly conserved, whereas orthogroup-based presence–absence variation (PAV) analysis revealed core, variable, and accession-specific components within the family. Using transcriptomic expression profiles across eight tissues, we selected eight CsXTH genes for internode expression analysis. Reverse transcription quantitative PCR (RT-qPCR) showed that all eight genes were expressed at significantly higher levels in the third internode (I3) than in the second internode (I2) in ‘Longjing 43’ (LJ43), and CsXTH27 retained the same internode-associated expression pattern in ‘Baihaozao’ (BHZ) and ‘Zhongcha 108’ (ZC108), supporting its selection for functional analysis. Transient overexpression of CsXTH27 significantly increased the lengths of I2, I3, and I4, as well as the total length of I1–I4, compared with the empty-vector control. This phenotype was accompanied by significantly increased XTH protein content in stems and an apparent tendency toward larger pith parenchyma cell profiles. Overall, these findings reveal both structural conservation and accession-level variation in the tea XTH gene family and provide preliminary functional evidence linking CsXTH27 to shoot internode elongation.