Integrative Multi-Omics Elucidates the Molecular Mechanisms Underlying Sweet-Mellow Taste Formation During Withering of Niangniang Tea (Large-Leaf Yellow Tea).

Withering is a critical but poorly understood step in yellow tea processing. This study integrated metabolomics (ultra-performance liquid chromatography-tandem mass spectrometry, UPLC-MS/MS), transcriptomics (RNA sequencing, RNA-seq), and sensory evaluation to investigate dynamic changes in key metabolites and gene expression during withering (0-10 h) of Niangniang tea (NNT). Transcriptomic analysis was performed on leaves sampled directly during withering, while metabolomic profiling and sensory evaluation were conducted on finished teas processed from the corresponding withered leaves. A total of 1064 metabolites were identified. Sensory evaluation showed that 8 h of withering yielded the highest sweet-mellow taste scores. Theanine, L-aspartic acid, and L-arginine peaked at 8 h, while galloylated catechins decreased. Key regulatory genes (CsTA, CsSCPL, CsPDX2.1) were identified, with expression patterns correlating with sweet-related amino acid accumulation and catechin conversion. Integrative analysis delineated a molecular roadmap in which downregulation of CsPDX2.1 after 6 h was associated with reduced theanine hydrolysis, and upregulation of CsTA correlated with galloylated catechin conversion, collectively contributing to sweet-mellow taste. These findings provide a scientific basis for optimizing withering duration in large-leaf yellow tea production.