Dynamic Accumulation and Transcriptional Regulation of Alkylamides in Developing Zanthoxylum planispinum var. Dintanensis Fruits

The accumulation dynamics and regulatory mechanisms of the alkylamides, the key pungent compounds in the fruits of Sichuan peppers, remain poorly understood. Using fruits of the Zanthoxylum planispinum var. dintanensis (Dintan) harvested at five key developmental stages, we comprehensively mapped the accumulation of numbering compounds and their underlying molecular drivers by integrating HPLC-based metabolite profiling and de novo transcriptomics. Total alkylamide content increased during development, with hydroxyl-α-sanshool (HαSS) being predominant. The contributions of hydroxyl-β-sanshool (HβSS) and hydroxyl-ε-sanshool (HεSS) increased in later stages. Cluster and correlation analyses identified 51 candidate genes strongly correlated (|r| ≥ 0.6) with HαSS accumulation, predominantly enriched in fatty acid and branched-chain amino acid metabolism pathways. The expression patterns of five stearoyl-CoA desaturase (SCD) genes, one long-chain acyl-CoA synthetase (ACSL/fadD), and one S-(hydroxymethyl)glutathione dehydrogenase/alcohol dehydrogenase (frmA) gene closely mirrored HαSS accumulation. In contrast, 3-oxoacyl-[acyl-carrier-protein] synthase II (fabF) and one β-ketoacyl-CoA synthase (KCS) gene exhibited a negative correlation. Accordingly, a positive regulatory network was constructed for HαSS accumulation. These findings revealed key candidate targets for deciphering the molecular basis of its unique flavor and for breeding high-pungency cultivars.