Integrated Metabolomics and Transcriptomics Reveal Bitter Compounds and Synthetic Pathways in the Special-Germplasm...

Bamboo shoots represent a traditional food in China, with most varieties exhibiting a bitter taste; however, understanding of the compounds responsible for this bitterness remains limited. In this study, shoots of a special-germplasm bitter-tasting Dendrocalamus brandisii (Dbs) were investigated, using sweet-tasting Dendrocalamus brandisii (Db) shoots as a control. Electronic tongue analysis, broad-target metabolomics, targeted metabolomics, and transcriptomics were employed to identify the metabolites and key genes associated with bitterness in Dbs shoots. Electronic tongue measurements revealed a significant difference in bitterness between the two groups. Human sensory evaluation confirmed that Dbs was perceived as significantly more bitter and less sweet than Db (p < 0.01). Nontargeted metabolomics screening identified 43 differential metabolites, 19 of which were upregulated in Dbs. Targeted analysis of these differential metabolites, combined with the BitterDB database and previously reported bitter compounds, suggested that 4-Hydroxybenzoate, gallic acid, epicatechin, tryptophan, histidine, and apigenin may contribute to the bitterness of Dbs. Among these, 4-Hydroxybenzoate showed an approximately 92-fold higher content in Dbs compared to Db. The taste activity values (TAVs) of the identified bitter compounds were calculated; only 4-Hydroxybenzoate exhibited a TAV greater than 1 (14.581), while the TAV of the other compounds were all below 1. Integrating broad-target metabolomics, targeted metabolomics, and TAV analysis, 4-Hydroxybenzoate was inferred to be one of the primary bitter substances. Transcriptomic analysis indicated significant upregulation of key genes in the biosynthetic pathway of 4-Hydroxybenzoate, including PAL, 4CL, and C4H. Enzyme activity assays further demonstrated that phenylalanine ammonia-lyase, 4-coumarate-CoA ligase, and cinnamate 4-hydroxylase activities were markedly higher in Dbs than in Db. RT-qPCR validation confirmed that the expression levels of 4CL3, 4CL4, PAL1, PAL2, PAL3, PAL4, and PTAL were significantly elevated in Dbs, consistent with the transcriptomic data. In conclusion, 4-Hydroxybenzoate is proposed as the most likely key compound responsible for the bitterness in Dbs shoots. This study provides valuable insights into the bitterness formation mechanism in this Dbs and offers important information for the improvement of its edible quality.