Integrated Metabolome and Transcriptome Analysis Reveals the Key Bitter Substances of Pleioblastus amarus Shoots at Different Developmental Stages

Pleioblastus amarus (bitter bamboo) shoots are a traditional forest vegetable in China, renowned for its nutritional composition and associated health benefits. This study aimed to investigate the dynamic changes in nutritional quality and bitterness-related metabolites, as well as corresponding gene expression in P. amarus shoots at three distinct growth stages, specifically at heights of 10 cm (BT1), 20 cm (BT2), and 40 cm (BT3). The results showed that the content of soluble sugars decreased while the content of total phenols and flavonoids, which contribute to bitterness, increased during the growth of P. amarus shoots. In addition, comparative analysis of BT2 vs. BT1, BT3 vs. BT1, and BT3 vs. BT2 revealed 14, 43, and 36, respectively, differentially accumulated metabolites (DAMs). Notably, BT2 exhibited upregulation of flavonoids, such as apigenin, while bitter amino acids, including phenylalanine and arginine, showed a marked increase in BT3. Moreover, differential gene expression analysis revealed 3161, 13268, and 3742 differentially expressed genes (DEGs) in the BT2 vs. BT1, BT3 vs. BT1, and BT3 vs. BT2 comparisons, respectively. An integrated analysis of metabolomic and transcriptomic data indicated that the metabolites and genes associated with the biosynthesis pathways of phenylalanine, tyrosine, tryptophan, arginine, and the branched-chain amino acids valine, leucine, and isoleucine were significantly enriched during the growth of P. amarus shoots. The study indicates that early-stage (≤20 cm) P. amarus shoots are mainly bitter due to flavonoids like apigenin, while the bitterness in later-stage (around 40 cm) shoots is largely due to bitter amino acids such as phenylalanine, arginine, valine, and isoleucine. This research highlights key compounds and genes related to bitterness, providing a basis for future research on enhancing the nutritional value and flavor of P. amarus shoots.