Metabolomics and transcriptomics reveal metabolites and genes associated with the bitterness and astringency in sweet potato tips

Sweet potato tips are a potential vegetable with special flavor and high nutrients, but only the leafy type is popular among consumers, while most types of sweet potato tips are not widely accepted as a vegetable due to their bitter and astringent taste. Here, to reveal the biological pathway involved in the formation of bitter and astringent compounds in sweet potato tips, metabolomics and transcriptomics were performed for three sweet potato varieties with different levels of bitterness and astringency. Metabolomics analysis revealed that 139 metabolites might be related to both bitterness and astringency of sweet potato tips, and 31 flavonoid glycosides and hydroxycinnamic acid derivatives may synergistically affect bitterness and astringency. Histidine, alkaloids, and terpenoids specifically determine bitterness, while flavonol/flavone glycosides and seven phenolic acid derivatives specifically affect astringency. Transcriptome analysis identified 46 structural genes and 24 transcription factors responsible for the accumulation of bitter and astringent compounds, which were then used to construct the biosynthetic pathways. Two bHLHs were identified as hub genes in biosynthetic pathways of bitterness, and four MYBs and one bHLH were common transcription factors in the biosynthetic pathways of both bitterness and astringency. This study provides valuable insights into the formation mechanisms of bitter and astringent taste in sweet potato tips and important information for improvement of leafy type sweet potato.