Integrated Transcriptomic and Metabolomic Analysis of the Snap Bean Pod Fiber Mutant (bfm) Identifies Candidate Genes Associated with Pod Wall Fiber Accumulation

Background and aims: Snap bean is a widely planted legume vegetable crop in the world, with tender pods as its edible organ. In the actual production process, excessive fiber content in bean pods can lead to a deterioration in their taste after cooking, seriously affecting their edible quality. In order to better study the mechanism of fiber formation in bean pod walls, we selected a bean pod fiber mutant (bfm) from the bean mutant library. Methods: Fiber content determination, cytological observation, and transcriptome and metabolome analysis were performed on the pod walls of mutant bfm and its wild-type at different developmental stages. Key results: The results showed that the crude fiber content of the bfm pod wall tissue was significantly higher than that of the wild type during the mature commercial pod stage, and cellulose may be the main factor causing the increase in fiber content in the bean pod wall. During the mature commercial pod stage, the number of cells in the pod wall tissue of bfm increased significantly compared to the wild type, with an increase in phloem fibers and thicker cell walls. It is speculated that this situation led to changes in fiber content in the mutant bfm. The combined analysis of transcriptome and metabolome showed that differentially expressed genes and metabolites were enriched in metabolic pathways and secondary metabolite biosynthesis pathways. Several metabolites, including glycine, L-glutamine, D-arabinitol, and D-ribose, were associated with the expression of Phvul.007G077800 (CTL) and Phvul.003G089600 (KOR). Conclusions: These genes and metabolites may participate in coordinated metabolic pathways that influence the availability of substrates and energy required for cellulose biosynthesis, thereby potentially contributing to cellulose accumulation in the pod wall. This study provides theoretical research on the mechanism of fiber synthesis in bean pod walls, and also to provide some reference for bean breeding improvement and application practice.