VC2regulates baseline vicine content in faba bean

Abstract

AbstractFaba bean (Vicia faba) is a valuable legume crop desired globally for its high nutritional composition. However, the seed vicine and convicine (v-c) content reduces the nutritional quality of faba bean protein and can induce favism in individuals with glucose-6-phosphate dehydrogenase deficiency. Recently,VC1gene, encoding a bi-functional riboflavin protein, was reported to be responsible for initiating the biosynthetic pathway inV. faba. In low v-c cultivars, a 2 bp insertion in this gene results in a loss of function, but the mutation only partially eliminates v-c biosynthesis, indicating the involvement of other genes. Here, we demonstrate that a novelV. fabariboflavin gene,VC2, is responsible for the residual v-c contents in faba bean.VC2shares nearly identical functional domains withVC1and has GTP cyclohydrolase II activity, catalyzing the conversion of GTP into an intermediate molecule in the biosynthetic pathway. Gene expression analysis reveals thatVC2contributes a minor effect to the trait, accounting for approximately 5-10% of total riboflavin gene transcripts which significantly correlates with the baseline contents in low v-c cultivars. Our results illustrate that cultivars carrying the 2 bp inactivating insertion inVC1still have residual v-c levels due toVC2activity. Furthermore, we find thatVC1has multiple alleles and exhibits copy number variations, complicating molecular marker development. Conversely, single nucleotide polymorphisms withinVC2provide a reliable alternative for marker-assisted selection in faba bean breeding. In conclusion, our study elucidates the complex genetic regulation of v-c biosynthesis and provides valuable insights to facilitate its elimination in faba bean.