VC1 catalyses a key step in the biosynthesis of vicine in faba bean

Faba bean (Vicia faba L.) is a widely adapted and high-yielding legume cultivated for its protein-rich seeds(1). However, the seeds accumulate the pyrimidine glucosides vicine and convicine, which can cause haemolytic anaemia (favism) in 400 million genetically predisposed individuals(2). Here, we use gene-to-metabolite correlations, gene mapping and genetic complementation to identify VC1 as a key enzyme in vicine and convicine biosynthesis. We demonstrate that VC1 has GTP cyclohydrolase II activity and that the purine GTP is a precursor of both vicine and convicine. Finally, we show that cultivars with low vicine and convicine levels carry an inactivating insertion in the coding sequence of VC1. Our results reveal an unexpected, purine rather than pyrimidine, biosynthetic origin for vicine and convicine and pave the way for the development of faba bean cultivars that are free of these anti-nutrients. Vicine and convicine are the main anti-nutritional factors restricting the consumption of faba bean. Transcript profiling combined with metabolite profiling was applied to identify a key enzyme responsible for the biosynthesis of vicine and convicine in faba bean.

Automated summary

Vicine and convicine, which can cause haemolytic anaemia in genetically predisposed individuals, are the main anti-nutritional factors in faba bean seeds. The key enzyme VC1, identified through gene-to-metabolite correlations and genetic complementation, plays a crucial role in biosynthesis of vicine and convicine. Cultivars with low levels of these compounds have an inactivating insertion in the coding sequence of VC1.