Genomic and metabolomic insights into the selection and differentiation of bioactive compounds in citrus

Bioactive compounds are playing an increasingly prominent role in breeding functional and nutritive fruit crops such as citrus. However, the genomic and metabolic basis for the selection and differentiation underlying bioactive compounds variations in citrus remain poorly understood. Here, we constructed a species-level variation atlas of genomes and metabolomes using 299 citrus accessions. A total of 19,829 significant SNPs were targeted to 653 annotated metabolites, among which multiple significant signals were identified for secondary metabolites, especially flavonoids. Significantly differential accumulation of bioactive compounds in phenylpropane pathway, mainly flavonoids and coumarins, were unveiled across ancestral citrus species during differentiation, which is likely associated with the divergent haplotype distribution and/or expression profiles of relevant genes, including p-coumaroyl coenzyme A 2'-hydroxylases, flavone synthases, cytochrome P450 enzymes, prenyltransferases and UDP-glycosyltransferases. Moreover, we elucidated the citrus varieties with excellent antioxidant and anticancer capacities, clarifying the robust associations between distinct bioactivities and specific metabolites. Thus, these findings provide citrus breeding options for enrichment of beneficial flavonoids and avoidance of the potential risk of coumarins. This study will illuminate the application of genomic and metabolic engineering strategies in developing modern healthy citrus cultivars.