Lineage‐specific evolution of flavin‐containing monooxygenases involved in aliphatic glucosinolate side‐chain modification

Abstract Glucosinolates, a class of specialized metabolites specific to the order Brassicales, have diverse bioactivities that are largely dependent on the structures of their side chains. Flavin‐containing monooxygenases (FMOs) encoded by the FMO GS‐OX genes have been found to catalyze side‐chain modifications during the synthesis of methionine‐derived aliphatic glucosinolates. Seven FMO GS‐OX genes have been identified in Arabidopsis Heynh., but the evolution of these genes in the Brassicaceae, a family including many economically important vegetables, is poorly understood. In this study, the phylogenetic and syntenic relationships of the FMO GS‐OX genes belonging to 12 sequenced Brassicaceae species were analyzed. Our results showed that the FMO GS‐OX genes included two tandem arrays, the FMO GS‐OX2‐4 group (group A) and the FMO GS‐OX5‐7 group (group B). The evolutionary histories of the FMO GS‐OX groups A and B were similar across the Brassicaceae, but two lineage‐specific evolutionary routes developed after these two separate species lineages diverged from Aethionema arabicum (L.) Andrz. ex DC. In the lineage I route, FMO GS‐OX gene copies tended to increase due to frequent tandem duplication events in most species and a whole genome triplication in Camelina sativa (L.) Crantz. In the lineage II route, gene copies decreased due to deletion events. Combining these results with those of previous studies, we speculated that the FMO GS‐OX genes were derived from an ancestral gene with a broad expression distribution and a broad range of substrates, which then underwent subfunctionalization to generate progeny limited in either spatial expression or substrate structure. Furthermore, the absence of FMO GS‐OX5 substrates in some FMO GS‐OX5 ‐containing species may suggest neofunctionalization of these genes.