Case Study for Trait-Related Gene Evolution: Glucosinolates

Abstract

Glucosinolates are a group of secondary metabolites involved in plant defense and found mainly in the Brassicales order. While the breakdown products of some glucosinolates are beneficial to human health, many glucosinolates are toxic. The recently sequenced genomes of Brassica napus and its parental species Brassica rapa and Brassica oleracea provided the Brassica scientific community with a valuable tool for systematically investigating glucosinolate biosynthesis, transport, and breakdown genes, elucidating the relationship between variation of glucosinolate profiles and the evolution of glucosinolate-related genes in Brassica crops. In this chapter, we summarized the variation in glucosinolate composition and content in Brassica crops and identified 166, 167, 191, 333 genes in B. rapa, B. oleracea var. capitata, B. oleracea var. italica, and B. napus, respectively, as orthologs of 78 glucosinolate biosynthetic, transport, and breakdown genes in Arabidopsis thaliana. Among these glucosinolate-related genes, transcription factor, side-chain modification, and breakdown genes experienced significant expansion in the four Brassica crops. Moreover, phylogenetic and expression pattern analyses of the glucosinolate-related genes HAG1, MAM, AOP, and GTR correspond with the glucosinolate profiles and total seed glucosinolate contents in B. napus and its parental species. These results, together with those published previously, provide a valuable resource for understanding the genetic mechanism underlying glucosinolate metabolism and transport and suggest novel approaches for improving the nutritional quality of Brassica crops through breeding cultivars with lower glucosinolate contents.