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 glucosino- lates 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 valu- able tool for systematically investigating glu- cosinolate 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 K. Lu  J. Li (&) Chongqing Rapeseed Engineering Research Center, College of Agronomy and Biotechnology, Academy of Agricultural Sciences, Southwest University, Beibei, Chongqing 400715, PR China e-mail: ljn1950@swu.edu.cn R. Snowdon Department of Plant Breeding, Justus Liebig University, Giessen, Germany in Arabidopsis thaliana. Among these glucosinolate-related genes, transcription fac- tor, 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 glucosino- late profiles and total seed glucosinolate con- tents in B. napus and its parental species. These results, together with those published previ- ously, provide a valuable resource for under- standing 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.