Flower power and the mustard bomb: Comparative analysis of gene and genome duplications in glucosinolate biosynthetic pathway evolution in cleomaceae and brassicaceae

Abstract

PREMISE OF THE STUDY: Glucosinolates (GS) are a class of plant secondary metabolites that provide defense against herbivores and may play an important role in pollinator attraction. Through coevolution with plant-interacting organisms, glucosinolates have diversifi ed into a variety of chemotypes through gene sub- and neofunctionalization. Polyploidy has been of major importance in the evolutionary history of these gene families and the development of chemically separate GS types. Here we study the eff ects of polyploidy in Tarenaya hassleriana (Cleomaceae) on the genes underlying GS biosynthesis. METHODS: We established putative orthologs of all gene families involved in GS biosynthesis through sequence comparison and their duplication method through calculation of synonymous substitution ratios, phylogenetic gene trees, and synteny comparison. We drew expression data from previously published work of the identifi ed genes and compared expression in several tissues. KEY RESULTS: We show that the majority of gene family expansion in T. hassleriana has taken place through the retention of polyploid duplicates, together with tandem and transpositional duplicates. We also show that the large majority (>75%) is actively expressed either globally or in specifi c tissues. We show that MAM and CYP83 gene families, which are crucial to GS diversifi cation in Brassicaceae, are also recruited into specifi c tissue expression pathways in Cleomaceae. CONCLUSIONS: Many GS genes have expanded through polyploidy, gene transposition duplication, and tandem duplication in Cleomaceae. Duplicate retention through these mechanisms is similar to A. thaliana, but based on the expression of GS genes, Cleomaceae-specifi c diversifi cation of GS genes has taken place.