Glucosinolate biochemical diversity and innovation in the Brassicales

Glucosinolates were analysed from herbarium specimens and living tissues from representative of all families of the Brassicales, following the phylogenetic schemes of Rodman et al. (1998) and Hall et al. (2002, 2004), including specimens of Akania, Setchellanthus, Emblingia, Stixis, Forchhammeria and members of the Capparaceae for which glucosinolate content had not previously been reported. The results are reviewed along with additional published data on glucosinolate content of members of the Brassicales. In addition to providing an overview of the evolution of glucosinolate biochemical diversity within the core Brassicales, there were three main findings. Firstly, the glucosinolate content of some 'orphan' taxa of the Brassicales, such as Setchellanthus and Emblingia were consistent with recent phylogentic analyses based upon DNA sequence comparisons, while further analyses of Tirania and Stixis is required. Secondly, methyl glucosinolate is found within the Capparaceae and Cleomaceae, but also, unexpectedly, within Forchhammeria, with implications for the biochemical and evolutionary origin of methyl glucosinolate and the phylogenetic relationships of Forchhammeria. Thirdly, whereas Old World Capparaceae contain methyl glucosinolate, New World Capparaceae, including New World Capparis, either contain methyl glucosinolates or glucosinolates of complex and unresolved structures, indicative of continued innovation in glucosinolate biosynthesis. These taxa may be productive sources of glucosinolate biosynthetic genes and alleles that are not found in the model plant Arabidopsis thaliana.