GENETICS OF ALIPHATIC GLUCOSINOLATES .1. SIDE-CHAIN ELONGATION IN BRASSICA-NAPUS AND ARABIDOPSIS-THALIANA

Aliphatic glucosinolates are thioglucosides synthesized by genera with in the Capparales including Arabidopsis and Brassica. They have been s hown to mediate pest or pathogen interactions and to reduce the feedin g quality of rapeseed meal. Their biological activity is largely depen dent upon the structure of the side chain which determines the nature of hydrolysis products produced following tissue damage. A generalized model of the biosynthesis of aliphatic glucosinolates is proposed and tested with reference to the genetic regulation of side chain length by analysing recombinant populations of B. napus and A. thaliana devel oped from parental lines which varied in their glucosinolate content. The results of the B. napus studies were consistent with a model in wh ich alleles at a single locus (Gsl-pro) regulate the presence or absen ce of propyl glucosinolates, and those at two other loci (Gsl-elong-C and Gsl-elong-A) (which map onto a pair of homoeologous linkage groups , one from the C genome and one from the A genome) regulate side chain elongation of the amino acid derivative which results in the producti on of butyl and pentyl glucosinolates. As null alleles do not occur at the Gsl-elong-A locus, the proportion of propyl glucosinolates is lim ited to below 30 per cent of total aliphatic glucosinolates. Alleles a t a single locus in A. thaliana (Gsl-elong-Ar), which maps 1.3 cM from the RFLP locus m291 on chromosome 5, regulate side chain elongation o f aliphatic glucosinolates in this species. It is suggested that the G sl-elong-Ar gene is homologous to the Gsl-elong-A and Gsl-elong-C gene s and, if cloned, could be used to downregulate the endogenous Gsl-elo ng genes in B. napus.