Genetics of aliphatic glucosinolates. I. Side chain elongation in Brassica napus and Arabidopsis thaliana

Abstract

Aliphatic glucosinolates are thioglucosides synthesized by genera within the Capparales including Arabidopsis and Brassica. They have been shown to mediate pest or pathogen interactions and to reduce the feeding quality of rapeseed meal. Their biological activity is largely dependent 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 developed from parental lines which varied in their glucosinolate content. The results of the B. napus studies were consistent with a model in which alleles at a single locus (Gsl-pro) regulate the presence or absence 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 production of butyl and pentyl glucosinolates. As null alleles do not occur at the Gsl-elong-A locus, the proportion of propyl glucosinolates is limited to below 30 per cent of total aliphatic glucosinolates. Alleles at a single locus in A. thaliana (GsIelong-Ar), which maps 1.3 cM from the RFLP locus m291 on chromosome 5, regulate side chain elongation of aliphatic glucosinolates in this species. It is suggested that the Gsl-elong-Ar gene is homologous to the Gsl-elong-A and Gsl-elong-C genes and, if cloned, could be used to downregulate the endogenous Gsl-eiong genes in B. napus.

Genetics of aliphatic glucosinolates. III. Side chain structure of aliphatic glucosinolates in Arabidopsis thaliana

“…5b). The presence of methylsuiphinylbutyl glucosinolate results from the inheritance of the Columbia allele at the GSL-ELONG locus described by Magrath et al (1994). Fifty-three of the RI lines had significant amounts of hydroxypropyl glucosinolate whereas the remaining 47 lines had no detectable amounts of this glucosinolate.…”

Genetics of aliphatic glucosinolates. II. Hydroxylation of alkenyl glucosinolates in Brassica napus

“…This linkage group is homoeologous to group 13 and is within the part of the B. napus genome which is homologous to the Brassica A genome. The relative positions of the two hydroxylation loci are analogous to the Gsl-elong-A and Gslelong-C loci (Magrath et at., 1994).…”

“…The C genome donor must have had functional alleles at this locus which resulted in at least 40 per cent hydroxylation of butenyl glucosinolates in leaves. Thus the leaf aliphatic glucosinolate content of the C genome donor must have comprised 60 per cent butenyl glucosinolates and 40 per cent hydroxybutenyl glucosinolates, the donor having null alleles at the Gsl-pro locus and functional alleles at the Gsl-alk locus, as explained previously (Magrath et a!., , 1994. Potential C genome taxa which have this profile will be described in a subsequent publication.…”

“…proportion of pentenyl glucosinolates (regulated by the Gsl-elong-A locus, Magrath et at., 1994), and that the Gsl-oh-A locus does not appear to be important in regulating hydroxylation. Thus both the Gsl-elong-A and Gsl-oh-A loci appear to be developmentally regulated with reduced expression of alleles at these loci in pod tissue.…”

“…Cobra and a synthetic B. napus line, as described previously (Magrath etal., 1993(Magrath etal., , 1994 hybrids, DNA extraction and restriction, Southern blotting and hybridization were as described previously (Magrath et at., 1994). Fifty recombinant lines from the second cross (including the 32 lines from which seed glucosinolates were analysed) were probed with 168 genomic probes which detected over 400 RFLP loci.…”