Genetic analysis, expression and molecular characterization of BoGSL-ELONG, a major gene involved in the aliphatic glucosinolate pathway of Brassica species.

We cloned a major aliphatic glucosinolate (GSL) gene, BoGSL-ELONG in Brassica oleracea, using the Arabidopsis sequence database. We based our work on an Arabidopsis candidate gene forming part of a gene family coding for isopropyl malate synthetase-like enzymes (IPMS). This gene is presumably responsible for synthesis of GSL possessing side chains consisting of four carbons (4C). The similarity of the Brassica homolog IPMS-Bo from broccoli to its Arabidopsis counterpart IPMS-At was on the order of 78%, both sharing the same number of exons. A nonfunctional allele of the BoGSL-ELONG gene from white cauliflower, based on the absence of 4C GSL in this crop, displayed a 30-bp deletion, which allowed us to develop a codominant marker for 4C-GSL. Gene expression analysis based on RT-PCR revealed a splicing site mutation in the white cauliflower allele. This resulted in a longer transcript containing intron 3, which failed to excise. Perfect cosegregation was observed for broccoli and cauliflower alleles at the IPMS-Bo gene and 4C-GSL content, strongly indicating that this gene indeed corresponds to BoGSL-ELONG. Cloning of two other major genes, BoGSL-ALK and BoGSL-PRO, is underway. The availability of these genes and BoGSL-ELONG is essential for the manipulation of the aliphatic GSL profile of B. oleracea.