Functional characterization of beta-ketoacyl-CoA synthase genes from Brassica napus L.

Seed-specifically expressed beta -ketoacyl-CoA synthase genes of Brassica n apus (Bn-FAE1.1 genes) were cloned from two cultivars, namely Askari, a hig h-erucic-acid type, and Drakkar, a low-erucic-acid type. The genes from the two cultivars were found to be nearly identical. They encode proteins of 5 07 amino acids, the sequences of which differ only at position 282. The Bn- FAE1.1 gene of Askari, unlike that of Drakkar, was functionally expressed i n yeast cells suggesting that the single amino acid exchange effects the lo w erucic acid phenotype at the E1 gene locus. In yeast cells the beta -keto acyl-CoA synthase of Askari elongated not only oleoyl but also palmitoleoyl groups as well as saturated acyl groups in such a way that monounsaturated acyl groups of 22 carbons and saturated ones of 26 carbons were formed as main products. A reporter gene fused to the promoter region of the Bn-FAE1. 1 gene from Askari showed seed-specific expression in transgenic rapeseed p lants. Over-expression of the coding region of the Askari gene in developin g seeds of transgenic Drakkar plants resulted in a significant increase in the levels of eicosenoic acid and erucic acid esterified in the seed oil. O n the other hand, in transgenic high-erucic-acid rapeseed plants the increa se in erucic acid level was at most 60% although the chimeric Bn-FAE1.1 gen e was co-expressed with an erucoyl-CoA-specific lysophosphatidate acyltrans ferase gene enabling trierucoyl glycerol to accumulate in the seed oil.