Cloning and Gene Expression of the 3-Ketoacyl-CoA Reductase in B. napus Seeds

Abstract

The membrane-bound acyl-CoA elongases are responsible for the synthesis of Very Long Chain Fatty Acids (VLCFA) which are the primer of wax constituents and are the major fatty acid is some seeds. VLCFA result from elongation of oleoyl-CoA by malonyl-CoA through four successive reactions: condensation (CE), keto-acyl-CoA reduction (KCR), dehydratation (DH) and enoyl-CoA reduction (ER) (Domergue et al., 1998). The elongation mechanism has been extensively studied but the organization of the acyl-CoA elongase in the membrane remains unclear although genes encoding 3-ketoacyl-CoA synthases have been cloned. Recent advances in the knowledge of the other proteins of the elongation complex from the leaf have been made. Firstly, the characterization of maize g18 cDNA as a ketoacyl-CoA redutase of the acyl-CoA elongase involved in wax biosynthesis was reported (Xu et al., 1997, 2002) and secondly an A.thaliana clone was also characterized as a ketoacyl-CoA redutase by the complementation of a yeast mutant (Beaudoin et al., 2002). In high erucic acid rapeseed (HEAR), the knowledge of the elongation complex which synthesizes erucic acid is incomplete despite its biotechnological importance. In this paper, we describe the isolation of two cDNAs encoding a 3-ketoacyl-CoA synthase using a B.napus probe made from A.thaliana Glossy 8 cDNA sequence. The analysis of Bn KCR 1 and Bn KCR 18 amino acids sequences and the expression of the corresponding mRNA during seed development are also reported.