Analysis of KCS2 : a gene encoding a new condensing enzyme for the elongation of very long chain fatty acids in Arabidopsis thaliana

Condensing enzymes for very long chain fatty acid (VLCFA) synthesis catalyze the first of a series of four reactions that elongate the growing acyl chain by two carbons at a time. It has been shown that the activity of the condensing enzyme determines the amount and acyl chain length of the VLCFAs produced by a fatty acid elongation system. My research project focused on the characterization of KCS2, a new putative condensing enzyme of Arabidopsis thaliana. Computer database analyses showed that the KCS2 gene is located directly upstream of the FAE1 gene, the first condensing enzyme for the elongation of VLCFAs to be studied in Arabidopsis, suggesting a gene duplication phenomenon. Analysis of the expression pattern of KCS2 showed that the gene was primarily expressed in the anthers of Arabidopsis flowers. The ability of the condensing enzyme to elongate VLCFAs was determined by expressing it in yeast and in seeds of CB25, an Arabidopsis mutant defective in VLCFA elongation in the seed. In both systems, KCS2 was able to catalyze the elongation of VLCFAs. However, the accumulating products of fatty acid elongation carried out by the KCS2 condensing enzyme differed in the two organisms. Yeast accumulated preferentially saturated VLCFAs from C20:0 to C26:0, whereas Arabidopsis seeds accumulated primarily mono-unsaturated VLCFAs, C20:1 and C22:1. Finally, in an attempt to generate co-suppressed plants to determine the function of the KCS2 condensing enzyme, the KCS2 gene was transformed into Arabidopsis plants under the control of the CaMV35S promoter. No visible phenotype was obtained. However, some lines that were over-expressing the gene were able to synthesize more VLCFAs in the seed when compared to the wild type. In contrast, total wax load in stems of 35S-KCS2 over-expressors was not increased. Moreover, there was no correlation between the level of expression of the transgene and the amount of total wax produced. The specific function of the KCS2 condensing enzyme requires further study.Science, Faculty ofBotany, Department ofGraduat