Microalgae lipids and oils are potential candidates for renewable biodiesel. Many microalgae species accumulate a substantial amount of lipids and oils under environmental stresses. However, low growth rate under these adverse conditions account for the decrease in overall biomass productivity which directly influence the oil yield. This study was undertaken to investigate the effect of exogenously added auxin (indole-3-acetic acid; IAA) on the oil content, fatty acid compositions, and the expression of fatty acid biosynthetic genes in Chlorella vulgaris (UMT-M1). Auxin has been shown to regulate growth and metabolite production of several microalgae. Results showed that oil accumulation was highest on days after treatment (DAT)-2 with enriched levels of palmitic (C16:0) and stearic (C18:0) acids, while the linoleic (C18:2) and α-linolenic (C18:3n3) acids levels were markedly reduced by IAA. The elevated levels of saturated fatty acids (C16:0 and C18:0) were consistent with high expression of the β-ketoacyl ACP synthase I (KAS I) gene, while low expression of omega-6 fatty acid desaturase (ω-6 FAD) gene was consistent with low production of C18:2. However, the increment of stearoyl-ACP desaturase (SAD) gene expression upon IAA induction did not coincide with oleic acid (C18:1) production. The expression of omega-3 fatty acid desaturase (ω-3 FAD) gene showed a positive correlation with the synthesis of PUFA and C18:3n3.
As the world population grows, the demand for food increases. Although vegetable oils provide an affordable and rich source of energy, the supply of vegetable oils available for human consumption is limited by the "fuel vs food" debate. To increase the nutritional value of vegetable oil, metabolic engineering may be used to produce oil crops of desirable fatty acid composition. We have isolated and characterized β-ketoacyl ACP-synthase II (KASII) cDNA from a high-oleic acid palm, Jessenia bataua. Jessenia KASII (JbKASII) encodes a 488-amino acid polypeptide that possesses conserved domains that are necessary for condensing activities. When overexpressed in E. coli, recombinant His-tagged JbKASII was insoluble and non-functional. However, Arabidopsis plants expressing GFP-JbKASII fusions had elevated levels of arachidic acid (C20:0) and erucic acid (C22:1) at the expense of stearic acid (C18:0) and oleic acid (C18:1). Furthermore, JbKASII failed to complement the Arabidopsis KASII mutant, fab1-2. This suggests that the substrate specificity of JbKASII is similar to that of ketoacyl-CoA synthase (KCS), which preferentially elongates stearic and oleic acids, and not palmitic acid. Our results suggest that the KCS-like JbKASII may elongate C18:0 and C18:1 to yield C20:0 and C22:1, respectively. JbKASII may, therefore, be an interesting candidate gene for promoting the production of very long chain fatty acids in transgenic oil crops.