Study On Fatty Acid Desaturases And Fatty Acids Profile In Chlamydomonas Sp. ICE-L

Unsaturated fatty acids (UFA) have many important physiological functions inorganism. They are necessary for membrane structure and function. polyunsaturatedfatty acids (PUFAs) were dominant compositions, accounting for more than75%totalFA in Chlamydomonas sp. ICE-L, which is a major biomass producer in Antarctica.The major FAs biosynthesized pathways in microalgae are not the same. There aretwo interconnected pathways of FA biosynthesis: the “eukaryotic” pathway is locatedin the endoplasmic reticulum and the “prokaryotic” pathway is located in thechloroplast. Two types of fatty acid desaturases (FADs), which function at theendoplasmic reticulum (ER) and the chloroplast respectively, are responsible for FAdesaturation. FADs are enzymes that introduce double bonds into the hydrocarbonchains of fatty acids to produce monounsaturated fatty acids (MUFAs) and PUFAs.The limiting enzyme in the conversion of saturated fatty acids (SFAs) to UFAs,Δ7/Δ9FAD, inserts the first double bond into SFAs. Δ12FAD, called ω6desaturase,converts C16:1or C18:1to C16:2or C18:2by inserting a double bond at the ω6position, whereas ω3desaturases insert a double bond at the ω3position and Δ4, Δ5,Δ6and Δ8FAD are considered to be responsible for the production ofeicosapentaenoic acid (EPA).This paper was carried out by the following steps: First, Δ9CiFAD, Δ12CiFAD,Δ6CiFAD, ω3CiFAD1and ω3CiFAD2were cloned and analysised and the function ofΔ12CiFAD gene was studied from Chlamydomonas sp. ICE-L. Sequence alignmentshowed that these genes are homologous to known FADs with conserved histidinemotifs. The expression of Δ12CiFAD in Synechococcus6803and Saccharomyces cerevisiaethe was performed for analysis of its bioactivities subsequently. Resultsindicated that recombinant Synechococcus6803with Δ12CiFAD fromChlamydomonas sp. ICE-L could accumulate C18:2, while recombinant S.cerevisiaethe with Δ12CiFAD could not accumulate C18:2and other new FA.Some environmental factors (such as temperature, salinity, etc.) can impact theexpression and activity of desaturases, which is achieved by some of the molecularmechanisms. The cells can quickly adapt to the changes in the environment bychanging in the composition of fatty acids. Results showed that the expressions ofΔ9CiFAD, ω3CiFAD1and ω3CiFAD2were apparently up-regulated at0°C, however,the up-regulation of Δ6CiFAD intensified with rising temperature. Meanwhile,analysis of the FA compositions showed that PUFAs were significantly increased at0and5°C, which may be attributed to higher proportions of C18:3and C20:3.Moreover, PUFAs were significantly decreased at15°C whereas SFAs weresignificantly increased. Under salt stress, the expression of Δ9CiFAD increasedrapidly while Δ12CiFAD, ω3CiFAD2and Δ6CiFAD showed a delayed elevation inresponse to altered salt stress. Under96‰and128‰NaCl stress, the content ofC20:5almost approached that of C18:3. In contrast, low salinity enhanced thedominance of C18:3at the expense of C20:3and C20:5.To the best of our knowledge, this is the first time the five FADs have beenanalyzed together in Chlamydomonas sp. ICE-L. Efforts were made to determine theFA desaturation metabolic pathway of the microalga. The study of FADs fromChlamydomonas sp. ICE-L may show that temperature and salinity can impact theexpression and activity of desaturases, which enable a more comprehensiveunderstanding the functions of FADs and FA compositions in response to stress.