A novel omega-3 fatty acid desaturase involved in acclimation processes of polar condition from Antarctic ice algae Chlamydomonas sp. ICE-L

The ability of Antarctic ice algae, Chlamydomonas sp. ICE-L, to survive and proliferate at low temperature and high salinity implies that they have overcome key barriers inherent in Antarctic environments. A full-length complementary DNA (cDNA) sequence of omega-3 fatty acid desaturase, designated CiFAD3, was isolated via reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends methods. The full-length of CiFAD3 cDNA contained an open reading frame of 1,302 bp with 5′-terminal untranslated region (UTR) of 36 bp and 3′-terminal UTR of 507 bp encoding a fatty acid desaturase protein of 434 amino acids. Sequence alignment and phylogenetic analysis showed that the gene was homologous to known chloroplastic omega-3 fatty acid desaturase. Meanwhile, CiFAD3 sequence showed typical features of membrane-bound desaturase such as three conserved histidine boxes along with four membrane spanning regions that were universally present among plant desaturases. Under different stress conditions, messenger RNA (mRNA) expression levels of CiFAD3 were measured by quantitative RT-PCR. The results showed that both temperature and salinity could motivate the upregulation of CiFAD3 expression. The mRNA accumulation of CiFAD3 increased 2.6-fold at 0°C and 1.8-fold at 12°C compared to the algae at 6°C. Similarly, mRNA expression levels of CiFAD3 increased 3.8-fold after 62‰ NaCl treatment for 2 h. However, CiFAD3 mRNA expression levels were partially decreased after UV radiation. These data suggest that CiFAD3 is the enzyme responsible for the omega-3 fatty acid desaturation involved in ice algae Chlamydomonas sp. ICE-L acclimatizing to cold temperature and high salinity in Antarctic environment.