Transcriptomic Analysis of Genes Associated with Cold-induced Storage Lipid Biosynthesis in Marine Haptophyte alga, Emiliania huxleyi

A few haptophyte algae in Isochrysidales are known to produce very long (C35-C40) straight-chain ketones called alkenones. The alkenone molecule possesses 2 to 4 trans-type unsaturation bonds. The number of unsaturation bond in a molecule of alkenone and whole amount of alkenones are known to be increased by cold signal although the biosynthesis and function of alkenones are not well understood yet. This study aimed to identify genes associated with cold-stimulated alkenone biosynthesis by transcriptomic analysis in cold-acclimated E. huxleyi. When cells were transferred from 25?C to 15?C, the unsaturation degree immediately increased although the amounts of both alkenone and fatty acids did not change. Almost all genes related to fatty acid biosynthesis and some genes assumed to be related to very long chain fatty acid synthesis were up-regulated. By factor analysis and qRT-PCR, we found four up-regulated genes related to lipid metabolism, namely fatty acid desaturase, acetylcholinesterase, choline transporter-like protein and phospholipid scramblase. Sequence alignment showed that this fatty acid desaturase is unique and no homologous proteins in database, suggesting to be specific to E. huxleyi. This putative fatty acid desaturase may function as alkenone desaturase.