Cloning and functional characterization of a Δ12 fatty acid desaturase gene from the basidiomycete Lentinula edodes

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Abstract
In the basidiomycete Lentinula edodes, a famous edible mushroom (shiitake), the fatty acyl composition of total lipids has previously been shown to change during cell differentiation. In the present study, we succeeded in cloning a gene for a Δ12 fatty acid desaturase from L. edodes. The ORF of this gene (named Le-FAD2) consists of 1308 bp and codes for 435 amino acids. The deduced Le-FAD2 protein shows 40–45% identity to Δ12 fatty acid desaturases from other fungi, and the three histidine clusters typical of the catalytic domain of such enzymes are conserved. Expression of the Le-FAD2 gene in the budding yeast Saccharomyces cerevisiae indicated that its product was able to synthesize linoleic acid (C18:2). Analysis of Le-FAD2 expression in L. edodes revealed that levels of transcription were higher in fruiting body primordia and in mature fruiting bodies, the two differentiated tissues, than in mycelium, and reduction of the growth temperature from 25 to 18°C had no effect on the level of the Le-FAD2 transcript. Thus, although Le-FAD2 expression is correlated with the alteration in the complement of unsaturated fatty acids (UFAs) observed during fruiting body formation, the gene does not respond to a downshift in temperature to 18°C.