Up-regulated expression of desaturase genes of Mucor rouxii in response to low temperature associates with pre-existing cellular fatty acid constituents

Transcriptional response of desaturase genes to low temperature was investigated in the dimorphic fungus Mucor rouxii. The two morphological forms of M. rouxii, yeast-like and mycelial cells containing different fatty acid profiles were shifted from 30 to 10A degrees C. Both cultures exhibited significantly altered fatty acid composition, whose content in polyunsaturated fatty acids increased as consequence of the temperature shift and was accompanied by a reduction of C18:1 Delta(9) about 2 h after the temperature shift. These changes were particularly significant in phosphatidylcholine and phosphatidylethanolamine fractions. Moreover, the fatty acid profiles of monoacylglycerol and diacylglycerol were also modulated in response to the lower temperature of incubation. The changes of membrane lipids of M. rouxii were due to the cold-induced expression of Delta(9)-, Delta(12)- and Delta(6)-desaturase genes. Although the mRNA levels of the three desaturases were transiently induced by lowering the temperature, the pre-existing composition of fatty acid profiles of mycelial and yeast-like forms of M. rouxii may have lead to different expression profiles of desaturase genes that modified their membrane physical state under cold shock. While expression of Delta(12)-desaturase gene contributed mainly to cold acclimation of mycelia, Delta(9)-desaturase expression was the main transcript identified in the yeast-like culture after temperature shift.