Effects of low temperature and exogenous unsaturated fatty acids on fatty acid desaturase gene expression of Mortierella alpina ATCC 16266

Abstract:

Abstract:［Objective］In order to investigate the regulatory mechanisms of Mortierella alpina desaturase genes by low temperature and exogenous unsaturated fatty acids (UFAs) at the transcriptional level．［Methods］We performed timecourse studies of fatty acid desaturase gene expression by real-time PCR and determined fatty acid desaturase gene promoter activity using promoter-reporter constructs． ［Results］Relative expression results in real-time PCR showed that the mRNA levels of three fatty acid desaturase genes (Fad6，Fad12 and Fad3) were rapidly and transiently enhanced after 1 h of shifting to low temperature，in contrast，high concentration of exogenous oleic acid (OA) which was a monounsaturated fatty acid containing a D9 double bond suppressed the transcription of these genes and the transcriptional response appeared to be rapid and transient． Also，there was no absolute correlation between mRNA abundance and production of corresponding fatty acids． The pFAD6 promoter activity was induced by low temperature in a time-dependent manner and reduced in a dose- and time-dependent manner by addition of UFAs to the media，and α-linolenic acid (ALA) containing three double bonds appeared to have a more effective inhibition than linoleic acid (LA) and OA．［Conclusion］These results indicate that there may be post-transcriptional control and other modes of regulation of UFAs synthesis in M． alpina when facing different stimuli such as low temperature and exogenous unsaturated fatty acids besides the regulation in the transcription of fatty acid desaturase genes at the initial stage． Also，there may be an unknown endproduct (changes in fatty acid compositions) feedback regulation in the transcription of fatty acid desaturase genes to maintain cellular UFAs' homeostasis． In a word，we assessed mechanisms of transcriptional regulation in M． alpina fatty acid desaturase gene expression for the first time and we wish to make it possible to obtain a better understanding of the mechanisms and get some theoretical knowledge to offer some guidance to the industrial production of UFAs by transgenic technology and microbial fermentation technology．

Key words:Keywords: low temperature，unsaturated fatty acids，fatty acid desaturase，real-time PCR，promoter