SSADH基因调控对高山被孢霉脂质合成的影响

Effects of SSADH gene regulation on lipid synthesis of the oleaginous fungus Mortierella alpina

高山被孢霉合成油脂能力很强,可合成多种n-3和n-6系列多不饱和脂肪酸(PUFAs)。γ-氨基丁酸(GABA)代谢途径是由谷氨酸经过一系列反应转化至琥珀酸并产生NADPH的过程,同时可为产油真菌生长提供碳源和氮源。通过构建γ-氨基丁酸途径中琥珀酸半醛脱氢酶(SSADH)基因RNA干扰菌株(MA-i SSADH),对MA-i SSADH中的脂肪酸组成、NADPH水平及相关基因转录水平进行分析,研究SSADH与高山被孢霉脂质合成关系。与原养型高山被孢霉(M.alpina)相比,MA-i SSADH中SSADH基因转录水平显著下调,同时脂肪酸总含量下降了20.9%,C18∶1相对含量提高了73.5%,表明SSADH在高山被孢霉脂质合成中起重要作用。尽管MAi SSADH中NADPH绝对含量没有发生显著性变化,但NADPH合成相关基因如苹果酸酶(ME)、葡萄糖-6-磷酸脱氢酶(G6PD)、6-磷酸葡萄糖酸脱氢酶(6PGD)、异柠檬酸脱氢酶(IDH)、亚甲基四氢叶酸脱酸酶(MTHFD)基因转录水平均发生了显著变化,表明SSADH对NADPH合成途径产生了重要调控,这可能是其影响脂质合成的原因之一。

M. alpina has strong ability to synthesize lipid and can synthesize a variety of n-3 and n-6 series polyunsaturated fatty acids（ PUFAs）. γ-Aminobutyric acid（ GABA） metabolism pathway is a process in which glutamate is converted to succinic acid through a series of reactions and produces NADPH,and can provide nitrogen source and carbon source for the growth of fungi for lipid synthesis. By constructing RNA recombinant strain（ MA-iS SADH） of succinic semialdehyde dehydrogenase（ SSADH）gene in GABA metabolism pathway,the fatty acid composition of MA-iS SADH,the content of NADPH and the transcriptional level of related genes generating NADPH were analyzed to investigate the role of SSADH in M. alpina during lipid synthesis. Compared with M. alpina,the transcriptional level of SSADH decreased significantly and the content of total fatty acid decreased by 20. 9%,while the relative content of C18∶ 1 increased by 73. 5% in MA-iS SADH. It indicated that the SSADH played an important role in the lipid synthesis of M. alpina. Although there was no obvious change in content of NADPH,the transcriptional level of related genes generating NADPH such as malic acid（ ME）,glucose-6-phos-phate dehydrogenase（ G6 PD）,6-phosphogluconate dehydrogenase（ 6 PGD）, isocitrate hydrogenase（ IDH） and methylenetetrahydrofolate dehydrogenase（ MTHFD） changed significantly,which showed that SSADH regulated the source of NADPH required for the lipogenesis,and thus played an important role in lipid synthesis of M. alpina.