The Effects Of Gene-Silencing Of Squlene Epoxidase And Phytoene Synthase On Biological Synthesis Of Triterpenes And Reactive Oxygen Species In Ganoderma Lucidum

Ganoderma lucidum, a traditional medicinal fungus used in China for a long term, has high value in nutrient and health care. Modern medical researches showed that the chemical composition triterpenes is one of the most important pharmacological ingredients of G lucidum. The content of triterpenes has been taken as an important measurement of the quality of G. lucidum. The content of triterpenes which is the secondary metabolites of Ganoderma lucidum is low in Ganoderma lucidum. It is an effectively solution to improve the medical value of Ganoderma lucidum by enhance the content of triterpenes.Triterpenes are biosynthesized via the mevalonate pathway. Mevalonate pathway is a major pathway in eukaryotic organisms. Farnesyl pyrophosphate in the pathway leads to the synthesis of triterpenes or carotenoids via different enzyme catalysis.Squalene epoxidase (EC 1.14.13.132, SE) is the key enzyme to catalyze the transformation of squalene to squalene 2,3-epoxide, which is a key step of triterpenes synthesis. Phytoene synthase (EC 2.5.132, PSY) is the key enzyme to catalyze two molecules of geranylgeranyl pyrophosphate condense into one molecular of phytoene which is the first metabolic product of carotenoid synthesis pathway.In order to clarify the functions of se and psy, we cloned the cDNA fragment of Gl-se and Gl-psy gene into gene-silencing vector pMi, and transform pMi-se and pMi-psy into Ganoderma lucidum applying the electroporation transformation method. The results show the content of triterpenes, squalene and lanosterol in sei transformats are lower significant than that in wild-type strain, while the content of carotene has increased.The expression levels of genes involved in triterpenes synthesis has decreased. The phenotypes psyi is opposite to sei.Sterol and carotenoid play an important role in clean the reactive oxygen species in organism. We check the reactive oxygen species in sei and psyi transformats. The results show that the reactive oxygen species in sei and psyi transformats have decreased. Then we check the resistances of these strains to oxidative stress. The result is that these strains have the similar resistances as wild-type strain. Thus we measure the activities of superoxide dismutase and catalase. The results indicate that the activities of catalase have increased in sei and psyi. The activities of superoxide dismutase have increased in psyi, while decreased in sei.