Functional Analysis Of Mapkinase MAPK4 And Transcription Factor SWI6 In Ganoderma Lucidum

Ganoderma lucidum is a traditional medicinal mushroom with highly medical values, and widely used in China, Japan, Korea and Southeast Asia. G. lucidum have been reported to possess numerous biological activities including anti-aging activity, improving immunity effects, lowering blood pressure effects, increasing anticancer activity and so on. Ganoderic acids (GAs), which is one of the secondary metabolites in G. lucidum, are considered as the main active ingredient. Previous studies found that the yield of GAs is significantly improved by changing environmental conditions. However, due to the physiological characteristics of G. lucidum and lacking genetic manipulation system, the mechanism of exogenous environmental factors induces GAs synthesis is unknown. Characterize the regulation of GA biosynthetic would be valuable and might be helpful for enhancing GAs production in the future. Therefore, it is necessary and important to analyze the regulatory mechanism of GAs biosynthesis by effective genetic methods. This study will helpful in promoting G. lucidum as a model of medical fungus in the future.Mitogen-activated protein kinase (MAPK) is one of the kinases in fungi. Mitogen-activated protein kinase cascade (MAPK cascade) and transcription factors are activated immediately after stimulate. As a result, related genes are expressed in response to external environmental stimuli. The transcription factors are downstream of MAPK. As a key factor on cell wall integrity (CWI) signal pathway, SLT2 MAPK plays an important role in the regulation of external stress, hyphal growth, development, secondary metabolism and so on. In this study, function of mapk4 gene and transcription factor swi6 gene are analyzed by RNA interference.In this research, mapk4 gene which is Slt2 MAPK homologous gene of Saccharomyces cerevisiae was found according to the genome database of G. lucidum. It is identified by analysis of its functional domains, phylogenetic and subcellular localization. RNA interference (RNAi) was used to examine the function of the mapk4 gene. The result indicated a central role for this gene in hyphal growth, cell wall biosynthesis, ganoderic acid biosynthesis, ROS accumulation, cellulase and laccase activity. Additionally, the mapk4 gene is required for fruiting body development, H2O2 resistance, acetic acid and cell wall-stressing agents’ resistance.Additionally, RNAi was also used to examine the function of the swi6 gene. The research indicated a key role for this gene in hyphal growth and ganoderic acid biosynthesis. Additionally, the swi6 gene is required for SDS resistance.In summary, this study found a significant role for mapk4 gene in hyphal growth, development and secondary metabolism. It’s similar to other filamentous fungi. Additionally, it was found that transcription factor swi6 gene involved in the regulation of hyphal growth and secondary metabolism. Summary, the two key factors of CWI signaling pathway show the similar physiological functions.