Regulation and accumulation of secondary metabolites in plant-fungus symbiotic system

Plants have evolved adaptive strategies to mutualistic microbes penetration for both mycorrhizal fungi and endophytic fungi. Subsequently, an array of host plant defense responses and signal transduction is generated. A group of secondary metabolites are accumulated inducibly or enhanced constitutively in plant tissues during the process. Symbiotic fungi usually perform compatible and friendly interactions with host plants, which contribute to growth promotion and secondary metabolites accumulation simultaneously, such as alkaloids and terpenoid with pharmacological characteristics. Especially, some secondary metabolites derived from root exudation act as signal molecules, which induce the spore germination and hypha branching in mycorrhizal fungi. However, the precise mechanisms in some cases remain unclear so far and need to be further investigated. Above exciting and interesting results shed light on our understanding of the mystery of fungal elicitation of secondary metabolites accumulation in plant kingdom. Therefore a deeper insight in mutualistic symbiosis is of great importance for biological applications: (1) the plant/microbial co-culture system in vitro may be perfectly useful to guide the cultivation of medicinal plants for obtaining high level of bioactive compounds; (2) manipulating plant released signal molecules and isoprenoid metabolism will be effective to optimize and improve the function of mycorrhizae in forestry, agriculture and horticulture.