Molecular Mechanism of Overcoming Host Resistance by the Target of Rapamycin Gene in Leptographium qinlingensis
Leptographium qinlingensisis a fungal symbiont of the Chinese white pine beetle (Dendroctonus armandi) and a pathogen of the Chinese white pine (Pinus armandii) that must overcome the terpenoid oleoresin defenses of host trees to invade and colonize.L. qinlingensisresponds to monoterpene flow with abundant mechanisms that include the decomposing and use of these compounds as a nitrogen source. Target of Rapamycin (TOR) is an evolutionarily conserved protein kinase that plays a central role in both plants and animals through integration of nutrients, energies, hormones, growth factors and environmental inputs to control proliferation, growth and metabolism in diverse multicellular organisms. In this study, in order to explore the relationship betweenTORgene and carbon sources, nitrogen sources, host nutrients and host volatiles (monoterpenoids) inL. qinlingensis, we set up eight carbon source treatments, ten nitrogen source treatments, two host nutrients and six monoterpenoids (5%, 10% and 20%) treatments, and prepared different media conditions. By measuring the biomass and growth rate of mycelium, the results revealed that, on the whole, the response ofL. qinlingensisto nitrogen sources was better than carbon sources, and the fungus grew well in maltose (carbon source), (NH4)2C2O4(inorganic nitrogen source), asparagine (organic nitrogen source) andP. armandii(host nutrient) versus other treatments. Then, by analyzing the relationship betweenTORexpression and different nutrients, the data showed that: (i)TORexpression exhibited negative regulation in response to carbon sources and host nutrition. (ii) The treatments of nitrogen sources and terpenoids had positively regulatory effects onTORgene; moreover, the fungus was most sensitive to β-pinene and 3-carene. In conclusion, our findings reveal thatTORinL. qinlingensisplays a key role in the utilization of host volatiles as nutrient intake, overcoming the physical and chemical host resistances and successful colonization.Keywords:Leptographium qinlingensis;Target of Rapamycingene;carbon sources;nitrogen sources;host nutrition;terpenoids
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