Biocontrol Mechanism Of The Bacterial Biocontrol Agent PC60 Against Fusarium Head Blight Of Wheat

The filamentous fungus Fusarium graminearum is an important plant pathogen causing Fusarium head blight(FHB),which leads to a devastating disease of cereal crop.Currently,the application of systemic fungicides has become one of the primary tools for controlling FHB.The overuse of chemical compounds leads to fungicide resistance.In addition,some fungicides could induce the production of mycotoxins in the infected cereals,e.g.deoxynivalenol(DON)and zearalenone(ZEN),which pose a serious threat to the food safety and human health.Therefore,a biocontrol strategy may be important for management of FHB.In this study,a novel biocontrol agent PC60 isolated from wheat was identified based on its excellent antagonistic activity against F.graminearum in vitro.This strain was subsequently characterized as Pseudomonas chlororaphis.According to the genomic sequence,PC60 should be capable of generating phenazine compounds including phenazine-1-carboxamide(PCN)and phenazine-1-carboxylic acid(PCA).The major antifungal metabolite produced by PC60 was further extracted and identified as PCN that showed a strong inhibitory activity against F.graminearum.The phzA-H is a core PCN biosynthesis gene cluster in PC60.The phzA-H knockout mutant showed a poor inhibitory activity against F.graminearum.Taken together,these results indicate that PCN is a major antifungal compound produced by the PC60.In order to explore the mechanisms of PCN against fungi,we identified yeast mutants that showed changes in sensitivity to PCN by a library screening strategy.Our results showed that PCN could interfere with four pathways including cell cycle、oxidative stress,cellular morphogenesis,and multidrug transport in the yeast.However,these homologous genes were not involved in the susceptible of F.graminearum to PCN.We further screened a partial F.graminearum mutant library containing more than 1000 mutants established by our lab.Fortunately,a mutant named AFgPCN showed increased sensitivity dramatically to PCN.Unexpected,the homolog of FgPCN is not involved in sensitivity of yeast to PCN.These results indicated that PCN has different mechanism against F.graminearum from yeast.In conclusion,the results of current study provide useful information for development of the biocontrol agent PC60 against FHB.