Relationship Between Oxidative Tolerance And Polysacharride In Aerial Conidia Of The Entomopathogenic Fungi And The Functional Analysis Of BbAtf1in Beauveria Bassiana

Relationship between oxidative tolerance and polysacharride in aerial conidia of the entomopathogenic fungi. Entomopathogenic hyphomycete has long been widely applied in biocontrol of insect pests due to easy production, formulation and environmental safety. This study was to illustrate the relationship between the oxidative tolerance and the polysaccharide contents in aerial conidia of Beauveria bassiana and Isaria fumosoroseus. Survival indices of11isolates were separately assessed as a ratio of the viability of conidia exposed to10-min stress with H2O2over that of unstressed conidia and fitted well to a survival model (r2>0.95). For a given isolate, the fitted model generated an LD50, the concentration for50%viability loss under the stress. As a result, I. fumosoroseus was more tolerant to oxidative stress than B. bassiana. The LD50for B. bassiana and I. fumosoroseus was correlated well to the conidial polysaccharide content of the respective strain. The conidial contents of B. bassiana could be modified by changing the concentration and type of sugar in media. However, the survival indices of isolate were still correlated well to the polysaccharide contents from conidia produced on glucose-, sucrose-, or starch-based media. The relationship between conidial polysaccharide content and oxidative tolerance suggested an alternative strategy to improve fungal biocontrol agents with more environmental stability.Functional analyses of BbAtfl in B.bassina. Gene Atfl, a core cAMP responsive element binding protein (CREB), is an important downstream target of the mitogen-activated protein kinase (MAPK) pathway, and plays a great role in diverse cellular processes, such as cellular metabolism, cellular structure, signal transduction and synaptic transmission. The roles of BbAtfl in regulating the growth, stress tolerance and virulence of B. bassiana were probed by generating ΔBbAtfl and ΔBbAtfl/BbAtfl mutants through the homologous recombination and random insertion methods mediated by Agrobacterium tumefaciens AGL-1. First, ΔBbAtfl displayed39.4%reduction in conidial thermotolence (LT50:49.96min versus82.5min) and32.6%decrease in UV-B resistance (LD50:0.31J/cm2versus0.46J/cm2). Second, thcΔBbAtfl conidia became66.7%less tolerance to the oxidants H2O2than the control strains (EC50:0.3mM versus0.1mM). Third, ΔBbAtfl showed a decrease level of16.5%in virulence compared with the control strains to Galleria mellonella larvae via the topical infection. Last, qRT-PCR data showed the transcriptional levels of the two catalases (sod3and cat4) were greatly repressed in ΔBbAtfl under the H2O2stress. In conclusion, our study indicates BbAtfl is an important transcription factor in B.bassiana, particularly in regulating the oxidative stress response of B. bassiana, which may supply a new target in explaining the molecular mechanism involved in virulence and improving the strains of the fungal entomopathogen.