Genetically altering the expression of neutral trehalase gene affects conidiospore thermotolerance of the entomopathogenic fungus Metarhizium acridum

We selected four Ntl over-expression and four Ntl RNA interference (RNAi) transformations in which Ntl expression is different. Compared to the wild-type, Ntl mRNA expression was reduced to 35-66% in the RNAi mutants and increased by 2.5-3.5-fold in the over-expression mutants. The RNAi conidiospores exhibited less trehalase activity, accumulated more trehalose, and were much more tolerant of heat stress than the wild-type. The opposite effects were found in conidiospores of over-expression mutants compared to RNAi mutants. Furthermore, virulence was not altered in the two types of mutants compared to the wild type.Ntl controlled trehalose accumulation in M. acridum by degrading trehalose, and thus affected conidiospore thermotolerance. These results offer a new strategy for enhancing conidiospore thermotolerance of entomopathogenic fungi without affecting virulence.Metarhizium acridum is a haploid entomopathogenic fungus (Hypocreales: Clavicipitaceae). M. acridum isolates have been used as biocontrol agents for crop pests, including sugar cane grubs, termites, cockroaches, and rhinoceros beetles [1]. M. acridum was commercialized and used for locust control in Australia, West Africa [2], and China [3].Insecticide resistance, pest resurgence, and concerns over environmental impact have made the search for alternative means of biological pest control more urgent. Unfortunately, large-scale use of fungal biocontrol agents is partially limited by the failure of conidia to retain virulence during long-term storage, transportation, and use under stressful conditions, such as high temperature, low humidity, and sunlight exposure [4-6]. Manipulation of culture conditions could optimize the concentration of spore polyols and sugars, including trehalose, and consequently increase tolerance to low relative humidity [7,8]. However, genetic manipulations of these polyols and sugars to enhance environmental tolerance have not been explored in entomopathogenic fungi.To geneticall