Abstract
BackgroundThe entomopathogenic fungus Metarhizium acridum has been used as an important biocontrol agent instead of insecticides for controlling crop pests throughout the world. However, its virulence varies with environmental factors, especially temperature. Neutral trehalase (Ntl) hydrolyzes trehalose, which plays a role in environmental stress response in many organisms, including M. acridum. Demonstration of a relationship between Ntl and thermotolerance or virulence may offer a new strategy for enhancing conidiospore thermotolerance of entomopathogenic fungi through genetic engineering.ResultsWe 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.ConclusionsNtl 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.
Highlights
The entomopathogenic fungus Metarhizium acridum has been used as an important biocontrol agent instead of insecticides for controlling crop pests throughout the world
We report here the construction of RNA interference (RNAi) and over-expression mutants of Neutral trehalase (Ntl) to investigate its role in thermotolerance and virulence of M. acridum
Our study shows that Ntl expression of M. acridum can be effectively enhanced or inhibited by over-expression or RNAi mutants, respectively, using a dual promoter system
Summary
The entomopathogenic fungus Metarhizium acridum has been used as an important biocontrol agent instead of insecticides for controlling crop pests throughout the world. Neutral trehalase (Ntl) hydrolyzes trehalose, which plays a role in environmental stress response in many organisms, including M. acridum. M. acridum isolates have been used as biocontrol agents for crop pests, including sugar cane grubs, termites, cockroaches, and rhinoceros beetles [1]. To genetically engineer more robust entomopathogenic fungi, we focused on the trehalose pathways involved in stress response. In many microorganisms and invertebrate animals, trehalose plays a role in environmental stress response [9,10] and is a known stress metabolite as its concentration increases during certain adverse environmental conditions, such as exposure to heat or toxic chemicals [11]. Based on the stress-protection properties of trehalose in vitro and the positive correlation between trehalose concentration and stress resistance in vivo, it is reasonable to expect that trehalose might function as a protective agent against stress [14,15]
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