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BMC Microbiol. 2012; 12: 163.
Published online Aug 1, 2012. doi:  10.1186/1471-2180-12-163
PMCID: PMC3438079
The adenylate cyclase gene MaAC is required for virulence and multi-stress tolerance of Metarhizium acridum
Shuyang Liu,#1,2,3 Guoxiong Peng,#1,2,3 and Yuxian Xiacorresponding author1,2,3
1Genetic Engineering Research Center, College of Bioengineering, Chongqing University, Chongqing, 400030, P. R. China
2Chongqing Engineering Research Center for Fungal Insecticides, Chongqing, 400030, P. R. China
3Key Lab of Functional Gene and Regulation Technologies under Chongqing Municipal Education Commission, Chongqing, 400030, P. R. China
corresponding authorCorresponding author.
#Contributed equally.
Shuyang Liu: chris-yy33/at/163.com; Guoxiong Peng: gxpeng/at/cqu.edu.cn; Yuxian Xia: yuxianxia/at/cqu.edu.cn
Received February 14, 2012; Accepted July 26, 2012.
Abstract
Background
The efficacy of entomopathogenic fungi in pest control is mainly affected by various adverse environmental factors, such as heat shock and UV-B radiation, and by responses of the host insect, such as oxidative stress, osmotic stress and fever. In this study, an adenylate cyclase gene (MaAC) was cloned from the locust-specific entomopathogenic fungus, Metarhizium acridum, which is homologous to various fungal adenylate cyclase genes. RNA silencing was adapted to analyze the role of MaAC in virulence and tolerance to adverse environmental and host insect factors.
Results
Compared with the wild type, the vegetative growth of the RNAi mutant was decreased in PD (potato dextrose medium), Czapek-dox and PDA plates, respectively, demonstrating that MaAC affected vegetative growth. The cAMP levels were also reduced in PD liquid culture, and exogenous cAMP restored the growth of RNAi mutants. These findings suggested that MaAC is involved in cAMP synthesis. The knockdown of MaAC by RNAi led to a reduction in virulence after injection or topical inoculation. Furthermore, the RNAi mutant grew much slower than the wild type in the haemolymph of locust in vitro and in vivo, thus demonstrating that MaAC affects the virulence of M. acridum via fungal growth inside the host locust. A plate assay indicated that the tolerances of the MaAC RNAi mutant under oxidative stress, osmotic stress, heat shock and UV-B radiation was decreased compared with the wild type.
Conclusion
MaAC is required for virulence and tolerance to oxidative stress, osmotic stress, heat shock and UV-B radiation. MaAC affects fungal virulence via vegetative growth inside the insect and tolerance against oxidative stress, osmotic stress and locust fever.
Keywords: Biocontrol agents, Entomopathogenic fungi, Conidia, Virulence, Environmental stress
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