The adenylate cyclase gene MaAC is required for virulence and multi-stress tolerance of Metarhizium acridum.

Shuyang Liu,Yuxian Xia,Guoxiong Peng

doi:10.1186/1471-2180-12-163

Shuyang Liu, Yuxian Xia + Show 1 more

Open Access

https://doi.org/10.1186/1471-2180-12-163

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Abstract

BackgroundThe 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.ResultsCompared 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.ConclusionMaAC 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.

Highlights

The efficacy of entomopathogenic fungi in pest control is mainly affected by various adverse environmental factors, such as heat shock and Ultraviolet-B radiation (UV-B) radiation, and by responses of the host insect, such as oxidative stress, osmotic stress and fever
Our results showed that MaAC contributed to vegetative growth, virulence and tolerance to various adverse host insect and environmental factors
The results demonstrated that impairment in the virulence of the MaAC RNA interference (RNAi) mutant was caused by decreased vegetative growth and tolerance to adverse conditions encountered during host infection

Summary

Introduction

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. During the infection process of entomopathogenic fungi, germ tubes are produced after the fungal conidia attach regulatory processes involved in response to adverse factors from the host and environment is essential for the commercial development and improvement of fungi as biocontrol agents. Recent studies indicate that adenylate cyclase is required for normal vegetative growth, infection structure formation and virulence in phytopathogenic fungi. In the post-harvest necrotrophic fungus Botrytis cinerea, the deletion of the gene encoding adenylate cyclase reduced intracellular cAMP levels, causing delayed vegetative growth, lesion development and in planta sporulation [12]. Adenylate cyclase plays various roles in a number of fungi, the function of adenylate cyclase in entomopathogenic fungi has not been explored up to date

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