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  • Review Article
  • Published:

Hypovirulence: Mycoviruses at the fungal–plant interface

Nature Reviews Microbiology volume 3, pages 632–642 (2005)Cite this article

Key Points

  • This review provides an overview of the mycoviruses that are associated with the attenuation of fungal pathogenesis that is known as hypovirulence.

  • The taxonomy and genome organization of hypoviruses are outlined. These viruses are in the taxonomic family Hypoviridae, which cause hypovirulence of the chestnut blight fungus Cryphonectria parasitica.

  • The development of hypovirus reverse genetics systems is described.

  • Hypovirus diversity has been exploited to identify symptom determinants and modulate fungal–plant pathogenic interactions.

  • Potentially, mycoviruses could be used to explore the origins, evolution and functions of RNA silencing in fungi. These viruses could also be used to probe the signal transduction pathways that underpin fungal pathogenesis.

  • Hypovirus-mediated modulation of the host transcriptome has been analysed using microarrays, which has confirmed hypovirus-mediated alterations of host functions including G-protein signalling, and has revealed a link between mitochondrial and viral hypovirulence.

  • Finally, the prospects for engineering hypoviruses to improve their suitability for biological control of fungal diseases of plants are discussed.

Abstract

Whereas most mycoviruses lead 'secret lives', some reduce the ability of their fungal hosts to cause disease in plants. This property, known as hypovirulence, has attracted attention owing to the importance of fungal diseases in agriculture and the limited strategies that are available for the control of these diseases. Using one pathogen to control another is appealing, both intellectually and ecologically. The recent development of an infectious cDNA-based reverse genetics system for members of the Hypoviridae mycovirus family has enabled the analysis of basic aspects of this fascinating virus–fungus–plant interaction, including virus–host interactions, the mechanisms underlying fungal pathogenesis, fungal signalling pathways and the evolution of RNA silencing. Such systems also provide a means for engineering mycoviruses for enhanced biocontrol potential.

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Figure 1: Taxonomic families and primary modes of hypovirulence-associated mycovirus transmission.
Figure 2: Genetic organization and basic expression strategy for prototypic hypovirus CHV1-EP713.
Figure 3: Hypovirus reverse genetics.
Figure 4: Effect of hypovirus infection on Cryphonectria parasitica colony and canker morphologies.
Figure 5: Hypovirus symptom determinants and modulation of fungal–plant interactions.

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Acknowledgements

I am grateful to T. Allen, F. Deng, L. Geletka & G. Segers for suggestions and corrections. This work was supported in part by a Public Health Service grant.

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  1. Center for Biosystems Research, 5115 Plant Sciences Building, University of Maryland Biotechnology Institute, College Park, Maryland, 20742, USA

    Donald L. Nuss

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DATABASES

Entrez Gene

Entrez Gene

CHV1-EP713

Hv145SV

Hv190SV

FURTHER INFORMATION

Donald L. Nuss' homepage

COGEME

Glossary

BIOCONTROL

The use of one species of organism to eliminate or control another through a biological mechanism.

ANASTOMOSIS

Fusion of somatic hyphae followed by exchange of cellular contents.

TRANSGENIC HYPOVIRULENCE

Virulence-attenuated fungal strains that contain a chromosomally-integrated, infectious hypovirus cDNA.

CONIDIA

Asexual spores.

cDNA MICROARRAY

A collection of cDNA clones spotted on a support media such as a micoscope slide, in a high-density ordered array that is suitable for hybridization to appropriate nucleic-acid probes.

EXPRESSED SEQUENCE TAG

(EST). A cloned cDNA copy of the mRNAs isolated from an organism. The combined collection (library) of EST clones represents the transcribed genes in that sample.

VEGETATIVE INCOMPATIBILITY

A genetic system that controls the ability of two fungal strains to anastomose. In C. parasitica, this system consists of at least six genetic loci, each containing two alleles.

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Nuss, D. Hypovirulence: Mycoviruses at the fungal–plant interface. Nat Rev Microbiol 3, 632–642 (2005). https://doi.org/10.1038/nrmicro1206

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