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Journal of Virology, January 2008, p. 740-754, Vol. 82, No. 2
0022-538X/08/$08.00+0     doi:10.1128/JVI.02015-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

A Host Factor Involved in Hypovirus Symptom Expression in the Chestnut Blight Fungus, Cryphonectria parasitica{triangledown} ,{dagger}

M. Iqbal Faruk, Ana Eusebio-Cope, and Nobuhiro Suzuki*

Agrivirology Laboratory, Research Institute for Bioresources, Okayama University, Kurashiki, Okayama 710-0046, Japan

Received 12 September 2007/ Accepted 22 October 2007

The prototype hypovirus CHV1-EP713 causes virulence attenuation and severe suppression of asexual sporulation and pigmentation in its host, the chestnut blight fungus, Cryphonectria parasitica. We identified a factor associated with symptom induction in C. parasitica using a transformation of C. parasitica strain EP155 with a full-length cDNA clone from a mild mutant virus strain, Cys(72). This was accomplished by using mutagenesis of the transformant fungal strain TCys(72)-1 by random integration of plasmid pHygR, conferring hygromycin resistance. The mutant, namA (after nami-gata, meaning wave shaped), showed an irregular fungal morphology with reduced conidiation and pigmentation while retaining similar levels of virulence and virus accumulation relative to TCys(72)-1- or Cys(72)-infected strain EP155. However, the colony morphology of virus-cured namA (VC-namA) was indistinguishable from those of EP155 and virus-cured TCys(72)-1 [VC-TCys(72)-1]. The phenotypic difference between VC-namA and VC-TCys(72)-1 was found only when these strains infected with the wild type or certain mutant CHV1-EP713 strains but not when infected with Mycoreovirus 1. Sequence analysis of inverse-PCR-amplified genomic DNA fragments and cDNA identified the insertion site of the mutagenic plasmid in exon 8 of the nam-1 gene. NAM-1, comprising 1,257 amino acids, shows sequence similarities to counterparts from other filamentous fungi and possesses the CorA domain that is conserved in a class of Mg2+ transporters from prokaryotes and eukaryotes. Complementation assays using the wild-type and mutant alleles and targeted disruption of nam-1 showed that nam-1 with an extension of the pHygR-derived sequence contributed to the altered phenotype in the namA mutant. The molecular mechanism underlying virus-specific fungal symptom modulation in VC-namA is discussed.

* Corresponding author. Mailing address: Agrivirology Laboratory, Research Institute for Bioresources, Okayama University, Kurashiki, Okayama 710-0046, Japan. Phone: 81(86) 434-1230. Fax: 81(86) 434-1232. E-mail: nsuzuki{at}rib.okayama-u.ac.jp

{triangledown} Published ahead of print on 31 October 2007.

{dagger} Supplemental material for this article may be found at http://jvi.asm.org/.

Journal of Virology, January 2008, p. 740-754, Vol. 82, No. 2
0022-538X/08/$08.00+0     doi:10.1128/JVI.02015-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Chiba, S., Salaipeth, L., Lin, Y.-H., Sasaki, A., Kanematsu, S., Suzuki, N. (2009). A Novel Bipartite Double-Stranded RNA Mycovirus from the White Root Rot Fungus Rosellinia necatrix: Molecular and Biological Characterization, Taxonomic Considerations, and Potential for Biological Control. J. Virol. 83: 12801-12812 [Abstract] [Full Text]  
  • Guo, L.-h., Sun, L., Chiba, S., Araki, H., Suzuki, N. (2009). Coupled termination/reinitiation for translation of the downstream open reading frame B of the prototypic hypovirus CHV1-EP713. Nucleic Acids Res 37: 3645-3659 [Abstract] [Full Text]  


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