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Mol Cell Biol, February 1998, p. 953-959, Vol. 18, No. 2
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Viral Repression of Fungal Pheromone Precursor Gene Expression

Lei Zhang,dagger Rudeina A. Baasiri,Dagger and Neal K. Van Alfen*

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843-2132

Received 10 March 1997/Returned for modification 23 April 1997/Accepted 6 June 1997

Biological control of chestnut blight caused by the filamentous ascomycete Cryphonectria parasitica can be achieved with a virus that infects this fungus. This hypovirus causes a perturbation of fungal development that results in low virulence (hypovirulence), poor asexual sporulation, and female infertility without affecting fungal growth in culture. At the molecular level, the virus is known to affect the transcription of a number of fungal genes. Two of these genes, Vir1 and Vir2, produce abundant transcripts in noninfected strains of the fungus, but the transcripts are not detectable in virus-infected strains. We report here that these two genes encode the pheromone precursors of the Mat-2 mating type of the fungus; consequently, these genes have been renamed Mf2/1 and Mf2/2. To determine if the virus affects the mating systems of both mating types of this fungus, the pheromone precursor gene, Mf1/1, of a Mat-1 strain was cloned and likewise was found to be repressed in virus-infected strains. The suppression of transcription of the pheromone precursor genes of this fungus could be the cause of the mating defect of infected strains of the fungus. Although published reports suggest that a Galpha i subunit may be involved in this regulation, our results do not support this hypothesis. The prepropheromone encoded by Mf1/1 is structurally similar to that of the prepro-p-factor of Schizosaccharomyces pombe. This is the first description of the complete set of pheromone precursor genes encoded by a filamentous ascomycete.

* Corresponding author. Mailing address: Department of Plant Pathology and Microbiology, Texas A&M University, Room 120 L. F. Peterson Building, College Station, TX 77843-2132. Phone: (409) 845-8288. Fax: (409) 845-6483. E-mail: vanalfen{at}tamu.edu.

dagger Present address: Department of Internal Medicine and Biochemistry, Southwestern Medical School, Dallas, TX 75235-8573.

Dagger Present address: Department of Cell Biology, Baylor College of Medicine, Houston, TX 77030.




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