Biological control of chestnut blight caused by the filamentous ascomy
cete Cryphonectria parasitica can be achieved with a virus that infect
s this fungus, This hypovirus causes a perturbation pf fungal developm
ent that results in low virulence (hypovirulence), poor asexual sporul
ation, and female infertility without affecting fungal growth in cultu
re, At the molecular level, the virus is known to affect the transcrip
tion of a number of fungal genes, Two of these genes, Vir1 and Vir2, p
roduce abundant transcripts in noninfected strains of the fungus, but
the transcripts are not detectable in virus-infected strains, We repor
t here that these two genes encode the pheromone precursors of the Mat
-2 mating type of the fungus; consequently, these genes have been rena
med Mf2/1 and Mf2/2, To determine if the virus affects the mating syst
ems 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 repr
essed in virus-infected strains, The suppression of transcription of t
he pheromone precursor genes of this fungus could be the cause of the
mating defect of infected strains of the fungus, Although published re
ports suggest that a G alpha(i) subunit may be involved in this regula
tion, our results do not support this hypothesis, The prepropheromone
encoded by Mf1/1 is structurally similar to that of the prepro-p-facto
r of Schizosaccharomyces pombe, This is the first description of the c
omplete set of pheromone precursor genes encoded by a filamentous asco
mycete.