EXTENSIVE ALTERATION OF FUNGAL GENE TRANSCRIPT ACCUMULATION AND ELEVATION OF G-PROTEIN-REGULATED CAMP LEVELS BY A VIRULENCE-ATTENUATING HYPOVIRUS

Persistent infection of the chestnut blight fungus Cryphonectria paras itica with the prototypic hypovirus CHV1-713 results in attenuation of fungal virulence (hypovirulence) and reduced accumulation of the GTP- binding (G) protein alpha subunit CPG-1. Transgenic cosuppression of C PG-1 accumulation in the absence of virus infection also confers hypov irulence. We now report the use of mRNA differential display to examin e the extent to which virus infection alters fungal gene transcript ac cumulation and to assess the degree to which modification of CPG-1 sig nal transduction contributes to this alteration. More than 400 PCR pro ducts were identified that either increased (296 products) or decrease d (127 products) in abundance as a result of virus infection. Signific antly, 65% of these products exhibited similar changes as a result of CPG-1 cosuppression in the absence of virus infection. We also report that both virus infection and CPG-1 cosuppression elevate cAMP levels 3- to 5-fold. Additionally, it was possible to mimic the effect of vir us infection and CPG-1 cosuppression on transcript accumulation for re presentative fungal genes by drug-induced elevation of cAMP levels. Th ese results strengthen and extend previous indications that hypovirus infection causes a significant and persistent alteration of fungal gen e expression/transcript accumulation. They further show that this alte ration is primarily mediated through modification of the CPG-1 signali ng pathway and suggest that, similar to mammalian G(i) alpha subunits, CPG-1 functions as a negative modulator of adenylyl cyclase. Finally, these results suggest a role for G-protein-regulated cAMP accumulatio n in hypovirus-mediated alteration of fungal gene expression.