Signaling via the G protein α subunit FGA2 is necessary for pathogenesis inFusarium oxysporum

Cloning and disruption of fga1, the gene encoding the G protein α subunit FGA1 in phytopathogenic fungus Fusarium oxysporum, has been reported previously, and the fga1 disruptants showed altered colony morphology, increased heat resistance, reduced conidiation and pathogenicity. To further evaluate the role of G protein signaling in this fungus, cloning of fga2, which encodes the second Gα protein FGA2, was performed by PCR methods. The deduced primary structure of FGA2 (355 amino acid residues) showed high identity with other Gα proteins, which belong to class III of fungal Gα proteins. Disruption of fga2 led to higher heat resistance, similar to the fga1 disruptants, but pathogenicity was completely lost, unlike the fga1 disruptants. Alteration of colony morphology and conidiation, which was observed in the fga1 disruptants, was not observed in the fga2 disruptants. The fga1/fga2 double disruptants showed phenotypic alterations similar to the fga1 or fga2 single disruptants, but increase of heat resistance was much more pronounced than in each single disruptant.