Differential expression of two hydrophobin genes (Pgh1 and Pgh2) from the biological control agent Phlebiopsis gigantea.

Phlebiopsis gigantea has been widely used as the biocontrol fungus against the root and butt rot disease of conifers caused by Heterobasidion annosum. We investigated the regulation of two hydrophobin genes (Pgh1 and Pgh2) in strong and weak antagonistic isolates of the biological control agent P. gigantea under diverse substrate conditions. Transcript abundance of Pgh1 was higher in single cultures of strong performing isolates than in the weak performing isolates at the early and late stages of the fungal growth (P =0.05). Higher fold transcript changes of Pgh1 and Pgh2 were observed in the strong performing isolates at the early stage of the antagonistic interaction on modified Norkrans sawdust agar medium compared to the weak performing isolates. Higher transcript abundance of the two genes was also observed during growth in submerged compared to surface agar cultures (P<0.003 and P=0.0001 for Pgh1 and Pgh2, respectively). No correlation between antagonistic ability and sequence characteristics of either gene was found but a significant correlation was found between some strong performing isolates and the expression of Pgh1. Regulatory patterns of both Pgh1 and Pgh2 suggest a role during early stages of interaction between the two fungi and their potential roles in the biological control process is discussed.