Phosphorylation of phosducin-like protein BDM-1 by protein kinase 2 (CK2) is required for virulence and G beta subunit stability in the fungal plant pathogen Cryphonectria parasitica.

Phosducin-like proteins are conserved regulatory components of G-protein signalling pathways, which mediate many physiological processes. Identified throughout eukaryotic genomes, they are thought to serve as regulators of G betagamma assembly. Cryphonectria parasitica, a plant pathogen and causative agent of chestnut blight, contains three G alpha, one G beta, one G gamma subunits and phosducin-like protein BDM-1 that have important roles in pigmentation, sporulation and virulence. Deletion of either G beta subunit or BDM-1 produces identical phenotypes. Additionally, we report that the G beta subunit is not detectable in absence of BDM-1. Given that the regulatory role of phosducin-like proteins may be influenced by protein kinase 2 (CK2), we confirmed that BDM-1 is a phosphoprotein that can be targeted by CK2 in vitro. Mutagenesis of the five putative CK2 sites revealed that native phosphorylation likely occurs at two locations. Strains bearing a single or double serine to alanine substitutions at those sites were significantly less virulent with only minor phenotypic changes from vegetative colonies. Therefore, CK2 activity appears to mediate key signals that are required for virulence, but not for vegetative growth. Expression of selected CK2 mutants resulted in reduced accumulation of the G beta subunit, suggesting that phosphorylation of BDM-1 influences G beta stability.