Identification and functional characterization of a Phytophthora infestans G-protein γ subunit

Signal transduction pathways lie at the base of a wide variety of cellular processes. We focus on G- protein signalling in the oomycete Phythopthora infestans, a notorious pathogen that causes late blight in potato and tomato. Previous research based on silencing and overexpression of the Gα and Gβ subunit genes in P. infestans, showed that heterotrimeric G protein signalling plays a role in zoospore motility, sporangial development and virulence (Latijnhouwers and Govers 2003; Latijnhouwers et al. 2004). Initial Contrary to Gα and Gβ genome annotation failed to identify did not reveal a typical Gγ gene, in P. infestans but a but recently a metagenome study revealed a potential candidate indicated presence of a Gγ subunit in P. infestans (De Mendoza et al. 2014). To test the validity and elucidate its function the predicted P. infestans Gγ subunit gene (Pigpg1) was cloned and investigated inmore detail. It is a two exon gene encoding a protein of 71 amino acids, shorter than most previously reported Gγ subunits. Overall the similarity with non-oomycete Gγ subunits is low, with only the most conserved amino acids maintained. In contrast, the
similarity with its homologs in other oomycetes is high. Pigpg1 is expressed in all developmental stages and shows a similar expression profile as the Gβ gene Pigpb1. Downregulation of Pigpg1 in P. infestans was achieved by homology-dependent gene silencing. Current efforts focus at characterizing the Pigpg1- deficient mutants, assessing whether Pigpg1 is a functional Gγ subunit and elucidating its potential role in development and virulence.