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The oomycete Phytophthora infestans is a notorious plant pathogen with potato and tomato as its primary hosts. Previous research showed that the heterotrimeric G-protein subunits Gα and Gβ have a role in zoospore motility and virulence, and sporangial development, respectively. Here, we present analyses of the gene encoding a Gγ subunit in P. infestans , Pigpg1 . The overall similarity of PiGPG1 with non-oomycete Gγ subunits is low, with only the most conserved amino acids maintained, but similarity with its homologs in other oomycetes is high. Pigpg1 is expressed in all life stages and shows a similar expression profile as the gene encoding the Gβ subunit, Pigpb1 . To elucidate its function, transformants were generated in which Pigpg1 is silenced or overexpressed and their phenotypes were analyzed. Pigpg1 -silenced lines produce less sporangia, which are malformed. Altogether, the results show that PiGPG1 is crucial for proper sporangia development and zoosporogenesis. PiGPG1 is a functional Gγ, and likely forms a dimer with PiGPB1 that mediates signaling. [ABSTRACT FROM AUTHOR]