Cochliobolus heterostrophus G-protein alpha and beta subunit double mutant reveals shared and distinct roles in development and virulence

Heterotrimeric G proteins transduce extracellular signals to control development in eukaryotes, including filamentous fungi. Targeted disruption of their α- and β-subunit genes has shown that fungal G proteins play essential roles in sexual and asexual sporulation, hyphal growth pattern and virulence. The G-protein β-subunit gene CGB1 of Cochliobolus heterostrophus, the agent of Southern leaf blight, is essential for virulence and sporulation, while one of the α-subunit genes, CGA1, has roles in several developmental pathways. We constructed a strain with insertions/deletions at both CGA1 and CGB1. The double mutant, like the single mutants, was deficient in mating and appressorium formation and its hyphae followed a straight path rather than the typical meandering growth pattern on a hard surface. The two genes shared a combined role in determining pigmentation, surface hydrophobicity, and resistance to different stresses. However, in contrast to the single mutants, the double mutants developed white-gray to completely white colonies that are hydrophilic and form wet, autolytic-appearing patches. These phenotypes resemble some of those conferred by mutations in the MAPK gene CHK1, suggesting crosstalk between MAPK and G-protein pathways. Loss of signal-transduction functions, while reducing virulence, increases resistance to some stresses. A model is proposed for the interactions between the signaling pathways.

► We constructed Cochliobolus heterostrophus mutants deficient in G-protein α- and β-subunits. ► These mutants share some of the single mutants' development and virulence phenotypes. ► New relationships were found between the two genes in a few synthetic phenotypes. ► These phenotypes resemble some of those conferred by mutations in the MAPK gene CHK1. ► Evidence suggests crosstalk between MAPK and G-protein pathways.