Abstract
Heterotrimeric G-proteins are crucial for fungal growth and differentiation. The α subunits of heterotrimeric G-proteins play an essential role in controlling signal transduction. However, the function of G-protein α subunits in entomopathogenic fungi remains poorly understood. Two group II Gα subunits (MrGPA2 and MrGPA4) were characterized in the entomopathogenic fungus, Metarhizium robertsii. Bioinformatics analysis showed that the relationship between MrGPA2 and MrGPA4 was closer than that of other MrGPAs. Both green fluorescent protein (GFP)-tagged MrGPA2 and MrGPA4 were localized at the cytoplasm. Furthermore, ∆MrGpa2∆MrGpa4 double mutants showed remarkably reduced vegetative growth compared to the wild-type and single-mutant strains, which was accompanied by the downregulation of several growth-related genes, such as ssk2, pbs2, stuA, hog1, and ac. Only the ∆MrGpa2∆MrGpa4 double mutant was sensitive to Congo red stress. The insect bioassay demonstrated significantly attenuated virulence for the ∆MrGpa2∆MrGpa4 double mutant compared to the wild-type and single-mutant strains. Further analysis indicated that double deletion of MrGpa2 and MrGpa4 had no effect on appressorium formation but suppressed the expression levels of several virulence-related genes in the insect hemocoel. These findings demonstrate that MrGpa2 and MrGpa4 exhibit functional redundancy and contribute to the vegetative growth, stress tolerance, and pest control potential in M. robertsii.
Highlights
Insect-pathogenic fungi, as a biological control agent that can cause the death of many insects, represent an environmentally friendly alternative to existing insecticides [1]
We identified two N. crassa GNA-2 homologs, EFY98464.1 and EFZ00060.2, in M. robertsii, and named them MrGPA2 and MrGPA4, respectively
Conserved domain analysis revealed that MrGpa2 and MrGpa4 contained the guanine nucleotide-binding site of heterotrimeric G-protein (34-347-aa protein and 34-348-aa protein) (Figure 1A)
Summary
Insect-pathogenic fungi, as a biological control agent that can cause the death of many insects, represent an environmentally friendly alternative to existing insecticides [1]. Their use has been limited because of their slow killing speed, low sporulation rate, and sensitivity to high temperatures and UV stress. G-proteins are crucial for the regulation of cell function, division, and differentiation In filamentous fungi, they contribute to hyphal growth, conidiation, conidial germination, stress resistance, and virulence [6,7,8,9]. MrGPA2 and MrGPA4 of M. robertsii are orthologs of N. crassa GNA-2; there is no report on the function of MrGPA2 and MrGPA4 in entomopathogenic fungi
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