G-Protein Subunit Gαi in Mitochondria, MrGPA1, Affects Conidiation, Stress Resistance, and Virulence of Entomopathogenic Fungus Metarhizium robertsii

Abstract

G proteins are critical modulators or transducers in various transmembrane signaling systems. They play key roles in numerous biological processes in fungi, including vegetative growth, development of infection-related structures, asexual conidiation, and virulence. However, functions of G proteins in entomopathogenic fungi remain unclear. Here, we characterized the roles of MrGPA1, a G-protein subunit Gα i , in conidiation, stress resistance, and virulence in Metarhizium robertsii. MrGPA1 was localized in the mitochondria. MrGpa1 deletion resulted in a significant reduction (47%) in the conidiation capacity, and reduced expression of several key conidiation-related genes, including fluG, flbD, brlA, wetA, phiA, and stuA. Further, MrGpa1 disruption resulted in decreased fungal sensitivity to UV irradiation and thermal stress, as determined based on conidial germination of MrGpa1 and wild-type (WT) strains. Chemical stress analysis indicated that MrGpa1 contributes to fungal antioxidant capacity and cell wall integrity, but is not involved in tolerance to antifungal drug and osmotic stress. Importantly, insect bioassays involving (topical inoculation and injection) of Galleria mellonella larvae revealed decreased virulence of MrGpa1 strain after cuticle infection. This was accompanied by decreased rates of appressorium formation and reduced expression of several cuticle penetration-related genes. Further assays showed that MrGpa1 regulated intracellular cyclic AMP (cAMP) levels, but feeding with cAMP could not recover the appressorium formation rate of MrGpa1. These observations suggest that MrGpa1 contributes to the regulation of conidiation, UV irradiation, thermal stress response, antioxidant capacity, and cell wall integrity in M. robertsii. This gene is also involved in insect cuticle penetration during infection. These findings raise the possibility of designing powerful strategies for genetic improvement of M. robertsii conidiation capacity and virulence for killing pests.

AaPKAc Regulates Differentiation of Infection Structures Induced by Physicochemical Signals From Pear Fruit Cuticular Wax, Secondary Metabolism, and Pathogenicity of Alternaria alternata

“…surface hydrophobin Mpg1 or a transmembrane protein Pth11 leads to a defect in contact-induced appressorium formation. The surface-induced appressorium defect in all two deletion mutants can be bypassed by the addition of cAMP (Liu and Dean, 1997). These results indirectly verified the role of the cAMP-PKA pathway on the infection structure formation in FIGURE 6 | Effect of AaPKAc on the pathogenicity of A. alternata.…”

Functional analysis of seven regulators of G protein signaling (RGSs) in the nematode-trapping fungus Arthrobotrys oligospora

“…Both the Gα-GTP and Gβγ heterocomplexes can transmit signals to downstream effectors, including cAMP-dependent protein kinase A (PKA), ion channels, and mitogen-activated protein kinases [ 1 , 3 ]. In fungi, G proteins are associated with numerous biological processes, including sexual and asexual reproduction, virulence, and response to external signal stimuli [ 1 , 4 , 5 ]. For example, GpaB (Gα) regulates growth and asexual development via the cAMP/PKA signal transduction pathway in Aspergillus fumigatus [ 6 ], whereas SfaD (Gβ) and GpgA (Gγ) regulate trehalose hydrolysis, conidial germination, hyphal growth, and gliotoxin biosynthesis [ 7 ].…”

Host-Induced Gene Silencing of a G Protein α Subunit Gene CsGpa1 Involved in Pathogen Appressoria Formation and Virulence Improves Tobacco Resistance to Ciboria shiraiana

“…Then, Gα and Gβγ activate downstream effectors, including adenylyl cyclases, mitogen-activated protein kinases (MAPK)s, ion channels, phosphodiesterases, and phospholipases [14][15][16][17]. Previous studies have shown that Gα subunits are involved in the regulation of various physiological processes of fungi [18][19][20]. In Metarhizium robertsii, MrGpa1 deletion caused reductions in the number of conidia formed, germination, stress sensitivity, and pathogenicity [18].…”

“…Previous studies have shown that Gα subunits are involved in the regulation of various physiological processes of fungi [18][19][20]. In Metarhizium robertsii, MrGpa1 deletion caused reductions in the number of conidia formed, germination, stress sensitivity, and pathogenicity [18]. In Aspergillus fumigatus, three Gα subunits were found and shown to participate in regulation of hyphae growth, asexual development, germination, oxidative stress tolerance, and gliotoxin production [19].…”

“…Hypertrophy sorosis scleroteniosis caused by C. shiraiana is the most destructive fungal disease in the mulberry fruit industry [34]. The G protein α subunits were shown to be involved in fungal development, appressorium formation, and pathogenicity [13,18,20]. However, the function of the G protein α subunit in C. shiraiana development and pathogenicity remains unclear.…”