AUTHOR=Tong Youmin , Wu Hao , Liu Zhenbang , Wang Zhangxun , Huang Bo 

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

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.01251

DOI=10.3389/fmicb.2020.01251

ISSN=1664-302X

ABSTRACT=<p>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<sub>i</sub>, in conidiation, stress resistance, and virulence in <italic>Metarhizium robertsii</italic>. MrGPA1 was localized in the mitochondria. <italic>MrGpa1</italic> deletion resulted in a significant reduction (47%) in the conidiation capacity, and reduced expression of several key conidiation-related genes, including <italic>fluG</italic>, <italic>flbD</italic>, <italic>brlA</italic>, <italic>wetA</italic>, <italic>phiA</italic>, and <italic>stuA</italic>. Further, <italic>MrGpa1</italic> disruption resulted in decreased fungal sensitivity to UV irradiation and thermal stress, as determined based on conidial germination of Δ<italic>MrGpa1</italic> and wild-type (WT) strains. Chemical stress analysis indicated that <italic>MrGpa1</italic> 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 <italic>Galleria mellonella</italic> larvae revealed decreased virulence of Δ<italic>MrGpa1</italic> 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 <italic>MrGpa1</italic> regulated intracellular cyclic AMP (cAMP) levels, but feeding with cAMP could not recover the appressorium formation rate of Δ<italic>MrGpa1.</italic> These observations suggest that <italic>MrGpa1</italic> contributes to the regulation of conidiation, UV irradiation, thermal stress response, antioxidant capacity, and cell wall integrity in <italic>M. robertsii</italic>. This gene is also involved in insect cuticle penetration during infection. These findings raise the possibility of designing powerful strategies for genetic improvement of <italic>M. robertsii</italic> conidiation capacity and virulence for killing pests.</p>