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

Abstract

Regulators of G protein signaling (RGSs) are proteins that negatively regulate G protein signal transduction. In this study, seven putative RGSs were characterized in the nematode-trapping (NT) fungus, Arthrobotrys oligospora. Deleting Rgs genes significantly increased intracellular cAMP levels, and caused defects in mycelia growth, stress resistance, conidiation, trap formation, and nematocidal activity. In particular, the ΔAoFlbA mutant was unable to produce conidia and traps. Transcriptomic analysis showed that amino acid metabolic and biosynthetic processes were significantly enriched in the ΔAoFlbA mutant compared to WT. Interestingly, Gas1 family genes are significantly expanded in A. oligospora and other NT fungi that produce adhesive traps, and are differentially expressed during trap formation in A. oligospora. Disruption of two Gas1 genes resulted in defective conidiation, trap formation, and pathogenicity. Our results indicate that RGSs play pleiotropic roles in regulating A. oligospora mycelial growth, development, and pathogenicity. Further, AoFlbA is a prominent member and required for conidiation and trap formation, possibly by regulating amino acid metabolism and biosynthesis. Our results provide a basis for elucidating the signaling mechanism of vegetative growth, lifestyle transition, and pathogenicity in NT fungi.

AoPEX1 and AoPEX6 Are Required for Mycelial Growth, Conidiation, Stress Response, Fatty Acid Utilization, and Trap Formation in Arthrobotrys oligospora

“…In addition, many downregulated genes were enriched in MAPK signaling, which is in line with previous reports ( 40 ). For example, deletion of G-protein signaling regulators caused a considerable reduction in conidiation and trap formation ( 41 , 42 ), and disruption of MAPK signaling components, such as Slt2 and Fus3, resulted in trap formation defects in A. oligospora ( 40 , 43 , 44 ). A previous study hypothesized that the remains of organisms that died during mass extinctions are rich in carbon but poor in nitrogen, such that directly capturing nitrogen-rich living organisms would confer predatory fungi a competitive advantage over strictly saprophytic fungi ( 45 ).…”

Aolatg1 and Aolatg13 Regulate Autophagy and Play Different Roles in Conidiation, Trap Formation, and Pathogenicity in the Nematode-Trapping Fungus Arthrobotrys oligospora

“…G-protein signaling plays an indispensable role in trap formation of A. oligospora . There are several evidences corroborating this hypothesis, such as deletion of flbA , which encodes a regulator of G-protein signaling, abrogates trap formation in A. oligospora ( Ma et al., 2021 ). Moreover, hog1 deletion caused a reduction in trap formation and predation efficiency in A. oligospora ( Kuo et al., 2020 ).…”

“…When stimulated by nematodes or other inducing factors, A. oligospora produces adhesive networks, indicating a switch from the saprophytic lifestyle to the predacious stage ( Nordbring-Hertz, 2004 ; Yang et al., 2011 ). Since the sequencing of A. oligospora genome, an increasing number of studies has focused on the mechanism underlying trap formation, and several signaling proteins, such as regulators of G-protein, G-protein subunits and small GTPases, have been shown to regulate trap morphogenesis and lifestyle switch ( Yang et al., 2018 ; Yang et al., 2020 ; Bai et al., 2021 ; Ma et al., 2021 ; Yang et al., 2021 ). Moreover, three orthologous Atg proteins have been identified in A. oligospora : deletion of Aolatg8 blocked autophagy and abolished conidiation and trap formation ( Chen et al., 2013 ), whereas deletion of Aolatg4 and Aolatg5 impaired autophagy and resulted in a reduction in conidia yields, cell nucleus number, and trap production ( Zhou et al., 2020 ; Zhou et al., 2021 ).…”

Transcriptomic Analysis Reveals That Rho GTPases Regulate Trap Development and Lifestyle Transition of the Nematode-Trapping Fungus Arthrobotrys oligospora

“… Arthrobotrys oligospora is a typical NT fungus that forms adhesive networks to capture nematodes and has been widely studied to understand the mechanisms of trap formation ( 9 ). Since the genome of A. oligospora was sequenced ( 4 ), several signaling proteins involved in the regulation of trap formation and pathogenicity, such as mitogen-activated protein kinase (MAPK) ( 10 ), G protein β subunit ( 11 ), regulators of G protein signaling ( 12 ), and small GTPases Rab-7A ( 13 ) and Ras family ( 14 ), have been identified. These studies demonstrate the complexity of the cellular processes involved in trap formation and lifestyle transition, regulated by various signaling proteins and pathways in NT fungi.…”