Characteristics of a Regulator of G-Protein Signaling (RGS) rgsC in Aspergillus fumigatus.

Young Kim,Kwang-Soo Shin,In-Beom Heo,Jae-Hyuk Yu

doi:10.3389/fmicb.2017.02058

Abstract

The regulator of G-protein signaling (RGS) proteins have a conserved RGS domain that facilitates the intrinsic GTPase activity of an activated Gα subunit of heterotrimeric G protein, thereby attenuating signal transduction. Among six predicted RGS proteins in the opportunistic human pathogenic fungus Aspergillus fumigatus, only three (FlbA, GprK, and Rax1) have been studied. The unexplored RgsC composed of the Phox-associated (PXA), RGS, Phox homology (PX), and Nexin_C superfamily domains is highly conserved in many ascomycete fungi, suggesting a crucial role of RgsC in fungal biology. To address this, we have investigated functions of the rgsC gene. The deletion (Δ) of rgsC causes impaired vegetative growth and asexual development coupled with reduced expression of key developmental regulators. Moreover, ΔrgsC results in accelerated and elevated conidial germination regardless of the presence or absence of an external carbon source. Furthermore, ΔrgsC causes reduced conidial tolerance to oxidative stress. In addition, activities and expression of catalases and superoxide dismutases (SODs) are severely decreased in the ΔrgsC mutant. The deletion of rgsC results in a slight reduction in conidial tolerance to cell wall damaging agents, yet significantly lowered mRNA levels of cell wall integrity/biogenesis transcription factors, indicating that RgsC may function in proper activation of cell wall stress response. The ΔrgsC mutant exhibits defective gliotoxin (GT) production and decreased virulence in the wax moth larvae, Galleria mellonella. Transcriptomic studies reveal that a majority of transporters is down-regulated by ΔrgsC and growth of the ΔrgsC mutant is reduced on inorganic and simple nitrogen medium, suggesting that RgsC may function in external nitrogen source sensing and/or transport. In summary, RgsC is necessary for proper growth, development, stress response, GT production, and external nutrients sensing.

Highlights

Heterotrimeric G-protein (G-protein) signaling plays pivotal roles in sensing and responding to internal/external signals and various stresses
Basic units of the G-protein signaling system typically include a G protein-coupled receptor (GPCR), regulators of G protein signaling (RGS), a heterotrimeric G protein composed of α, β, and γ subunits, and a variety of effectors (Li et al, 2007)
regulators of G-protein signaling (RGS) proteins are a family of multifunctional signaling regulators having the capacity to bind to activated Gα subunits

Summary

Introduction

Heterotrimeric G-protein (G-protein) signaling plays pivotal roles in sensing and responding to internal/external signals and various stresses. A canonical G-protein signaling pathway is typically controlled by three components; G-protein coupled receptors (GPCRs), regulators of G-protein signaling (RGS), and heterotrimeric G proteins composed of α, β, and γ subunits (Lafon et al, 2005; Yu, 2006). In the human pathogenic fungus Aspergillus fumigatus, six genes predicted to encode RGS domain proteins have been identified (flbA, gprK, rgsA, rax, rgsC, and rgsD). It has been reported that the putative hybrid GPCR-RGS protein GprK plays an important role in upstream regulation of G-protein signaling and contributes to proper asexual sporulation, gliotoxin (GT) production, and oxidative stress responses (Jung et al, 2016). Rax was shown to positively control vegetative growth and asexual development, and modulate trehalose amount and cell wall melanin levels in conidia, and conidia resistance against hydrogen peroxide (Igbalajobi et al, 2017)

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Conclusion