Abstract
GTP-binding protein (G-protein) and regulator of G-protein signaling (RGS) mediated signal transduction are critical in the growth and virulence of the rice blast pathogen Magnaporthe oryzae. We have previously reported that there are eight RGS and RGS-like proteins named MoRgs1 to MoRgs8 playing distinct and shared regulatory functions in M. oryzae and that MoRgs1 has a more prominent role compared to others in the fungus. To further explore the unique regulatory mechanism of MoRgs1, we screened a M. oryzae cDNA library for genes encoding MoRgs1-interacting proteins and identified MoCkb2, one of the two regulatory subunits of the casein kinase (CK) 2 MoCk2. We found that MoCkb2 and the sole catalytic subunit MoCka1 are required for the phosphorylation of MoRgs1 at the plasma membrane (PM) and late endosome (LE). We further found that an endoplasmic reticulum (ER) membrane protein complex (EMC) subunit, MoEmc2, modulates the phosphorylation of MoRgs1 by MoCk2. Interestingly, this phosphorylation is also essential for the GTPase-activating protein (GAP) function of MoRgs1. The balance among MoRgs1, MoCk2, and MoEmc2 ensures normal operation of the G-protein MoMagA-cAMP signaling required for appressorium formation and pathogenicity of the fungus. This has been the first report that an EMC subunit is directly linked to G-protein signaling through modulation of an RGS-casein kinase interaction.
Highlights
Heterotrimeric G-protein signaling plays a fundamental role in regulating various cellular developmental processes in eukaryotic organisms
In the rice blast fungus M. oryzae, previous studies demonstrated that G-protein/cyclic adenosine monophosphate (cAMP) signaling are important for appressorium formation and pathogenicity
Phosphorylation of MoRgs1 by MoCk2 is modulated by MoEmc2 in cAMP signaling www.ec.js.edu.cn, grant recipient Z.Z).The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Summary
Heterotrimeric G-protein signaling plays a fundamental role in regulating various cellular developmental processes in eukaryotic organisms. In a conserved fashion, activated GPCRs induce conformational changes in the GDP-bound Gαβγ heterotrimer leading to the dissociation of GTPbound Gα from the Gβγ heterodimer [4]. GTP-bound Gα can convey signals to adenylyl cyclases (ACs) that modulate the levels of cyclic adenosine monophosphate (cAMP) and cAMP-dependent protein kinase A (PKA) pathways [5,6,7]. The regulator of G-protein signaling proteins (RGS) is known to serve as GTPase-activating proteins (GAP) for various Gα subunits of heterotrimeric G proteins [12,13,14]. Some RGS proteins contain additional domains such as the GoLoco motif that inhibits GDP dissociation [15]
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