Eight RGS and RGS-like proteins orchestrate growth, differentiation, and pathogenicity of Magnaporthe oryzae.

Haifeng Zhang,Kaiyue Liu,Jiansheng Wang,Xia Yan,Wei Tang,Qian Huang,Zhengyi Wang,Xiaobo Zheng,Zhengguang Zhang,Yue Chen,Xin Zhang,Zhongqiang Qi,Ping Wang,Barbara Jane Howlett

doi:10.1371/journal.ppat.1002450

Abstract

A previous study identified MoRgs1 as an RGS protein that negative regulates G-protein signaling to control developmental processes such as conidiation and appressorium formation in Magnaporthe oryzae. Here, we characterized additional seven RGS and RGS-like proteins (MoRgs2 through MoRgs8). We found that MoRgs1 and MoRgs4 positively regulate surface hydrophobicity, conidiation, and mating. Indifference to MoRgs1, MoRgs4 has a role in regulating laccase and peroxidase activities. MoRgs1, MoRgs2, MoRgs3, MoRgs4, MoRgs6, and MoRgs7 are important for germ tube growth and appressorium formation. Interestingly, MoRgs7 and MoRgs8 exhibit a unique domain structure in which the RGS domain is linked to a seven-transmembrane motif, a hallmark of G-protein coupled receptors (GPCRs). We have also shown that MoRgs1 regulates mating through negative regulation of Gα MoMagB and is involved in the maintenance of cell wall integrity. While all proteins appear to be involved in the control of intracellular cAMP levels, only MoRgs1, MoRgs3, MoRgs4, and MoRgs7 are required for full virulence. Taking together, in addition to MoRgs1 functions as a prominent RGS protein in M. oryzae, MoRgs4 and other RGS and RGS-like proteins are also involved in a complex process governing asexual/sexual development, appressorium formation, and pathogenicity.

Highlights

Signal transduction cascades are the primary means by which external cues are communicated to the nuclei of eukaryotic organisms including fungi
We provided evidence to demonstrate that, in addition to MoRgs1 functioning as a prominent Regulators of G-protein signaling (RGS) protein, other RGS and RGS-like proteins are involved in a complex process to control asexual/sexual development, appressorium differentiation and penetration, and pathogenicity of M. oryzae
Mutants blocked at appressorium formation or appressorial turgor generation fail to infect healthy rice plants [18]

Summary

Introduction

Signal transduction cascades are the primary means by which external cues are communicated to the nuclei of eukaryotic organisms including fungi. Heterotrimeric guanine-nucleotide binding protein (G-protein) signaling is one of the most important mechanisms by which eukaryotic cells sense extracellular signals and integrate them into intrinsic signal transduction pathways, such as the cyclic AMP (cAMP)-dependent signaling pathway. Heterotrimeric G-proteins are activated by the seven-transmembrane-spanning family of receptors [1]. Binding of signal ligands to such receptors promotes an exchange of GDP to GTP on the Ga subunit, which triggers a reciprocal conformational change and dissociation from the Gbc heterodimer [2]. The activated G-proteins are later desensitized by the intrinsic GTPase activity of the Ga subunit, followed by re-association with the Gbc complex. The guanine nucleotide state of the Ga subunit plays a critical role in controlling G-protein signaling [2]. G-proteins are involved in the regulation of a variety of cellular functions in vegetative growth and/or pathogenic development, such as conidiation, infection structure differentiation, and pathogenicity [7,8,9]

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