MoGLN2 Is Important for Vegetative Growth, Conidiogenesis, Maintenance of Cell Wall Integrity and Pathogenesis of Magnaporthe oryzae

Osakina Aron,Ammarah Shabbir,Min Wang,Birong Lin,Wajjiha Batool,Zonghua Wang,Lianyu Lin,Wei Tang

doi:10.3390/jof7060463

Abstract

Glutamine is a non-essential amino acid that acts as a principal source of nitrogen and nucleic acid biosynthesis in living organisms. In Saccharomyces cerevisiae, glutamine synthetase catalyzes the synthesis of glutamine. To determine the role of glutamine synthetase in the development and pathogenicity of plant fungal pathogens, we used S. cerevisiae Gln1 amino acid sequence to identify its orthologs in Magnaporthe oryzae and named them MoGln1, MoGln2, and MoGln3. Deletion of MoGLN1 and MoGLN3 showed that they are not involved in the development and pathogenesis of M. oryzae. Conversely, ΔMogln2 was reduced in vegetative growth, experienced attenuated growth on Minimal Medium (MM), and exhibited hyphal autolysis on oatmeal and straw decoction and corn media. Exogenous l-glutamine rescued the growth of ΔMogln2 on MM. The ΔMogln2 mutant failed to produce spores and was nonpathogenic on barley leaves, as it was unable to form an appressorium-like structure from its hyphal tips. Furthermore, deletion of MoGLN2 altered the fungal cell wall integrity, with the ΔMogln2 mutant being hypersensitive to H2O2. MoGln1, MoGln2, and MoGln3 are located in the cytoplasm. Taken together, our results shows that MoGLN2 is important for vegetative growth, conidiation, appressorium formation, maintenance of cell wall integrity, oxidative stress tolerance and pathogenesis of M. oryzae.

Highlights

Glutamine is a non-essential amino acid and is required in a vast number of metabolic pathways in living organisms
Three putative amino acid sequences that encode glutamine synthetase were identified and were named, based on a previous study, as MoGln1 (MGG_06888), MoGln2 (MGG_14279), and MoGln3 (MGG_02538) [57]
The three obtained MoGln amino acids were used for a blastP search to identify glutamine synthetase amino acid sequences in other fungi in the Fungi and Oomycetes genomics resources database and National Centre of Biotechnology Information

Summary

Introduction

Glutamine is a non-essential amino acid and is required in a vast number of metabolic pathways in living organisms. In humans glutamine is required in pathways such as nitrogen metabolism, ammonia detoxification, acid–base homeostasis, osmotic regulation, cell signaling, and proliferation [1,2]. It has been reported that glutamine acts as a precursor for neurotransmitters and a substrate for immune cells [3,4]. It has been shown that glutamine is used for the synthesis of biomolecules such as glucose, purines, pyrimidines, adenosine monophosphate, and nicotinamide adenine dinucleotide (NAD+) [5,6,7]. Since glutamine is a crucial metabolite in the metabolism of nitrogen, the intracellular glutamine levels are tightly regulated. Experimental data for various fungi have provided evidence that glutamine is a key effector of nitrogen catabolite repression (NCR), a regulatory cascade that is biased toward or prefers the utilization of reduced nitrogen sources such as ammonium and glutamine at the expense of more complex and energy-demanding ones, e.g., nitrate, purines, and proteins [8,9]

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