Abstract
Arginine is a semi-essential amino acid that affects physiological and biochemical functions. The CPA2 gene in yeast encodes a large subunit of arginine-specific carbamoyl phosphate synthetase (CPS) and is involved in arginine biosynthesis. Here, an ortholog of yeast CPA2 was identified in the rice blast fungus Magnaporthe oryzae, and was named MoCPA2. MoCpa2 is an 1180-amino acid protein which contains an ATP grasp domain and two CPSase domains. Targeted deletion of MoCPA2 supported its role in de novo arginine biosynthesis in M. oryzae as mutant phenotypes were complemented by arginine but not ornithine. The ΔMocpa2 mutant exhibited defects in asexual development and pathogenicity but not appressorium formation. Further examination revealed that the invasive hyphae of the ΔMocpa2 mutant were restricted mainly to the primary infected cells. In addition, the ΔMocpa2 mutant was unable to induce a plant defense response and had the ability to scavenge ROS during pathogen-plant interactions. Structure analysis revealed that the ATP grasp domain and each CPS domain were indispensable for the proper localization and full function of MoCpa2. In summary, our results indicate that MoCpa2 plays an important role in arginine biosynthesis, and affects growth, conidiogenesis, and pathogenicity. These results suggest that research into metabolism and processes that mediate amino acid synthesis are valuable for understanding M. oryzae pathogenesis.
Highlights
Phytopathogenic fungi cause diseases in humans, animals, and plants, and their ability to access the rich nutrient supply offered by living plants is one of the most obvious properties that distinguish pathogens from saprophytes (Divon and Fluhr, 2007)
There were no expression differences in late infectious stages (72 hpi; Figure 1). These results suggested that MoCPA2 likely plays an important role in asexual development and early infection in the rice blast fungus
To further examine the biological function of MoCPA2, the MoCPA2 coding region was replaced with the hygromycin resistance cassette (HPH) via homologous recombination, and the successful gene deletion mutant was confirmed by Southern blot analysis (Figure S1)
Summary
Phytopathogenic fungi cause diseases in humans, animals, and plants, and their ability to access the rich nutrient supply offered by living plants is one of the most obvious properties that distinguish pathogens from saprophytes (Divon and Fluhr, 2007). The regulatory systems include nitrogen metabolite repression (NMR) and carbon catabolite repression (CCR) to ensure the use of preferred sources of nitrogen (ammonium and L-glutamine) and carbon (glucose), respectively (Wilson et al, 2007, 2012; Wilson and Talbot, 2009; Fernandez et al, 2012). Both NMR and CCR are controlled by a Tor signaling pathway that regulates growth in response to nutrient availability (Franceschetti et al, 2011). All three of these enzymes control the growth, asexual development, and pathogenicity of the rice blast fungus (Du et al, 2013, 2014)
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