MoCpa1-mediated arginine biosynthesis is crucial for fungal growth, conidiation, and plant infection of Magnaporthe oryzae.

Arginine is an important amino acid involved in processes such as cell signal transduction, protein synthesis, and sexual reproduction. To understand the biological roles of arginine biosynthesis in pathogenic fungi, we used Cpa1, the carbamoyl phosphate synthase arginine-specific small chain subunit in Saccharomyces cerevisiae as a query to identify its ortholog in the Magnaporthe oryzae genome and named it MoCpa1. MoCpa1 is a 471-amino acid protein containing a CPSase_sm_chain domain and a GATase domain. MoCpa1 transcripts were highly expressed at the conidiation, early-infection, and late-infection stages of the fungus. Targeted deletion of the MoCPA1 gene resulted in a ΔMocpa1 mutant exhibiting arginine auxotrophy on minimum culture medium (MM), confirming its role in de novo arginine biosynthesis. The ΔMocpa1 mutant presented significantly decreased sporulation with some of its conidia being defective in morphology. Furthermore, the ΔMocpa1 mutant was nonpathogenic on rice and barley leaves, which was a result of defects in appressorium-mediated penetration and restricted invasive hyphal growth within host cells. Addition of exogenous arginine partially rescued conidiation and pathogenicity defects on the barley and rice leaves, while introduction of the MoCPA1 gene into the ΔMocpa1 mutant fully complemented the lost phenotype. Further confocal microscopy examination revealed that MoCpa1 is localized in the mitochondria. In summary, our results demonstrate that MoCpa1-mediated arginine biosynthesis is crucial for fungal development, conidiation, appressorium formation, and infection-related morphogenesis in M. oryzae, thus serving as an attractive target for mitigating obstinate fungal plant pathogens. KEY POINTS: • MoCpa1 is important for aerial hyphal growth and arginine biosynthesis. • MoCpa1 is pivotal for conidial morphogenesis and appressorium formation. • MoCpa1 is crucial for full virulence in M. oryzae.