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Role of two metacaspases in development and pathogenicity of the Rice Blast fungus, Magnaporthe oryzae

By Jessie Fernandez, Victor Lopezz, Lisa Kinch, Mariel A. Pfeifer, HIllery A Gray, Nalleli Orth, Nick V. Grishin, Chang Hyun Khang, Kim Orth

Posted 11 Dec 2020
bioRxiv DOI: 10.1101/2020.12.10.420794

Rice blast disease caused by Magnaporthe oryzae is a devastating disease of cultivated rice worldwide. Infections by this fungus lead to a significant reduction in rice yields and threats to food security. To gain better insight into growth and cell death in M. oryzae during infection, we characterized two predicted M. oryzae metacaspase proteins, MoMca1 and MoMca2. These proteins appear to be functionally redundant and are able to complement the yeast Yca1 homologue. Biochemical analysis revealed that M. oryzae metacaspases exhibited Ca2+ dependent caspase activity in vitro. Deletion of both MoMca1 and MoMca2 in M. oryzae resulted in reduced sporulation, delay in conidial germination and attenuation of disease severity. In addition, the double {Delta}Momca1mca2 mutant strain showed increased radial growth in the presence of oxidative stress. Interestingly, the {Delta}Momca1mca2 strain showed an increase accumulation of insoluble aggregates compared to the wild-type strain during vegetative growth. Our findings suggest that MoMca1 and MoMca2 promote the clearance of insoluble aggregates in M. oryzae, demonstrating the important role these metacaspases have in fungal protein homeostasis. Furthermore, these metacaspase proteins may play additional roles, like in regulating stress responses, that would help maintain the fitness of fungal cells required for host infection.

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