The DNA damage signal transducer ortholog <Emphasis Type="Italic">Mop53BP1</Emphasis> is required for proper appressorium differentiation and pathogenicity in <Emphasis Type="Italic">Pyricularia oryzae</Emphasis>

Appressorium differentiation, one of the most important steps in pathogenesis by the rice blast fungus, Pyricularia oryzae, is strongly coordinated with the cell cycle. In this study, we identified an ortholog gene of 53BP1, which encodes a signal transducer protein that participates in G2-M cell cycle checkpoint in higher eukaryotes, in the genome of P. oryzae and characterized the phenotype of deletion and overexpression mutants. Deletion mutants showed no significant deficiency in vegetative growth compared to wild-type and complemented strains, even on the media containing DNA-damaging agents. However, these null mutants had abnormal appressoria and formed more appressoria per conidium than in the wild type and were unable to penetrate the epidermis of rice leaves. eGFP-fused Mop53BP1 and qRT-PCR analyses revealed that Mop53BP1 is expressed during the first hours of appressorium formation. In addition, in overexpression mutants, Mop53BP1 localized to nuclei during all stages of appressorium maturation and penetration, and the mutants were resistant to the microtubule inhibitor benomyl, suggesting that Mop53BP1 is nuclear protein and may have some role related to microtubules.