The appressorium of the rice blast fungus Magnaporthe oryzae remains mitotically active during post-penetration hyphal growth

•M. oryzae appressoria remain mitotically active during IH proliferation.•Sister chromatids separate within the appressorium.•A mitotic nucleus undergoes extreme constriction and elongation through the penetration peg.

To investigate the mitotic dynamics of an appressorium, we used live-cell confocal imaging of a fluorescence-based mitotic reporter strain of Magnaporthe oryzae. We present evidence that the M. oryzae appressorium remains viable and mitotically active well after host penetration. These results suggest the potential roles of the appressorium during post-penetration proliferation of invasive hyphae. Our studies also revealed that a mitotic appressorial nucleus undergoes extreme constriction and elongation as it migrates through the penetration peg in a manner analogous to mitosis during cell-to-cell movement of invasive hyphae. Understanding the mechanisms underlying these pathogen-specific nuclear dynamics may provide new targets for disease control.