The appressorium of the rice blast fungus Magnaporthe oryzae remains mitotically active during post-penetration hyphal growth.
Saturday, 2016/12/03 | 06:26:36
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Jenkinson CB1, Jones K1, Zhu J1, Dorhmi S1, Hyun Khang C2. Fungal Genet Biol. 2016 Nov 23. pii: S1087-1845(16)30142-6. doi: 10.1016/j.fgb.2016.11.006. [Epub ahead of print] AbstractTo 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.
See: https://www.ncbi.nlm.nih.gov/pubmed/27890626
Fig. 1. Appressorial mitotic dynamics of M. oryzae during invasion of rice cells. (A) Confocal images showing two focal planes of the same M. oryzae strain CKF110 infection at 36 hours post inoculation (hpi). This M. oryzae strain expresses histone H1-mRFP (red) and cytoplasmic EYFP (green). The IH focal plane (bottom) is 7 μm below the appressorial focal plane (top). A single nucleus in the appressorium (white arrowhead) is clearly visible in the appressorial focal plane. The IH focal plane shows highly branched IH that have spread into adjoining host rice cells. Bar = 10 μm. (B) Another infection at the same growth stage as (A). The IH focal plane (bottom) is 8 μm below the appressorial focal plane (top). Note that there are two nuclei in the appressorium (white arrowhead). Bar = 10 μm. (C) Time-lapse confocal images selected from Video 1, showing three rounds of mitosis during initial host colonization by M. oryzae CKF1962, starting at 25 hpi. This strain expresses histone H1-tdTomato (red; nuclear localization throughout the cell cycle) and GFP-NLS (green; nuclear localization during interphase but cytoplasmic localization during mitosis). The first mitosis is appressorial (left column), followed by mitosis in IH (middle column), and finally another appressorial mitosis (right column). Nuclei entering mitosis are denoted with white arrows. The conidium (white asterisk) is undergoing autophagic cell death. Times are shown in hours:minutes:seconds. Bar = 5 μm. (D) Schematic representations of the observed sequences of the first three rounds of mitosis after host penetration. Red circles indicate nuclei. Numbers associated with arrows indicate the order of nuclear divisions. Arrows indicate the direction of nuclear migration. The diagram on the left represents the mitotic sequence of the infection site in Fig. 1C and Video 1. The other sequences (middle and right) are of independently observed infection sites. n = number of observed infection sites. (E) Schematic diagram illustrating the question of how an appressorial nucleus (∼2 μm in diameter) can migrate through the narrow penetration peg (∼0.7 μm in diameter) to enter the filamentous IH. (F) Time-lapse single plane confocal images of M. oryzae CKF1962 invading a rice cell. Left: merged tdTomato and bright-field; right: tdTomato alone (shown in white). Sequence shows the first appressorial nuclear division and migration supplying a nucleus to the filamentous IH. The middle panel shows an extreme elongation and constriction of a mitotic nucleus as it migrates through the penetration pore. Times are shown in minutes:seconds. Bar = 5 μm. |
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