Post mortem function of AtMC9 in xylem vessel elements

Authors

  • Benjamin Bollhöner,

    1. Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, Umeå, Sweden
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  • Bo Zhang,

    1. Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, Umeå, Sweden
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  • Simon Stael,

    1. Department of Plant Systems Biology, VIB, Gent, Belgium
    2. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
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  • Nicolas Denancé,

    1. UPS, UMR 5546, Laboratoire de Recherche en Sciences Végétales, Université de Toulouse, Castanet-Tolosan, France
    2. Centre National de la Recherche Scientifique, CNRS, UMR 5546, Laboratoire de Recherche en Sciences Végétales, Castanet-Tolosan, France
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  • Kirk Overmyer,

    1. Plant Biology, Department of Biosciences, University of Helsinki, Helsinki, Finland
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  • Deborah Goffner,

    1. UPS, UMR 5546, Laboratoire de Recherche en Sciences Végétales, Université de Toulouse, Castanet-Tolosan, France
    2. Centre National de la Recherche Scientifique, CNRS, UMR 5546, Laboratoire de Recherche en Sciences Végétales, Castanet-Tolosan, France
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  • Frank Van Breusegem,

    1. Department of Plant Systems Biology, VIB, Gent, Belgium
    2. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
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  • Hannele Tuominen

    Corresponding author
    1. Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, Umeå, Sweden
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Summary

  • Cell death of xylem elements is manifested by rupture of the tonoplast and subsequent autolysis of the cellular contents. Metacaspases have been implicated in various forms of plant cell death but regulation and execution of xylem cell death by metacaspases remains unknown.
  • Analysis of the type II metacaspase gene family in Arabidopsis thaliana supported the function of METACASPASE 9 (AtMC9) in xylem cell death. Progression of xylem cell death was analysed in protoxylem vessel elements of 3-d-old atmc9 mutant roots using reporter gene analysis and electron microscopy.
  • Protoxylem cell death was normally initiated in atmc9 mutant lines, but detailed electron microscopic analyses revealed a role for AtMC9 in clearance of the cell contents post mortem, that is after tonoplast rupture. Subcellular localization of fluorescent AtMC9 reporter fusions supported a post mortem role for AtMC9. Further, probe-based activity profiling suggested a function of AtMC9 on activities of papain-like cysteine proteases.
  • Our data demonstrate that the function of AtMC9 in xylem cell death is to degrade vessel cell contents after vacuolar rupture. We further provide evidence on a proteolytic cascade in post mortem autolysis of xylem vessel elements and suggest that AtMC9 is part of this cascade.

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