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The growth of multicellular organisms relies on a precisely timed and coordinated cell division process from the onset of development. The MAPK cascade, composed of ANP-MKK6-MPK4 governs plant growth and development by regulating cytokinesis, the final step of cell division. Despite various efforts over the last decade, elucidating the detailed molecular mechanism by which MPK4 regulates plant cytokinesis has been challenging, mainly due to the severe growth defects of conventional mpk4 genetic mutants. Here, we applied a combinatorial genetics approach that integrates chemical genetics and forward genetic screening to identify novel downstream components of the MPK4 pathway in the regulation of cytokinesis, using Arabidopsis as a model system. During the suppressor screening of EMS-mutagenized chemical-inducible mpk4 mutants (impk4), we
isolated 39 suppressor mutants that reverted the root growth of impk4 to various extents. Strikingly, most of the identified causal SNVs include genes encoding components of the APC complex and nearby proteins, indicating that MPK4 regulates APC complex activity for the successful completion of cytokinesis. Our results emphasize the previously unrecognized link between MPK4 and CCS52B, which is one of the Cdh1-type coactivators of the Arabidopsis APC complex. Results from genetic, biochemical, cellular, and molecular investigation into the MPK4-CCS52B-cytokinesis pathway suggest that MPK4 plays a role in the timely control of cytokinesis through negative regulation of APCCCS52B complex.
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