title: NQK1/NtMEK1 is a MAPKK that acts in the NPK1 MAPKKK-mediated MAPK cascade and is required for plant cytokinesis.
abstract: The tobacco protein kinase NPK1 is a MAPKKK that regulates formation of the cell plate during cytokinesis. In the present study, we have identified tobacco NQK1/NtMEK1 and NRK1 as a MAPKK and a MAPK, respectively, downstream of NPK1. NQK1/NtMEK1 complements the mutation in the PBS2 MAPKK gene of yeast in a manner that depends on both NPK1 and its activator, NACK1, a kinesin-like protein. Active NPK1 and NQK1/NtMEK1 phosphorylate and activate NQK1/NtMEK1 and NRK1, respectively. Both NQK1/NtMEK1 and NRK1, as well as NPK1, are activated at the late M phase of the cell cycle in tobacco cells, and they are rapidly inactivated by depolymerization of phragmoplast microtubules. These results suggest the existence of a MAPK cascade that consists of NPK1, NQK1/NtMEK1, and NRK1 and functions in a process related to the architecture of phragmoplasts at the late M phase of the cell cycle. Overexpression of kinase-negative NQK1/NtMEK1 in tobacco cells generates multinucleate cells with incomplete cross-walls. Arabidopsis plants with a mutation in the ANQ1 gene, an ortholog of NQK1/NtMEK1, display a dwarf phenotype, with unusually large cells that contain multiple nuclei and cell-wall stubs in various organs. In addition, anq1 homozygotes set fewer flowers and produce large and malformed pollen grains with a tetrad structure. Thus, NQK1/NtMEK1 (ANQ1) MAPKK appears to be a positive regulator of plant cytokinesis during meiosis as well as mitosis.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Soyano
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Nishihama
authors.forename: Kayoko
authors.initials: K
authors.lastname: Morikiyo
authors.forename: Masaki
authors.initials: M
authors.lastname: Ishikawa
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Machida
mesh_terms: D000818:Animals; D017360:Arabidopsis; D002455:Cell Division / Q000502:physiology*; D004789:Enzyme Activation; D018506:Gene Expression Regulation, Plant; D066298:In Vitro Techniques; D048369:MAP Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008870:Microtubules / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008938:Mitosis / Q000502:physiology*; D010766:Phosphorylation; D010940:Plant Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D011817:Rabbits; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics*; D020798:Two-Hybrid System Techniques
chemical_list: D010940:Plant Proteins; D011994:Recombinant Proteins; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; C082276:NPK1 protein, Nicotiana tabacum; D048369:MAP Kinase Kinase 1; C429547:Mek1 protein, Nicotiana tabacum; D020929:Mitogen-Activated Protein Kinase Kinases