title: Phosphorylation of NtMAP65-1 by a MAP kinase down-regulates its activity of microtubule bundling and stimulates progression of cytokinesis of tobacco cells.
abstract: The tobacco mitogen-activated protein kinase (MAPK) cascade, which includes MAPK NRK1/NTF6, positively regulates expansion of the cytokinetic machinery known as the phragmoplast, which is followed by the synthesis of cell plates for completion of cell division. However, molecular events lying between the MAPK and phragmoplast expansion were not known. Here, we show that NRK1/NTF6 phosphorylates the threonine residue at position 579 in NtMAP65-1a, a microtubule-associated (MT-associated) protein. Levels of phosphorylated NtMAP65-1 increase during late M phase of the cell cycle, when NRK1/NTF6 is activated. Phosphorylated NtMAP65-1 is concentrated at the equator of phragmoplast, as is NRK1/NTF6. Overexpression of mutant forms of NtMAP65-1a that cannot be phosphorylated by NRK1 delays progression of the M phase and phragmoplast expansion, also rendering phragmoplast structures resistant to an MT-depolymerizing drug. Phosphorylation of NtMAP65-1 by NRK1/NTF6 down-regulates its MT-bundling activity in vitro. These results suggest that phosphorylation of NtMAP65-1 by NRK1/NTF6 also reduces its MT-bundling activity in vivo, which enhances destabilization and turnover of MTs at the phragmoplast equator, perhaps facilitating phragmoplast expansion.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Michiko
authors.initials: M
authors.lastname: Sasabe
authors.forename: Takashi
authors.initials: T
authors.lastname: Soyano
authors.forename: Yuji
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Seiji
authors.initials: S
authors.lastname: Sonobe
authors.forename: Hisako
authors.initials: H
authors.lastname: Igarashi
authors.forename: Tomohiko J
authors.initials: TJ
authors.lastname: Itoh
authors.forename: Mikiko
authors.initials: M
authors.lastname: Hidaka
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Machida
mesh_terms: D002453:Cell Cycle; D015536:Down-Regulation; D008856:Microscopy, Fluorescence; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D010957:Plasmids; D013912:Threonine / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology*
chemical_list: D008869:Microtubule-Associated Proteins; D013912:Threonine; D020928:Mitogen-Activated Protein Kinases