title: Cell cycle function of a rice B2-type cyclin interacting with a B-type cyclin-dependent kinase.
abstract: Cyclin-dependent kinases (CDKs) are involved in the control of cell cycle progression. Plant A-type CDKs are functional homologs of yeast Cdc2/Cdc28 and are expressed throughout the cell cycle. In contrast, B-type CDK (CDKB) is a family of mitotic CDKs expressed during the S/M phase, and its precise function remains unknown. Here, we identified two B2-type cyclins, CycB2;1 and CycB2;2, as a specific partner of rice CDKB2;1. The CDKB2;1-CycB2 complexes produced in insect cells showed a significant level of kinase activity in vitro, suggesting that CycB2 binds to and activates CDKB2. We then expressed green fluorescent protein (GFP)-fused CDKB2;1 and CycB2;2 in tobacco BY2 cells to investigate their subcellular localization during mitosis. Surprisingly, the fluorescence signal of CDKB2;1-GFP was tightly associated with chromosome alignment as well as with spindle structure during the metaphase. During the telophase, the signal was localized to the spindle midzone and the separating sister chromosomes, and then to the phragmoplast. On the other hand, the CycB2;2-GFP fluorescence signal was detected in nuclei during the interphase and prophase, moved to the metaphase chromosomes, and then disappeared completely after the cells passed through the metaphase. Co-localization of CDKB2;1-GFP and CycB2;2-GFP on chromosomes aligned at the center of the metaphase cells suggests that the CDKB2-CycB2 complex may function in retaining chromosomes at the metaphase plate. Overexpression of CycB2;2 in rice plants resulted in acceleration of root growth without any increase in cell size, indicating that CycB2;2 promoted cell division probably through association with CDKB2 in the root meristem.
authors.affiliation: Institute of Molecular and Cellular Biosciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Japan.
authors.forename: Jeongkyung
authors.initials: J
authors.lastname: Lee
authors.forename: Avijit
authors.initials: A
authors.lastname: Das
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Yamaguchi
authors.forename: Junji
authors.initials: J
authors.lastname: Hashimoto
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Tsutsumi
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Uchimiya
authors.forename: Masaaki
authors.initials: M
authors.lastname: Umeda
mesh_terms: D002453:Cell Cycle; D002455:Cell Division; D019926:Cyclin B / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D012275:Oryza / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development; D030821:Plants, Genetically Modified; D011485:Protein Binding; D014026:Nicotiana / Q000235:genetics
chemical_list: D019926:Cyclin B; D018844:Cyclin-Dependent Kinases