title: The syncytium-specific expression of the Orysa;KRP3 CDK inhibitor: implication of its involvement in the cell cycle control in the rice (Oryza sativa L.) syncytial endosperm.
abstract: During rice (Oryza sativa L.) seed development, the primary endosperm nucleus undergoes a series of divisions without cytokinesis, producing a multinucleate cell, known as a syncytium. After several rounds of rapid nuclear proliferation, the syncytium ceases to undergo mitosis; thereafter, the syncytium is partitioned into individual cells by a specific type of cytokinesis called cellularization. The transition between syncytium and cellularization is important in determining the final seed size and is a model for studying the cell cycle and cytokinesis. The involvement of cyclin-dependent kinase (CDK) inhibitors (CKIs) in cell cycle control was investigated here during the transition between syncytium and cellularization. It was found that one of the rice CKIs, Orysa;KRP3, is strongly expressed in the caryopsis at 2 d after flowering (DAF), and its expression is significantly reduced at 3 DAF. The other CKI transcripts did not show such a shift at 2 DAF. In situ hybridization analysis revealed that Orysa;KRP3 is expressed in multinucleate syncytial endosperm at 2 DAF, but not in cellularized endosperm at 3 DAF. Two-hybrid assays showed that Orysa;KRP3 binds Orysa;CDKA;1, Orysa;CDKA;2, Orysa;CycA1;1, and Orysa;CycD2;2. By contrast, Orysa;CDKB2;1 and Orysa;CycB2;2 do not show binding to Orysa;KRP3. Orysa;KRP3 was able to rescue yeast premature cell division due to the dominant positive expression of mutant rice CDKA;1 indicating that Orysa;KRP3 inhibited rice CDK. These data suggest that Orysa;KRP3 is involved in cell cycle control of syncytial endosperm.
authors.affiliation: United Graduate School of Agricultural Sciences, Iwate University, 3-18-8, Ueda, Morioka, Iwate 020-8550, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Mizutani
authors.forename: Takuma
authors.initials: T
authors.lastname: Naganuma
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Tsutsumi
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Saitoh
mesh_terms: D002453:Cell Cycle / Q000235:genetics*; D050756:Cyclin-Dependent Kinase Inhibitor Proteins / Q000235:genetics* / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D016213:Cyclins / Q000378:metabolism; D056625:Endosperm / Q000166:cytology* / Q000235:genetics / Q000254:growth & development; D035264:Flowers / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D015726:Giant Cells / Q000166:cytology / Q000378:metabolism*; D009928:Organ Specificity / Q000235:genetics; D012275:Oryza / Q000033:anatomy & histology / Q000166:cytology / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology
chemical_list: D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D016213:Cyclins; D010940:Plant Proteins; D012333:RNA, Messenger; D018844:Cyclin-Dependent Kinases