title: Analyses of two rice (Oryza sativa) cyclin-dependent kinase inhibitors and effects of transgenic expression of OsiICK6 on plant growth and development.
abstract: OBJECTIVE
  Plants have a family of proteins referred to as ICKs (inhibitors of cyclin-dependent kinase, CDK) or KRPs (Kip-related proteins) that function to regulate the activities of CDK. Knowledge of these plant CDK inhibitors has been gained mostly from studies of selected members in dicotyledonous plants, particularly Arabidopsis. Much remains to be learned regarding the differences among various members of the ICK/KRP family, and regarding the function and regulation of these proteins in monocotyledonous plants.
  
  
  METHODS
  We analysed ICK-related sequences in the rice (Orysa sativa L. subsp. indica) genome and determined that there are six members with the conserved C-terminal signature region for ICK/KRP proteins. They are referred to as OsiICKs and further analyses were performed. The interactions with CDKs and cyclins were determined by a yeast two-hybrid assay, and cellular localization by fusion with the enhanced green fluorescence protein (EGFP). The expression of OsiICK6 in different tissues and in response to several treatments was analysed by reverse transcriptase-mediated polymerase chain reaction (RT-PCR) and real-time PCR. Furthermore, OsiICK6 was over-expressed in transgenic rice plants and significant phenotypes were observed.
  
  
  CONCLUSIONS
  Based on putative protein sequences, the six OsiICKs are grouped into two classes, with OsiICK1 and OsiICK6 in each of the two classes, respectively. Results showed that OsiICK1 and OsiICK6 interacted with OsCYCD, but differed in their interactions with CDKA. Both EGFP:OsiICK1 and EGFP:OsiICK6 were localized in the nucleus. Whereas EGFP:OsiICK6 showed a punctuate subnuclear distribution, OsiICK1 had a homogeneous pattern. Over-expression of OsiICK6 resulted in multiple phenotypic effects on plant growth, morphology, pollen viability and seed setting. In OsiICK6-over-expressing plants, leaves rolled toward the abaxial side, suggesting that cell proliferation is critical in maintaining an even growth along the dorsal-ventral plane of leaf blades.
authors.affiliation: Institute of Crop Science, College of Agriculture and Biotechnology, Zhejiang University, Kaixuan Road 268, Hangzhou, China.
authors.forename: Ruifang
authors.initials: R
authors.lastname: Yang
authors.forename: Qicai
authors.initials: Q
authors.lastname: Tang
authors.forename: Huimei
authors.initials: H
authors.lastname: Wang
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Zhang
authors.forename: Gang
authors.initials: G
authors.lastname: Pan
authors.forename: Hong
authors.initials: H
authors.lastname: Wang
authors.forename: Jumin
authors.initials: J
authors.lastname: Tu
mesh_terms: D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000378:metabolism; D050756:Cyclin-Dependent Kinase Inhibitor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics* / Q000254:growth & development*; D010802:Phylogeny; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011485:Protein Binding; D021381:Protein Transport; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012639:Seeds / Q000254:growth & development / Q000378:metabolism; D020539:Sequence Analysis, Protein; D013312:Stress, Physiological; D014026:Nicotiana / Q000166:cytology
chemical_list: D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D016213:Cyclins; D010940:Plant Proteins; D018844:Cyclin-Dependent Kinases