title: Downregulation of multiple CDK inhibitor ICK/KRP genes upregulates the E2F pathway and increases cell proliferation, and organ and seed sizes in Arabidopsis.
abstract: The ICK/KRP cyclin-dependent kinase (CDK) inhibitors are important plant cell cycle factors sharing only limited similarity with the metazoan CIP/KIP family of CDK inhibitors. Little is known about the specific functions of different ICK/KRP genes in planta. In this study, we created double and multiple mutants from five single Arabidopsis ICK/KRP T-DNA mutants, and used a set of 20 lines for the functional investigation of the important gene family. There were gradual increases in CDK activity from single to multiple mutants, indicating that ICK/KRPs act as CDK inhibitors under normal physiological conditions in plants. Whereas lower-order mutants showed no morphological phenotypes, the ick1 ick2 ick6 ick7 and ick1 ick2 ick5 ick6 ick7 mutants had a slightly altered leaf shape. The quintuple mutant had larger cotyledons, leaves, petals and seeds than the wild-type control. At the cellular level, the ICK/KRP mutants had more but smaller cells in all the organs examined. These phenotypic effects became more apparent as more ICK/KRPs were downregulated, suggesting that to a large extent ICK/KRPs function in plants redundantly in a dosage-dependent manner. Analyses also revealed increased expression of E2F-dependent genes, and elevated RBR1 as well as an increased level of phospho-RBB1 protein in the quintuple mutant. Thus, downregulation of multiple ICK/KRP genes increases CDK activity, upregulates the E2F pathway and stimulates cell proliferation, resulting in increased cell numbers, and larger organs and seeds.
authors: National Key Laboratory of Crop Genetic Improvement, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China.
authors: Yan
authors: Y
authors: Cheng
authors: Ling
authors: L
authors: Cao
authors: Sheng
authors: S
authors: Wang
authors: Yongpeng
authors: Y
authors: Li
authors: Xianzong
authors: X
authors: Shi
authors: Han
authors: H
authors: Liu
authors: Lixia
authors: L
authors: Li
authors: Zhengli
authors: Z
authors: Zhang
authors: Larry C
authors: LC
authors: Fowke
authors: Hong
authors: H
authors: Wang
authors: Yongming
authors: Y
authors: Zhou
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002452:Cell Count; D049109:Cell Proliferation; D048429:Cell Size; D018548:Cotyledon / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D050756:Cyclin-Dependent Kinase Inhibitor Proteins / Q000235:genetics* / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D035264:Flowers / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008954:Models, Biological; D016254:Mutagenesis, Insertional; D010641:Phenotype; D018515:Plant Leaves / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D030821:Plants, Genetically Modified; D012639:Seeds / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; C487568:RBR1 protein, Arabidopsis; D018844:Cyclin-Dependent Kinases
keywords: RBR1 and E2F; cell cycle; cell size; cyclin-dependent kinase inhibitor; plant growth; seed size