title: SIAMESE, a plant-specific cell cycle regulator, controls endoreplication onset in Arabidopsis thaliana.
abstract: Recessive mutations in the SIAMESE (SIM) gene of Arabidopsis thaliana result in multicellular trichomes harboring individual nuclei with a low ploidy level, a phenotype strikingly different from that of wild-type trichomes, which are single cells with a nuclear DNA content of approximately 16C to 32C. These observations suggested that SIM is required to suppress mitosis as part of the switch to endoreplication in trichomes. Here, we demonstrate that SIM encodes a nuclear-localized 14-kD protein containing a cyclin binding motif and a motif found in ICK/KRP (for Interactors of Cdc2 kinase/Kip-related protein) cell cycle inhibitor proteins. Accordingly, SIM was found to associate with D-type cyclins and CDKA;1. Homologs of SIM were detected in other dicots and in monocots but not in mammals or fungi. SIM proteins are expressed throughout the shoot apical meristem, in leaf primordia, and in the elongation zone of the root and are localized to the nucleus. Plants overexpressing SIM are slow-growing and have narrow leaves and enlarged epidermal cells with an increased DNA content resulting from additional endocycles. We hypothesize that SIM encodes a plant-specific CDK inhibitor with a key function in the mitosis-to-endoreplication transition.
authors.affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Churchman
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Brown
authors.forename: Naohiro
authors.initials: N
authors.lastname: Kato
authors.forename: Viktor
authors.initials: V
authors.lastname: Kirik
authors.forename: Martin
authors.initials: M
authors.lastname: Hülskamp
authors.forename: Dirk
authors.initials: D
authors.lastname: Inzé
authors.forename: Lieven
authors.initials: L
authors.lastname: De Veylder
authors.forename: Jason D
authors.initials: JD
authors.lastname: Walker
authors.forename: Zhengui
authors.initials: Z
authors.lastname: Zheng
authors.forename: David G
authors.initials: DG
authors.lastname: Oppenheimer
authors.forename: Taylor
authors.initials: T
authors.lastname: Gwin
authors.forename: Jason
authors.initials: J
authors.lastname: Churchman
authors.forename: John C
authors.initials: JC
authors.lastname: Larkin
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D048429:Cell Size; D019926:Cyclin B / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D004261:DNA Replication; D018744:DNA, Plant / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D015870:Gene Expression; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D008164:Luminescent Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D010641:Phenotype; D018515:Plant Leaves / Q000166:cytology / Q000648:ultrastructure; D011485:Protein Binding; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D018797:Cell Cycle Proteins; C462528:CycB1 protein, Arabidopsis; D019926:Cyclin B; D016213:Cyclins; D018744:DNA, Plant; D008164:Luminescent Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C517317:SIAMESE protein, Arabidopsis; C054562:yellow fluorescent protein, Bacteria; C434472:CDKA1 protein, Arabidopsis; D018844:Cyclin-Dependent Kinases