title: Arabidopsis S6 kinase mutants display chromosome instability and altered RBR1-E2F pathway activity.
abstract: The 40S ribosomal protein S6 kinase (S6K) is a conserved component of signalling pathways controlling growth in eukaryotes. To study S6K function in plants, we isolated single- and double-knockout mutations and RNA-interference (RNAi)-silencing lines in the linked Arabidopsis S6K1 and S6K2 genes. Hemizygous s6k1s6k2/++ mutant and S6K1 RNAi lines show high phenotypic instability with variation in size, increased trichome branching, produce non-viable pollen and high levels of aborted seeds. Analysis of their DNA content by flow cytometry, as well as chromosome counting using DAPI staining and fluorescence in situ hybridization, revealed an increase in ploidy and aneuploidy. In agreement with this data, we found that S6K1 associates with the Retinoblastoma-related 1 (RBR1)-E2FB complex and this is partly mediated by its N-terminal LVxCxE motif. Moreover, the S6K1-RBR1 association regulates RBR1 nuclear localization, as well as E2F-dependent expression of cell cycle genes. Arabidopsis cells grown under nutrient-limiting conditions require S6K for repression of cell proliferation. The data suggest a new function for plant S6K as a repressor of cell proliferation and required for maintenance of chromosome stability and ploidy levels.
authors.affiliation: Royal Holloway, University of London, School of Biological Sciences, Egham Hill, Egham, UK. rhenriques@mail.rockefeller.edu
authors.forename: Rossana
authors.initials: R
authors.lastname: Henriques
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Magyar
authors.forename: Antonia
authors.initials: A
authors.lastname: Monardes
authors.forename: Safina
authors.initials: S
authors.lastname: Khan
authors.forename: Christine
authors.initials: C
authors.lastname: Zalejski
authors.forename: Juan
authors.initials: J
authors.lastname: Orellana
authors.forename: László
authors.initials: L
authors.lastname: Szabados
authors.forename: Consuelo
authors.initials: C
authors.lastname: de la Torre
authors.forename: Csaba
authors.initials: C
authors.lastname: Koncz
authors.forename: László
authors.initials: L
authors.lastname: Bögre
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D043171:Chromosomal Instability; D018744:DNA, Plant / Q000032:analysis; D050684:E2F Transcription Factors / Q000378:metabolism*; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000494:pharmacology; D055786:Gene Knockout Techniques; D017404:In Situ Hybridization, Fluorescence; D007211:Indoles / Q000494:pharmacology; D011003:Ploidies; D011485:Protein Binding; D025941:Protein Interaction Mapping; D019893:Ribosomal Protein S6 Kinases / Q000235:genetics* / Q000378:metabolism; D013194:Staining and Labeling
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; D050684:E2F Transcription Factors; D005456:Fluorescent Dyes; D007211:Indoles; C487568:RBR1 protein, Arabidopsis; C007293:DAPI; D019893:Ribosomal Protein S6 Kinases