title: Phosphorylation of p27(KIP1) homologs KRP6 and 7 by SNF1-related protein kinase-1 links plant energy homeostasis and cell proliferation.
abstract: SNF1-related protein kinase-1 (SnRK1), the plant kinase homolog of mammalian AMP-activated protein kinase (AMPK), is a sensor that maintains cellular energy homeostasis via control of anabolism/catabolism balance. AMPK-dependent phosphorylation of p27(KIP1) affects cell-cycle progression, autophagy and apoptosis. Here, we show that SnRK1 phosphorylates the Arabidopsis thaliana cyclin-dependent kinase inhibitor p27(KIP1) homologs AtKRP6 and AtKRP7, thus extending the role of this kinase to regulation of cell-cycle progression. AtKRP6 and 7 were phosphorylated in vitro by a recombinant activated catalytic subunit of SnRK1 (AtSnRK1α1). Tandem mass spectrometry and site-specific mutagenesis identified Thr152 and Thr151 as the phosphorylated residues on AtKRP6- and AtKRP7, respectively. AtSnRK1 physically interacts with AtKRP6 in the nucleus of transformed BY-2 tobacco protoplasts, but, in contrast to mammals, the AtKRP6 Thr152 phosphorylation state alone did not modify its nuclear localization. Using a heterologous yeast system, consisting of a cdc28 yeast mutant complemented by A. thaliana CDKA;1, cell proliferation was shown to be abolished by AtKRP6(WT) and by the non-phosphorylatable form AtKRP6(T152A) , but not by the phosphorylation-mimetic form AtKRP6(T152D). Moreover, A. thaliana SnRK1α1/KRP6 double over-expressor plants showed an attenuated AtKRP6-associated phenotype (strongly serrated leaves and inability to undergo callogenesis). Furthermore, this severe phenotype was not observed in AtKRP6(T152D) over-expressor plants. Overall, these results establish that the energy sensor AtSnRK1 plays a cardinal role in the control of cell proliferation in A. thaliana plants through inhibition of AtKRP6 biological function by phosphorylation.
authors.affiliation: Institut de Biologie des Plantes, Centre National de la Recherche Scientifique Unité Mixte de Recherche 8618, Bâtiment 630, Université Paris-Sud, Saclay Plant Sciences, Orsay Cedex 91405, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Guérinier
authors.forename: Laurine
authors.initials: L
authors.lastname: Millan
authors.forename: Pierre
authors.initials: P
authors.lastname: Crozet
authors.forename: Céline
authors.initials: C
authors.lastname: Oury
authors.forename: François
authors.initials: F
authors.lastname: Rey
authors.forename: Benoit
authors.initials: B
authors.lastname: Valot
authors.forename: Chantal
authors.initials: C
authors.lastname: Mathieu
authors.forename: Jean
authors.initials: J
authors.lastname: Vidal
authors.forename: Michael
authors.initials: M
authors.lastname: Hodges
authors.forename: Martine
authors.initials: M
authors.lastname: Thomas
authors.forename: Nathalie
authors.initials: N
authors.lastname: Glab
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D049109:Cell Proliferation; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D004734:Energy Metabolism; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013912:Threonine / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D013912:Threonine; C436291:CDKN1B protein, human; C587773:KRP6 protein, Arabidopsis; C587774:KRP7 protein, Arabidopsis; C531469:At3g01090 protein, Arabidopsis
keywords: Arabidopsis thaliana; Kip-related protein; SNF1-related protein kinase-1; cell proliferation; energy homeostasis; phosphorylation