The Arabidopsis thaliana GSK3/Shaggy like kinase AtSK3-2 modulates floral cell expansion.
The GSK3/Shaggy family of serine/threonine protein kinases is involved in a series of biological processes in animals, plants and yeast [Charrier et al. (2002) Plant Physiol 130:577-590; Jope and Johnson (2004) Trends Biochem Sci 29:95-102; Li and Nam (2002) Science 295:1299-1301; Piao et al. (2001) Plant J 27:305-314]. In Arabidopsis thaliana, out of the 10 members of the GSK3/Shaggy-like gene family (AtSKs), a biological function has been assigned to only 1 member (AtSK2-1) by mutation. In the present work, a study was undertaken to elucidate the function of AtSK3-2. We have generated mutated versions of the A. thaliana Shaggy-like kinase 3-2 (AtSK3-2), in which Lys(167) and Arg(178), respectively homologues to Lys(85) and Arg(96) of the mammal GSK3beta, were modified into Ala by site-directed mutagenesis. In vitro kinase activity assays of the mutated recombinant protein AtSK3-2-R178A showed that the "primed activity" of the mutated kinase was reduced by 90% while the "non-primed" activity was only 20% reduced compared to the wild-type protein kinase. However, the mutant protein AtSK3-2-K167A showed no activity. Arabidopsis transgenic lines over-expressing AtSK3-2-R178A displayed smaller floral organs, namely pedicels, sepals and petals. Conversely, over-expression of both the wild-type AtSK3-2 protein and the AtSK3-2-K167A mutated version, displayed no altered morphogenesis. Scanning electron microscopic analyses of the AtSK3-2-R178A transgenic plants clearly showed a reduced cell size in flower organs, in which quantitative RT-PCR expression analyses of cell wall expansion enzymes showed reduced transcript levels of three xyloglucan endotransglycosylases (XET), namely XTH22 (TCH4), XTH23 (XTR6) and XTH30 (XTR4). Our data show that AtSK3-2 plays an important role in the control of cell elongation in flower development.
Claisse
Gaëlle
G
Institut de Biotechnologie des Plantes (IBP), UMR CNRS 8618, Laboratoire de Biologie du Développement des Plantes, Université Paris-Sud XI, Bat 630, Orsay Cedex 91405, France.
Charrier
Bénédicte
B
Kreis
Martin
M
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D049108:Cell Enlargement; D002473:Cell Wall / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D035264:Flowers / Q000166:cytology / Q000201:enzymology / Q000254:growth & development; D038362:Glycogen Synthase Kinase 3; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D016415:Sequence Alignment
D029681:Arabidopsis Proteins; D017346:Protein Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3; C520628:SK3-2 protein, Arabidopsis