First published online November 7, 2002; 10.1104/pp.008573
Plant Physiol, December 2002, Vol. 130, pp. 1871-1882
Comparative Molecular and Functional Analyses of the Tobacco
Cyclin-Dependent Kinase Inhibitor NtKIS1a and Its Spliced Variant
NtKIS1b1
Sophie
Jasinski,
Claudette
Perennes,
Catherine
Bergounioux, and
Nathalie
Glab*
Laboratoire Cycle Cellulaire, Institut de Biotechnologie
des Plantes, Centre National de la Recherche Scientifique, Unité
Mixte de Recherche 8618, Université Paris-Sud, 91405 Orsay cedex,
France
In all eukaryotes, cell cycle progression is controlled by
cyclin-dependent kinases (CDKs) whose activity is regulated at several
levels including inhibition by CDK inhibitors. Here, we report a
comparative molecular and functional analysis of the tobacco
(Nicotiana tomentosiformis) CDK inhibitor, NtKIS1a, and its spliced variant, NtKIS1b. The C-terminal end of NtKIS1a shares strong sequence similarity with mammalian CIP/KIP inhibitors, which is
not the case for NtKIS1b. Consistent with this, NtKIS1a but not NtKIS1b
inhibits in vitro the kinase activity of CDK/cyclin complexes, and
tobacco (Nicotiana tabacum) D-type cyclins and an A-type
CDK are NtKIS1a, but not NtKIS1b, interacting partners. Although both
NtKIS1a and NtKIS1b transcripts are mainly found in flowers and more
precisely in stamens, NtKIS1b transcript levels are cell cycle
regulated, whereas those of NtKIS1a remain constant during the cell
cycle. NtKIS1a and NtKIS1b fused to fluorescent proteins are localized
in the nucleus when transiently expressed in onion epidermal cells.
Furthermore, there is no competition for their nuclear localization
when they are simultaneously overexpressed. In vitro competition toward
CDK kinase activity suggests that NtKIS1b is a strong competitor of
NtKIS1a. Arabidopsis plants overexpressing NtKIS1a-green fluorescent
protein (GFP) or NtKIS1b-GFP fusion proteins were obtained. In these
plants, the fusion proteins are still localized in the nucleus.
Interestingly, NtKIS1a-GFP-overexpressing plants display strong
morphological modifications and a reduced CDK kinase activity, whereas
NtKIS1b-GFP-overexpressing plants display a wild-type phenotype
including a wild-type CDK kinase activity. Our results strongly suggest
that the inhibition of the kinase activity is responsible for the
phenotypic modifications.
1
This work was supported by the French
Ministère de l'Education Nationale, de la Recherche, et de la
Technologie (grant to S.J.).
*
Corresponding author; e-mail glab{at}ibp.u-psud.fr; fax 33169153423.
© 2002 American Society of Plant Biologists
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