First published online October 3, 2002; 10.1104/pp.004564
Plant Physiol, October 2002, Vol. 130, pp. 657-665
The KNAT2 Homeodomain Protein Interacts with Ethylene and
Cytokinin Signaling1
Olivier
Hamant,
Fabien
Nogué,
Enric
Belles-Boix,
Delphine
Jublot,
Olivier
Grandjean,
Jan
Traas, and
Véronique
Pautot*
Laboratoire de Biologie Cellulaire (O.H., E.B.-B., D.J., J.T.,
V.P.) and Station de Génétique et d'Amélioration des
Plantes (F.N., O.G.), Institut National de la Recherche Agronomique,
Route de St. Cyr, 78026 Versailles cedex, France
Using a transgenic line that overexpresses a fusion of the
KNAT2 (KNOTTED-like Arabidopsis) homeodomain protein and the
hormone-binding domain of the glucocorticoid receptor (GR), we have
investigated the possible relations between KNAT2 and
various hormones. Upon activation of the KNAT2-GR fusion, we observed a
delayed senescence of the leaves and a higher rate of shoot initiation,
two processes that are also induced by cytokinins and inhibited by
ethylene. Furthermore, the activation of the KNAT2-GR fusion induced
lobing of the leaves. This feature was partially suppressed by
treatment with the ethylene precursor 1-aminocyclopropane-1-carboxylic
acid, or by the constitutive ethylene response ctr1
mutation. Conversely, some phenotypic traits of the ctr1
mutant were suppressed by the activation of the KNAT2-GR fusion. These
data suggest that KNAT2 acts synergistically with
cytokinins and antagonistically with ethylene. In the shoot apical
meristem, the KNAT2 gene is expressed in the L3 layer
and the rib zone. 1-Aminocyclopropane-1-carboxylic acid treatment
restricted the KNAT2 expression domain in the shoot apical meristem and reduced the number of cells in the L3. The latter
effect was suppressed by the activation of the KNAT2-GR construct.
Conversely, the KNAT2 gene expression domain was
enlarged in the ethylene-resistant etr1-1 mutant or in
response to cytokinin treatment. These data suggest that ethylene and
cytokinins act antagonistically in the meristem via KNAT2 to regulate
the meristem activity.
1
This work was supported by the Ministère
de l'Enseignement Supérieur et de la Recherche and by the
European Union Regulatory Gene Initiative In Arabidopsis program
(to E.B.-B.).
*
Corresponding author; e-mail pautot{at}versailles.inra.fr; fax
33-1-30-83-30-99.
© 2002 American Society of Plant Physiologists
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