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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

β-Subunits of the SnRK1 Complexes Share a Common Ancestral Function Together with Expression and Function Specificities; Physical Interaction with Nitrate Reductase Specifically Occurs via AKINβ1-Subunit^1,[C],[OA]

Laboratoire Signalisation et Régulation Coordonnée du Métabolisme Carboné et Azoté, Institut de Biotechnologie des Plantes (UMR8618), Université Paris-Sud, F–91405 Orsay cedex, France

The SNF1/AMPK/SnRK1 kinases are evolutionary conserved kinases involved in yeast, mammals, and plants in the control of energy balance. These heterotrimeric enzymes are composed of one -type catalytic subunit and two - and β-type regulatory subunits. In yeast it has been proposed that the β-type subunits regulate both the localization of the kinase complexes within the cell and the interaction of the kinases with their targets. In this work, we demonstrate that the three β-type subunits of Arabidopsis (Arabidopsis thaliana; AKINβ1, AKINβ2, and AKINβ3) restore the growth phenotype of the yeast sip1sip2gal83 triple mutant, thus suggesting the conservation of an ancestral function. Expression analyses, using AKINβ promoter::β-glucuronidase transgenic lines, reveal different and specific patterns of expression for each subunit according to organs, developmental stages, and environmental conditions. Finally, our results show that the β-type subunits are involved in the specificity of interaction of the kinase with the cytosolic nitrate reductase. Together with previous cell-free phosphorylation data, they strongly support the proposal that nitrate reductase is a real target of SnRK1 in the physiological context. Altogether our data suggest the conservation of ancestral basic function(s) together with specialized functions for each β-type subunit in plants.

² Present address: Laboratoire de Bioénergétique Fondamentale et Appliquée, INSERM U884, Université Joseph Fourier, F–38041 Grenoble, France.

³ Present address: Laboratoire de Biologie Cellulaire, Laboratoire Commun de Cytologie, INRA Versailles, RD10, Route de Saint Cyr, F–78026 Versailles cedex, France.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Martine Thomas (martine.thomas{at}u-psud.fr).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.123026

^* Corresponding author; e-mail martine.thomas{at}u-psud.fr.

Received May 15, 2008; accepted August 11, 2008; published September 3, 2008.

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