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Published on February 27, 2008; 10.1104/pp.107.114710

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Received December 7, 2007
Accepted February 20, 2008

OPPP-dependent sugar sensing as a mechanism for regulation of root ion transporters by photosynthesis

Laurence Lejay *, Judith Wirth , Marjorie Pervent , Joanna Marie-France Cross , Pascal Tillard , and Alain Gojon

The Institut de Biologie Integrative des Plantes, UMR 5004, Biochimie et Physiologie Moleculaire des Plantes, Agro-M/CNRS/INRA/SupAgro/UM2, 2 Place Viala, F-34060 Montpellier, France ; The Institut de Biologie Integrative des Plantes, UMR 759, Ecophysiologie des Plantes Sous Stress Environnementaux, Agro-M/INRA/SupAgro, 2 Place Viala, F-34060 Montpellier, France and Max-Planck Institute of Molecular Plant Physiology, Wissenschaftspark Golm, Am Muhlenberg 1 D-14476 Potsdam, Germany

* Corresponding author; email: lejay{at}supagro.inra.fr.

Root ion transport systems are regulated by light and/or sugars, but the signalling mechanisms are unknown. We showed previously that induction of the NRT2.1 NO3- transporter gene by sugars was dependent on carbon metabolism downstream hexokinase (HXK) in glycolysis. To gain further insights on this signalling pathway, and to explore more systematically the mechanisms coordinating root nutrient uptake with photosynthesis, we studied the regulation of 19 light/sugar-induced ion transporter genes. Combination of sugar, sugar analogs, light and CO2 treatments provided evidence that these genes are not regulated by a common mechanism, and unravelled at least four different signalling pathways involved: regulation by light per se, by HXK-dependent sugar sensing, and by sugar sensing upstream or downstream HXK, respectively. More specific investigation of sugar sensing downstream HXK, using NRT2.1 and NRT1.1 NO3- transporter genes as models, highlighted a correlation between expression of these genes and the concentration of glucose-6-P (G6P) in the roots. Furthermore, the phosphogluconate dehydrogenase inhibitor 6-aminonicotinamine (6-AN) almost completely prevented induction of NRT2.1 and NRT1.1 by sucrose, indicating that G6P metabolization within the oxidative pentose phosphate pathway (OPPP) is required for generating the sugar signal. Out of the 19 genes investigated, most of those belonging to NO3-, NH4+ or SO42- transporter families were regulated like NRT2.1 and NRT1.1. These data suggest that a yet unidentified OPPP-dependent sugar sensing pathway governs the regulation of root N and S acquisition by the C status of the plant, to coordinate the availability of these three elements for amino acid synthesis.






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