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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Regulation of One-Carbon Metabolism in Arabidopsis: The N-Terminal Regulatory Domain of Cystathionine -Synthase Is Cleaved in Response to Folate Starvation^1,[W]

Laboratoire de Physiologie Cellulaire Végétale, Unité Mixte de Recherche 5168 Centre National de la Recherche Scientifique-Commissariat à l'Energie Atomique-Institut National de la Recherche Agronomique-Université Joseph Fourier Grenoble I, Institut de Recherches en Technologies et Sciences pour le Vivant, Commissariat à l'Energie Atomique-Grenoble, F–38054 Grenoble cedex 9, France (K.L., B.G., G.C., S.J., F.R., S.R.); and Laboratory of Toxicology (G.-F.Z., W.E.L.) and Unit Plant Hormone Signaling and Bio-imaging, Department of Molecular Genetics (D.V.D.S.), Ghent University, B–9000 Ghent, Belgium

In all organisms, control of folate homeostasis is of vital importance to sustain the demand for one-carbon (C1) units that are essential in major metabolic pathways. In this study we induced folate deficiency in Arabidopsis (Arabidopsis thaliana) cells by using two antifolate inhibitors. This treatment triggered a rapid and important decrease in the pool of folates with significant modification in the distribution of C1-substituted folate coenzymes, suggesting an adaptive response to favor a preferential shuttling of the flux of C1 units to the synthesis of nucleotides over the synthesis of methionine (Met). Metabolic profiling of folate-deficient cells indicated important perturbation of the activated methyl cycle because of the impairment of Met synthases that are deprived of their substrate 5-methyl-tetrahydrofolate. Intriguingly, S-adenosyl-Met and Met pools declined during the initial period of folate starvation but were further restored to typical levels. Reestablishment of Met and S-adenosyl-Met homeostasis was concomitant with a previously unknown posttranslational modification that consists in the removal of 92 amino acids at the N terminus of cystathionine -synthase (CGS), the first specific enzyme for Met synthesis. Rescue experiments and analysis of different stresses indicated that CGS processing is specifically associated with perturbation of the folates pool. Also, CGS processing involves chloroplastic serine-type proteases that are expressed in various plant species subjected to folate starvation. We suggest that a metabolic effector, to date unidentified, can modulate CGS activity in vivo through an interaction with the N-terminal domain of the enzyme and that removal of this domain can suppress this regulation.

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: Stéphane Ravanel (sravanel{at}cea.fr).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.105379

^* Corresponding author; e-mail sravanel{at}cea.fr.

Received July 12, 2007; accepted August 20, 2007; published August 24, 2007.