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The non-photorespiratory H2-protein is essential for plant growth
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International audience. The glycine decarboxylase is a key mitochondrial protein complex involved in the conversion of glycine to serine. It is constituted of four proteins including three enzymes designated as P-protein (a glycine decarboxylase per se), T-protein (an aminomethyl-transferase), L-protein (a dihydrolipoamide dehydrogenase) and a carrier lipoic acid-dependent protein named H-protein. Arabidopsis contains 3 isoforms of H-proteins, H1, H2 and H3. We aimed at delineating the role of H2 isoform. To do so, we have successfully isolated two independent T-DNA insertion mutants, h2-1 and h2-2. Both lines were knockouts, and exhibited a drastic growth alteration even under non-photorespiratory conditions. Although the three H isoforms differ slightly in their amino sequence, both constitutive and promoter specific expression of H1 and H3 could fully rescue the dwarf phenotype of the h2 mutant, thus supporting a similar functionality between all three isoforms. To explain the impeded growth observed in h2, we carried out a set of analyses aiming at identifying the metabolic consequences of such mutation. The lack of H2 leads to a decrease of the TCA intermediates, and in turn to an alteration of the glycolytic and OxPPP pathways. Our results show that this metabolic congestion of the primary metabolism leads to an accumulation of T6P, a metabolite known to repress the bZIP11/SnRK1 growth activation module. Altogether, this work demonstrates that H2 is essential for plant growth since its metabolic function cannot be compensated by the other photorespiratory isoforms.
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