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Free keywords:
TCA cycle, pyruvate dehydrogenase phosphorylation, mitochondrial protein phosphatase, TCA cycle enzymes phosphorylation
Abstract:
Protein phosphorylation is a well-established post-translational mechanism that regulates protein functions and metabolic pathways. It is known that several plant mitochondrial proteins are phosphorylated in a reversible manner. However, the identity of the protein kinases/phosphatases involved in this mechanism and their role in the regulation of the TCA cycle remain unclear. Here, we isolated and characterized plants lacking two mitochondrially targeted phosphatases (Sal2 and PP2c63) alongside pyruvate dehydrogenase kinase (PDK). Protein-protein interaction analysis, quantitative phosphoproteomics, and enzymatic analyses revealed that PDK specifically regulates pyruvate dehydrogenase complex (PDC), while PP2c63 nonspecifically regulates PDC. Recombinant PP2c63 and Sal2 proteins were added to mitochondria isolated from mutant plants and protein-protein interaction and enzymatic analyses were performed. The results indicate that PP2c63 directly phosphorylates and modulates the activity of PDC, while Sal2 only indirectly affects TCA cycle enzymes. Characterization of steady-state metabolite levels and fluxes in the described mutant lines also revealed that these phosphatases regulate flux through the TCA cycle, and that altered metabolism in the sal2 pp2c63 double mutant compromises growth. These results are discussed in the context of current models of the control of respiration in plants.
