RESUMO
KEY MESSAGE: The functional absence of the electron-transfer flavoprotein: ubiquinone oxidoreductase (ETFQO) directly impacts electrons donation to the mitochondrial electron transport chain under carbohydrate-limiting conditions without major impacts on the respiration of cell cultures. Alternative substrates (e.g., amino acids) can directly feed electrons into the mitochondrial electron transport chain (mETC) via the electron transfer flavoprotein/electron-transfer flavoprotein: ubiquinone oxidoreductase (ETF/ETFQO) complex, which supports plant respiration during stress situations. By using a cell culture system, here we investigated the responses of Arabidopsis thaliana mutants deficient in the expression of ETFQO (etfqo-1) following carbon limitation and supplied with amino acids. Our results demonstrate that isovaleryl-CoA dehydrogenase (IVDH) activity was induced during carbon limitation only in wild-type and that these changes occurred concomit with enhanced protein content. By contrast, neither the activity nor the total amount of IVDH was altered in etfqo-1 mutants. We also demonstrate that the activities of mitochondrial complexes in etfqo-1 mutants, display a similar pattern as in wild-type cells. Our findings suggest that the defect of ETFQO protein culminates with an impaired functioning of the IVDH, since no induction of IVDH activity was observed. However, the functional absence of the ETFQO seems not to cause major impacts on plant respiration under carbon limiting conditions, most likely due to other alternative electron entry pathways.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Flavoproteínas Transferidoras de Elétrons , Aminoácidos de Cadeia Ramificada/farmacologia , Arabidopsis/citologia , Arabidopsis/efeitos dos fármacos , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Metabolismo dos Carboidratos , Técnicas de Cultura de Células , Complexo IV da Cadeia de Transporte de Elétrons/genética , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Flavoproteínas Transferidoras de Elétrons/genética , Flavoproteínas Transferidoras de Elétrons/metabolismo , Regulação da Expressão Gênica de Plantas , Isovaleril-CoA Desidrogenase/genética , Isovaleril-CoA Desidrogenase/metabolismo , Mitocôndrias/genética , Mitocôndrias/metabolismo , MutaçãoRESUMO
Plant respiration mostly depends on the activity of glycolysis and the oxidation of organic acids in the tricarboxylic acid cycle to synthesize ATP. However, during stress situations plant cells also use amino acids as alternative substrates to donate electrons through the electron-transfer flavoprotein (ETF)/ETF:ubiquinone oxidoreductase (ETF/ETFQO) complex to the mitochondrial electron transport chain (mETC). Given this, we investigated changes of the oxidative phosphorylation (OXPHOS) system in Arabidopsis thaliana cell culture under carbohydrate starvation supplied with a range of amino acids. Induction of isovaleryl-CoA dehydrogenase (IVDH) activity was observed under carbohydrate starvation which was associated with increased amounts of IVDH protein detected by immunoblotting. Furthermore, activities of the protein complexes of the mETC were reduced under carbohydrate starvation. We also observed that OXPHOS system activity behavior is differently affected by different amino acids and that proteins associated with amino acids catabolism are upregulated in cells following carbohydrate starvation. Collectively, our results support the contention that ETF/ETFQO is an essential pathway to donate electrons to the mETC and that amino acids are alternative substrates to maintain respiration under carbohydrate starvation.