Mutations in the three Arabidopsis genes that encode the E2 subunit of the mitochondrial pyruvate dehydrogenase complex differentially affect enzymatic activity and plant growth

Three members of the E2 subunit of the Arabidopsis mitochondrial pyruvate dehydrogenase (mtPDC) complex differentially affect mtPDC activity and plant growth. In all organisms, the mitochondrial pyruvate dehydrogenase complex (mtPDC) consists of three components: E1, E2, and E3. In this multi-enzyme complex, the E2 subunits form the core structure. In Arabidopsis, the E2 subunits are encoded by three genes: mtE2-1, mtE2-2, and mtE2-3. The contribution of each mtE2 gene to total mtPDC activity, however, is unknown. In this study, we show that knockdown of the expression of the mtE2-1 gene to 17 % of that in the wild type has only a slight effect on plant growth whereas knockout of mtE2-2 leads to an embryo-lethal phenotype. The nearly null mutation of mtE2-3 does not cause any developmental abnormality. Based on these results, we conclude that mtE2-2 plays a major role in determining the total activity of the mtPDC in Arabidopsis while mtE2-1 and mtE2-3 are more or less functionally redundant with mtE2-2 under normal growth condition. Our results provide genetic evidence for a recently proposed novel mechanism that regulates plant mtPDC activity.