Cox2A/Cox2B subunit interaction in Polytomella sp. cytochrome c oxidase: role of the Cox2B subunit extension

New Dielis species and structural dichotomy of the mitochondrial cox2 gene in Scoliidae wasps

Some mitochondrial protein-coding genes of protists and land plants have split over the course of evolution into complementary genes whose products can form heteromeric complexes that likely substitute for the undivided proteins. One of these genes, cox2, has also been found to have split in animals, specifically in Scoliidae wasps (Hymenoptera: Apocrita) of the genus Dielis (Campsomerini), while maintaining the conventional structure in related Scolia (Scoliini). Here, a hitherto unrecognized Nearctic species of Dielis, D. tejensis, is described based on its phenotype and mtDNA. The mitogenome of D. tejensis sp. nov. differs from that of the sympatric sibling species Dielis plumipes fossulana by the reduced size of the cox2-dividing insert, which, however, still constitutes the fifth part of the mtDNA; an enlarged nad2-trnW intergenic region; the presence of two trnK^ttt paralogues; and other features. Both species of Dielis have a unique insertion of a threonine in COXIIA, predicted to be involved in COXIIA-COXIIB docking, and substitutions of two hydrophobic residues with redox-active cysteines around the Cu_A centre in COXIIB. Importantly, the analysis of mtDNA from another Campsomerini genus, Megacampsomeris, shows that its cox2 gene is also split. The presented data highlight evolutionary processes taking place in hymenopteran mitogenomes that do not fall within the mainstream of animal mitochondrion evolution.

Plant Mitochondrial Inner Membrane Protein Insertion

During the biogenesis of the mitochondrial inner membrane, most nuclear-encoded inner membrane proteins are laterally released into the membrane by the TIM23 and the TIM22 machinery during their import into mitochondria. A subset of nuclear-encoded mitochondrial inner membrane proteins and all the mitochondrial-encoded inner membrane proteins use the Oxa machinery-which is evolutionarily conserved from the endosymbiotic bacterial ancestor of mitochondria-for membrane insertion. Compared to the mitochondria from other eukaryotes, plant mitochondria have several unique features, such as a larger genome and a branched electron transport pathway, and are also involved in additional cellular functions such as photorespiration and stress perception. This review focuses on the unique aspects of plant mitochondrial inner membrane protein insertion machinery, which differs from that in yeast and humans, and includes a case study on the biogenesis of Cox2 in yeast, humans, two plant species, and an algal species to highlight lineage-specific similarities and differences. Interestingly, unlike mitochondria of other eukaryotes but similar to bacteria and chloroplasts, plant mitochondria appear to use the Tat machinery for membrane insertion of the Rieske Fe/S protein.