The Ogura sterility-inducing protein forms a large complex without interfering with the oxidative phosphorylation components in rapeseed mitochondria

Abstract

The Ogura cytoplasmic male sterility causing protein, ORF138, was found to be part of a complex with an apparent size of over 750 kDa in the inner membrane of mitochondria of sterile plants. ORF138 did not colocalize with any of the oxidative phosphorylation complexes, nor did its presence modify their apparent size or amount, compared to samples from fertile isogenic plants. We attempted to detect potential proteins or nucleic acids that could be involved in the large ORF138 complex by 2D PAGE, immunoprecipitation and nuclease treatments of native extracts. All our results suggest that the ORF138 protein is the main, if not only, component of this large complex. The capacities of complexes I, II, IV, and ATP synthase were identical in samples from sterile and fertile plants. Isolated mitochondria from sterile plants showed a higher oxygen consumption than those from fertile plants. In vivo respiration measurements suggest that the difference in O(2) consumption measured at the organelle level is compensated at the cell/tissue level, completely in leaves, but only partially in male reproductive organs.

Cost of Having the Largest Mitochondrial Genome: Evolutionary Mechanism of Plant Mitochondrial Genome

“…Microorganisms such as E coli can also be used as hosts to examine the toxin sensitivities conferred by specific ORFs [36,76]. It is known that the polypeptides encoded by maize urf13-T, radish orf138 (associated with CMS), and sugar beet preSatp6 form oligomers in the inner membrane [36,83,106], which may function as ionophores [107]. However, sugar beet ORF129, which also causes CMS when targeted to the mitochondria, shows a different localization pattern [101].…”

Alterations of Mitochondrial Protein Assembly and Jasmonic Acid Biosynthesis Pathway in Honglian (HL)-type Cytoplasmic Male Sterility Rice

“…Another CMS protein, ORF138 in rapeseed, was found as part of a 750-kDa complex but not associated with a wide range of complexes (7). A previous study showed that the membrane potential is decreased in YtA (13).…”

“…Studies using mitochondria isolated from vegetative tissues that constitutively express CMS-associated proteins are therefore an excellent system to study the mechanism of aborted pollen development (7,32,33). In this study, a quantitative proteomics approach was used to compare intact mitochondrial proteins and mitochondrial protein complexes between the HL-type CMS rice YtA and its isogenic fertile line YtB.…”

“…Based on our proteomics results, many well known protein complexes were identified from BN1 to BN4 fractions, including the prohibitin (PHB) complex, complex I, the heat shock protein (HSP) complex, complex V, complex III 2 , and the F 1 part of complex V (7,19,25). It was possible that ORFH79 was co-localized with these complexes.…”

“…The first is the "gain-of-function" theory, which is supported by the finding that T-URF13, an inner mitochondrial membrane protein, may form a pore and interfere with membrane activity in the cytoplasm of maize (5,6). In addition, ORF138, which forms a complex of over 750 kDa, has been proposed to act as a pore in the inner mitochondrial membrane in a sterile line of rapeseed (7). The second theory, the "loss-of-function" theory, is supported by the characterization of ORF522, which shares a similar N-terminal amino acid sequence with ORFB but competes with ORFB in binding to the ATP synthase (complex V) subunit in sunflowers to reduce the stability and efficiency of this complex (8).…”