A 60 kDa COX1 protein in mitochondria of carrot irrespective of the presence of C-terminal extensions in the cox1 reading frames

Polymorphic minisatellites in the mitochondrial DNAs of Oryza and Brassica

Polymorphic analyses of angiosperm mitochondrial DNA are rare in comparison with chloroplast DNA, because few target sequences in angiosperm mitochondrial DNA are known. Minisatellites, a tandem array of repeated sequences with a repeat unit of 10 to ~100 bp, are popular target sequences of animal mitochondria, but Beta vulgaris is the only known angiosperm species for which such an analysis has been conducted. From this lack of information, it was uncertain as to whether polymorphic minisatellites existed in other angiosperm species. Ten plant mitochondrial DNAs were found to contain minisatellite-like repeated sequences, most of which were located in intergenic regions but a few occurred in gene coding and intronic regions. Oryza and Brassica accessions were selected as models for the investigation of minisatellite polymorphism because substantial systematic information existed. PCR analysis of 42 Oryza accessions revealed length polymorphisms in four of the five minisatellites. The mitochondrial haplotypes of the 16 Oryza accessions with chromosomal complement (genome) types of CC, BBCC and CCDD were identical but were clearly distinguished from BB-genome accessions, a result consistent with the notion that the cytoplasmic donor parent of the amphidiploid species might be the CC-genome species. Twenty-nine accessions of six major cultivated species of Brassica were classified into five mitochondrial haplotypes based on two polymorphic minisatellites out of six loci. The haplotypes of Brassica juncea and Brassica carinata accessions were identical to Brassica rapa and Brassica nigra accessions, respectively. The haplotypes of Brassica napus accessions were heterogeneous and unique, results that were consistent with previous studies.

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

The angiosperm mitochondrial genome is the largest and least gene-dense among the eukaryotes, because its intergenic regions are expanded. There seems to be no functional constraint on the size of the intergenic regions; angiosperms maintain the large mitochondrial genome size by a currently unknown mechanism. After a brief description of the angiosperm mitochondrial genome, this review focuses on our current knowledge of the mechanisms that control the maintenance and alteration of the genome. In both processes, the control of homologous recombination is crucial in terms of site and frequency. The copy numbers of various types of mitochondrial DNA molecules may also be controlled, especially during transmission of the mitochondrial genome from one generation to the next. An important characteristic of angiosperm mitochondria is that they contain polypeptides that are translated from open reading frames created as byproducts of genome alteration and that are generally nonfunctional. Such polypeptides have potential to evolve into functional ones responsible for mitochondrially encoded traits such as cytoplasmic male sterility or may be remnants of the former functional polypeptides.

A mitochondrial gene involved in cytochrome c maturation (ccmC) is expressed as a precursor with a long NH2-terminal extension in sugar beet

Extensive genome rearrangement is one of the major mechanisms of angiosperm mitochondrial evolution. As a by-product, some angiosperm mitochondrial genes exhibit divergent organization, but not all of these genes have been fully characterized. Sugar beet ccmC, which plays an important role in cytochrome c maturation, harbors a unique extended NH(2) terminal region of 277 amino acid residues (N-extension) instead of a conserved translational initiation codon. The 5' termini of two major RNA species were determined by primer extension analysis, which revealed that the larger transcript covered the entire N-extension. Nucleotide sequencing of the cDNA revealed that a total of 31 C-to-U RNA editing events occurred in the N-extension and the ccmC-homologous region (ccmC-core region), resulting in improvement of amino acid sequence conservation. Antiserum was raised against a synthetic peptide corresponding to the ccmC-core region and was used for protein gel blot analysis of sugar beet and radish mitochondrial proteins. The detected 29.5-kDa signal band is shared by sugar beet and radish. Two additional larger signal bands are exclusively detected from sugar beet. The largest signal band is also detected by anti-N-extension antiserum. Our results indicate that sugar beet ccmC is translated as a long precursor with N-extension.

Petaloid-type cms in carrot is not associated with expression of atp8 (orfB)

Two different atp8 reading frames with divergent C-terminal extensions were identified in a sterility-inducing mitochondrial type (mitotype) of carrot; examination of three fertility-inducing mitotypes revealed atp8 reading frames that were either terminated at a position conserved among other plant atp8 genes or continued with unique C-terminal extensions. Similarities between the C-terminal extensions suggest ancient common ancestry, but the level of sequence divergence implies lack of functional conservation. Northern analysis indicated that the C-terminal extensions are transcribed and are present within the primary atp8 transcripts. Western analysis revealed that the products of the two extended atp8 reading frames encoded by the sterility-inducing mitotype are significantly smaller than those predicted by complete translation of their C-terminal extensions, but are slightly larger than the products from unextended reading frames. No alterations were observed in atp8 transcripts or proteins isolated from flowers of the sterility-inducing mitotype that were phenotypically fertile as a result of segregation for nuclear fertility-restoring Ms or Rf alleles, and thus, there is no evidence that expression of atp8 is directly involved in the petaloid cms phenotype in carrot.