Characterization of the Brassica campestris mitochondrial gene for subunit six of NADH dehydrogenase: nad6 is present in the mitochondrion of a wide range of flowering plants

Lupin nad 9 and nad 6 genes and their expression: 5′ termini of the nad 9 gene transcripts differentiate lupin species

The mitochondrial nad9 and nad6 genes were analyzed in four lupin species: Lupinus luteus, Lupinus angustifolius, Lupinus albus and Lupinus mutabilis. The nucleotide sequence of these genes confirmed their high conservation, however, higher number of nucleotide substitution was observed in the L. albus genes. Southern hybridizations confirmed the presence of single copy number of these genes in L. luteus, L. albus and L. angustifolius. The expression of nad9 and nad6 genes was analyzed by Northern in different tissue types of analyzed lupin species. Transcription analyses of the two nad genes displayed single predominant mRNA species of about 0.6 kb in L. luteus and L. angustifolius. The L. albus transcripts were larger in size. The nad9 and nad6 transcripts were modified by RNA editing at 8 and 11 positions, in L. luteus and L. angustifolius, respectively. The gene order, rps3-rpl16-nad9, found in Arabidopsis thaliana is also conserved in L. luteus and L. angustifolius mitochondria. L. luteus and L. angustifolius showed some variability in the sequence of the nad9 promoter region. The last feature along with the differences observed in nad9 mRNA 5' termini of two lupins differentiate L. luteus and L. angustifolius species.

Evidence that eukaryotic triosephosphate isomerase is of alpha-proteobacterial origin

We have cloned and sequenced genes for triosephosphate isomerase (TPI) from the gamma-proteobacterium Francisella tularensis, the green non-sulfur bacterium Chloroflexus aurantiacus, and the alpha-proteobacterium Rhizobium etli and used these in phylogenetic analysis with TPI sequences from other members of the Bacteria, Archaea, and Eukarya. These analyses show that eukaryotic TPI genes are most closely related to the homologue from the alpha-proteobacterium and most distantly related to archaebacterial homologues. This relationship suggests that the TPI genes present in modern eukaryotic genomes were derived from an alpha-proteobacterial genome (possibly that of the protomitochondrial endosymbiont) after the divergence of Archaea and Eukarya. Among these eukaryotic genes are some from deeply branching, amitochondrial eukaryotes (namely Giardia), which further suggests that this event took place quite early in eukaryotic evolution.

Nuclear genes associated with a single Brassica CMS restorer locus influence transcripts of three different mitochondrial gene regions

Previous studies have shown that the mitochondrial orf224/atp6 gene region is correlated with the Polima (pol) cytoplasmic male sterility (CMS) of Brassica napus. We now extend this correlation by showing that the effects of nuclear fertility restoration on orf224/atp6 transcripts cosegregate with the pol restorer gene Rfp1 in genetic crosses. We also show, however, that the recessive rfp1 allele, or a very tightly linked gene, acts as a dominant gene, designated Mmt (modifier of mitochondrial transcripts), in controlling the presence of additional smaller transcripts of the nad4 gene and a gene possibly involved in cytochrome c biogenesis. A common sequence, TTGTGG, maps immediately downstream of the 5' termini of both of the transcripts specific to plants with the Mmt gene and may serve as a recognition motif in generation of these transcripts. A similar sequence, TTGTTG, that may be recognized by the product of the alternate allele (or haplotype), Rfp1, is found within orf224 just downstream of the major 5' transcript terminus specific to fertility restored plants. Our results suggest that Rfp1/ Mmt is a novel nuclear genetic locus that affects the expression of multiple mitochondrial gene regions, with different alleles or haplotypes exerting specific effects on different mitochondrial genes.

The NADH dehydrogenase subunit 7 gene is interrupted by four group II introns in the wheat mitochondrial genome

We have characterized a wheat mitochondrial gene, designated nad7, capable of encoding a 394-amino acid subunit of the respiratory chain NADH dehydrogenase complex. It contains four introns possessing group II features and their positions differ from those in both the liverwort mitochondrial nad7 pseudogene and the nuclear gene encoding the homologous 49 kDa subunit of complex I in Neurospora. The derived amino acid sequence of the wheat nad7 gene is strongly conserved relative to its nuclear or organellar counterparts in other organisms. C-to-U type RNA editing, which is observed at 32 positions within the coding region of wheat nad7 transcripts, strengthens protein sequence similarity. RNA editing is also predicted to improve base-pairing within the domain V/VI regions of all four introns.

Higher plant mitochondria encode an homologue of the nuclear-encoded 30-kDa subunit of bovine mitochondrial complex I

We describe the structure and expression of a wheat mitochondrial gene, which codes for a subunit of mitochondrial NADH dehydrogenase. The deduced protein sequence has 70% similarity to the 30-kDa subunit of bovine mitochondrial complex I and 65% similarity to the 31-kDa subunit of Neurospora crassa complex I, components of the iron-sulfur-protein fraction, both nuclear-encoded proteins. We named this wheat mitochondrial gene as nad9. The wheat nad9 gene is transcribed in a single mRNA of 0.9 kb that is edited (C-to-U conversions) in 14 positions. Transcript mapping revealed that the first ATG codon is just 20 nucleotides downstream of the mRNA 5' end and that the 3' end is just 23 nucleotides downstream of the nad9 stop codon. The expression of the nad9 gene in plant mitochondria was studied. Polyclonal antibodies prepared against a wheat NAD9 fusion protein specifically recognise the 30-kDa subunit of bovine mitochondrial complex I and a 27.5-kDa protein in the membrane fractions of wheat, maize and common bean mitochondria, whereas the same serum recognizes a 30-kDa protein in the mitochondria of pea, chickpea and lentil.

The sugar beet mitochondrial genome contains an ORF sharing sequence homology with the gene for the 30 kDa subunit of bovine mitochondrial complex I

From a sugar beet mitochondrial DNA library, we have isolated an open reading frame (ORF192) showing extensive homology to the gene for the 30 kDa subunit of the bovine mitochondrial complex I (NADH: ubiquinone reductase). The ORF192 was found to be actively transcribed to give an RNA of approximately 1.0 kb. We have designated this gene nad9. Transcripts from the nad9 locus are edited by five C to U transitions, increasing similarity with the amino acid sequence of the corresponding bovine and Neurospora crassa polypeptides. Southern blot hybridization also indicates that nad9 is present in the mitochondrial genomes of a variety of higher plant species.