The physical map and organisation of the mitochondrial genome from the fertile cytoplasm of maize

DNA synthesis in purified maize mitochondria

We have developed an in organelle DNA synthesis system using isolated mitochondria from maize. The organelles used in this assay are shown to be intact by a number of criteria. Both the high molecular weight components and the smaller plasmid-like components of the mitochondrial genome are used as templates; however, the plasmid-like elements are relatively more active as templates. The termini of the linear plasmids--S-1, S-2 and the 2.3 kbp plasmids--are more highly labelled than internal regions, probably as a result of filling in of gaps at the termini mediated by a DNA polymerase or to exonuclease degradation of the 3' OH termini, with subsequent filling in. Although most of the DNA synthesis observed in this system most likely results from this type of synthesis at DNA nicks or termini, a small amount of specific, potentially replication-associated, synthesis is also detected.

Cytoplasmic reversion to fertility in cms-S maize need not involve loss of linear mitochondrial plasmids

Cytoplasmic male sterility of the S type (cms-S) in maize is characterized by the presence of two autonomously replicating plasmid-like elements, S1 and S2. These plasmids have not been found in the mitochondrial genomes of normal (male-fertile) maize nor previously in male-fertile cytoplasmic revertants. This paper reports the discovery of spontaneous cytoplasmic reversion to fertility in cms-S maize not involving the loss of S1 and S2 plasmids. Data are presented showing that loss of the plasmids during cytoplasmic reversion is under nuclear influence and is not a characteristic of the S cytoplasm itself.

The maize cytochrome c oxidase subunit I gene: sequence, expression and rearrangement in cytoplasmic male sterile plants

The single copy of the gene for cytochrome c oxidase subunit I (COX I) present in the mitochondrial genome of fertile maize (Zea mays L.) is encoded by a continuous open reading frame of 1584 nucleotides. The predicted polypeptide encoded by the gene has a mol. wt. of 58 219 daltons and shows >60% amino acid sequence homology with the corresponding fungal and animal polypeptides. Two major transcripts of 2400 and 2300 nucleotides can be detected and the 5' end of the larger transcript maps to a sequence from -161 to -153 (relative to the initiator codon) which shows high homology to the yeast mitochondrial promoter. In mitochondrial DNA from the S male-sterile cytoplasm of maize, which also characteristically contain two low mol. wt. linear DNAs (S1 and S2), rearrangements just 5' (at -175) to the COX I gene, generate additional DNA restriction fragments containing entire copies of the gene. These rearrangements involve a sequence identical to the terminal 186 bp of the 208-bp inverted repeat sequence found at either end of the S1 and S2 DNAs.

The mitochondrial genome of fertile maize (Zea mays L.) contains two copies of the gene encoding the alpha-subunit of the F1-ATPase

In contrast to the situation in animals and fungi the alpha-subunit of the mitochondrial F1-ATPase is encoded by two identical mitochondrial genes (ATP A) in male fertile maize (Zea mays L.). Cytoplasmic male sterile (T, C and S) maize mitochondrial genomes only contain a single copy of the gene. Sequence analysis reveals that the uninterrupted coding region of both copies of the gene is 1,524 bp long and encodes a polypeptide of 508 amino acids with a molecular weight of 55,117. The predicted amino acid sequence shares over 60% homology with the nuclear encoded alpha-subunit from yeast and bovine ATPase and approx. 50% with the corresponding chloroplast and bacterial polypeptides.

The endpoints of an inversion in wheat chloroplast DNA are associated with short repeated sequences containing homology to att-lambda

The endpoints of an inversion in wheat chloroplast DNA are shown to be associated with copies of a short repeated sequence. Recombination across the repeats in an inverted configuration may have been responsible for the inversion, although they are currently in a direct orientation owing to a second inversion. The repeated sequence contains an element homologous to the core of the bacteriophage lambda att-site, which can function as such in vivo.