Influence of nuclear background on transcription of a chimeric gene (orf256) and coxI in fertile and cytoplasmic male sterile wheats.

Crosses between Triticum timopheevi, as maternal donor, and T. aestivum can lead to cytoplasmic male sterile (cms) plants. The T. timopheevi derived mitochondrial DNA from parental, cms, and fertility-restored lines differs from that of T. aestivum derived mtDNA in the coxI gene region. Our previous results for cms lines showed that there is an open reading frame, orf256, upstream from coxI in T. timopheevi derived mtDNA that is not present in T. aestivum DNA. The 5' flanking region and the first 33 nucleotides of the coding region of orf256 are identical to the corresponding region of T. aestivum coxI, whereas the rest of orf256, including the 3' flank, is not related to coxI. Also, the organization of orf256 and coxI on a HindIII fragment from T. timopheevi derived mtDNA are identical in T. timopheevi, cms, and fertility-restored lines. We now report that the DNA sequence of orf256 is identical in T. timopheevi, cms, and fertility-restored lines. Major transcripts in cms and fertility-restored lines encode both orf256 and coxI with 5' termini like coxI mRNA of T. aestivum, whereas parental mitochondria from T. timopheevi have major transcripts with 5' termini within the orf256 coding region. Mitochondria from cms and fertility-restored lines have the potential to produce a protein that would not be present in parental T. timopheevi or in T. aestivum.