MITOCHONDRIAL-DNA OF CYTOPLASMIC MALE-STERILE TRITICUM-TIMOPHEEVI - REARRANGEMENT OF UPSTREAM SEQUENCES OF THE ATP6 AND ORF25 GENES

The organization of mitochondrial DNA (mtDNA) and transcript patterns of the atp6 and orf25 genes were examined in cytoplasmic male-sterile (CMS) and fertile Triticum lines. Major differences are observed betwe en CMS T. timopheevi and fertile T. aestivum for both mitochondrial ge nes. The T. aestivum mt genome carries two atp6 gene copies, whereas o nly a single copy of the atp6 gene is present in T. timopheevi mtDNA. Sequence data suggest that identical sequences upstream of the atp6 ge ne and the orf25 gene are involved in homologous recombination in both cytoplasms. The differences in the upstream sequences of the atp6 or the orf25 genes affect transcript sizes in both cytoplasms. Transcript ion initiation may occur at conserved promoter elements located at var iable distances upstream of the aminoacid coding sequences. The correl ation between the gene rearrangements and the CMS phenomenon in T. tim opheevi is discussed.