Cytoplasmic male sterility in sunflower is correlated with the co-transcription of a new open reading frame with the atpA gene.
The organization and expression of the mitochondrial (mt) genome of fertile, male-sterile and restored lines of Helianthus annuus and of H. petiolaris were compared to identify alterations which might lead to cytoplasmic male sterility (CMS). The mtDNAs of fertile and male-sterile lines differ by an 11 kb inversion and a 5 kb insertion. The rearrangements seem to be the result of recombination events within an inverted repeat of 261 bp. Detectable alterations in the transcript pattern of the rearranged mtDNA regions are restricted to the atpA locus. The male-sterile line CMSBaso shows three additional transcripts of the atpA locus of about 2500, 1200 and 250 nucleotides which are not detectable in Baso. However, the coding sequences of the atpA gene are entirely identical in the fertile line Baso and the male-sterile line CMSBaso. But a new open reading frame (orfH522) of 522 nucleotides is co-transcribed with the atpA gene as an additional larger transcript of about 2500 nucleotides in CMSBaso. orfH522 is also included in a second additional transcript of about 1200 nucleotides. The predicted translation product of orfH522 might play a role in CMS in sunflower.