A transcriptional alteration on the atp9 gene is associated with a sunflower male-sterile cytoplasm

The transcriptional patterns of six mitochondrial genes were studied in dif ferent nuclear backgrounds for four sunflower cytoplasmic male sterility (C MS) lines. Probes coding for cob, coxI, coxII and atp6 did not detect diffe rences between the CMS lines and male-fertile lines. atpA transcripts seeme d to be dependent on the cytotype but were not related to the CMS trait in the genotypes studied. However, the atp9 probe detected transcripts of 500 and 1,100 nt in the CMS-PEF1, while the fertile forms showed a single trans cript of 650 nt. Nuclear genes that restore fertility specifically rectifie d this alteration, suggesting that modified atp9 transcripts are associated with CMS in PEF1 sunflower. Cloning and sequencing of atp9 from CMS-PEF1 a nd comparison with the corresponding male-fertile gene showed the insertion of a 0.5-kbp sequence in the 3' UTR of the gene that may be at the origin of the PEF1-CMS and the altered transcripts detected in this study.