A mitochondrial 16 kDa protein is associated with cytoplasmic male sterility in sunflower

Cytoplasmic male-sterile lines CMS89 and CMSBaso of sunflower (Helianthus annuus) differ from the fertile lines HA89 and Baso in a mitochondrial DNA sequence in the vicinity of the atpA gene. In addition, the transcriptional pattern of the atpA gene is changed in male-sterile lines compared to fertile ones. Besides one main transcript in the fertile lines, the male-sterile lines additionally show larger transcripts. Investigation of Baso and CMSBaso revealed that the two fertility-restored lines of CMS89 have the same transcripts as CMSBaso or a combination of CMSBaso and CMS89. Comparing the mitochondrial in organello translation products we observed a unique 16 kDa protein, which is expressed in male-sterile lines carrying the H. petiolaris cytoplasm but is not detectable in fertile lines with H. annuus cytoplasm. The 16 kDa protein can also be observed in restored lines but not in H. petiolaris. As the expression of the 16 kDa polypeptide seems to be linked to the interspecific cross between H. petiolaris and H. annuus it may play a role in CMS. By different criteria such as molecular mass, isoelectric point and peptide fingerprinting the alpha subunit of the F1-ATPase of male-sterile and fertile lines is very similar if not identical.