Recombination Events Involving the atp9 Gene Are Associated with Male Sterility of CMS PET2 in Sunflower.

Cytoplasmic male sterility (CMS) systems represent ideal mutants to study the role of mitochondria in pollen development. In sunflower, CMS PET2 also has the potential to become an alternative CMS source for commercial sunflower hybrid breeding. CMS PET2 originates from an interspecific cross of and as CMS PET1, but results in a different CMS mechanism. Southern analyses revealed differences for , and between CMS PET2, CMS PET1 and the male-fertile line HA89. A second identical copy of was present on an additional CMS PET2-specific fragment. In addition, the gene was duplicated. However, this duplication was followed by an insertion of 271 bp of unknown origin in the 5' coding region of the gene in CMS PET2, which led to the creation of two unique open reading frames and . The first 53 bp of are identical to the 5' end of . consists apart from the first 3 bp, being part of the 271-bp-insertion, of the last 228 bp of . These CMS PET2-specific orfs are co-transcribed. All 11 editing sites of the gene present in are fully edited. The anther-specific reduction of the co-transcript in fertility-restored hybrids supports the involvement in male-sterility based on CMS PET2.