Cytoplasmic Male Sterility Based on the PET2 Cytoplasm in Sunflower

Cytoplasmic male sterility (CMS) is a trait in higher plants in which these fail to produce or shed functional pollen. Rearrangements in the mitochondrial DNA have been shown to be the cause for cytoplasmic male sterility in a number of plant species. Understanding the mechanism behind male sterility allows the study of the role of mitochondria in pollen development. This is important as CMS is widely used in hybrid breeding to ensure cross pollination. Commercial sunflower hybrid breeding is so far entirely based on the use of the PET1 cytoplasm. This represents a high risk for pathogen specialization due to the narrow genetic base on the cytoplasmic side. A new CMS source in sunflower, the so called PET2 cytoplasm, would represent an interesting alternative. Although CMS PET1 and CMS PET2 have been derived from the same interspecific cross of H. petiolaris with H. annuus the CMS mechanism behind the two CMS sources is totally different. In CMS PET2, a duplication of the atp9 gene followed by an insertion results in two new open reading frames orf288 and orf231 associated with male sterility. The two orfs are co-transcribed and the co-transcript is anther-specific reduced in the fertility-restored hybrids.