Organization Features of the Mitochondrial Genome of Sunflower (Helianthus annuus L.) with ANN2-Type Male-Sterile Cytoplasm

This study provides insights into the flexibility of the mitochondrial genome in sunflower (Helianthus annuus L.) as well as into the causes of ANN2-type cytoplasmic male sterility (CMS). De novo assembly of the mitochondrial genome of male-sterile HA89(ANN2) sunflower line was performed using high-throughput sequencing technologies. Analysis of CMS ANN2 mitochondrial DNA sequence revealed the following reorganization events: twelve rearrangements, seven insertions, and nine deletions. Comparisons of coding sequences from the male-sterile line with the male-fertile line identified a deletion of orf777 and seven new transcriptionally active open reading frames (ORFs): orf324, orf327, orf345, orf558, orf891, orf933, orf1197. Three of these ORFs represent chimeric genes involving atp6 (orf1197), cox2 (orf558), and nad6 (orf891). In addition, orf558, orf891, orf1197, as well as orf933, encode proteins containing membrane domain(s), making them the most likely candidate genes for CMS development in ANN2. Although the investigated CMS phenotype may be caused by simultaneous action of several candidate genes, we assume that orf1197 plays a major role in developing male sterility in ANN2. Comparative analysis of mitogenome organization in sunflower lines representing different CMS sources also allowed identification of reorganization hot spots in the mitochondrial genome of sunflower.