Comparisons of mitochondrial genomes of CMS line and its nuclear and cytoplasmic donors uncover the genome rearrangement and CMS associated candidate gene in eggplant.

Male sterile lines of eggplant (Solanum melongena L.) have been developed using the cytoplasm of S. aethiopicum Group Aculeatum (Saet), but the underlying mechanism remains unknown. In this study, cytoplasmic male sterility (CMS) line EP28A, its nuclear donor EP28 and cytoplasmic donor Saet were used for comparative analysis. Cytological analysis showed that male sterility in EP28A is due to abnormal tapetum development, which prevents the formation of pollen mother cells. To further investigate the molecular basis, three mitochondrial genomes were sequenced and assembled. Comparative analyses indicated that EP28A mitochondrial genome was largely derived from Saet, yet exhibited variations in genome size, genome structure, and the gene copy numbers. Sequence alignment demonstrated a high conservation of protein coding genes between EP28A and Saet. Further analysis identified orf218b as a CMS associated candidate gene. Above results revealed mitochondrial genome variation caused by interspecific hybridization, and provided insight into the application of CMS in eggplant breeding.