Cistanche Species Mitogenomes Suggest Diversity and Complexity in Lamiales-Order Mitogenomes

The extreme diversity and complexity of angiosperms is well known. Despite the fact that parasitic plants are angiosperms, little is known about parasitic plant mitogenomic diversity, complexity, and evolution. In this study, we obtained and characterized the mitogenomes of three Cistanche species (holoparasitic plants) from China to compare the repeats, segment duplication and multi-copy protein-coding genes (PCGs), to clarify the phylogenetic and evolution relationship within the Lamiales order, and to identify the mitochondrial plastid insertions (MTPT) in Cistanche mitogenomes. The results showed that the mitogenome sizes of the three Cistanche species ranged from 1,708,661 to 3,978,341 bp. The Cistanche species genome encodes 75-126 genes, including 37-65 PCGs, 31-58 tRNA genes and 3-5 rRNA genes. Compared with other Lamiales and parasitic species, the Cistanche species showed extremely high rates of multi-copy PCGs, ranging from 0.13 to 0.58 percent of the total number of PCGs. In addition, 37-133 Simple Sequence Repeat (SSRs) were found in these three mitogenomes, the majority of which were the mononucleotides Adenine/Thymine. The interspersed repeats contained forward and palindromic repeats. Furthermore, the segment-duplication sequence size ranged from 199,584 to 2,142,551 bp, accounting for 24.9%, 11.7% and 53.9% of the Cistanche deserticola, Cistanche salsa and Cistanche tubulosa mitogenome, respectively. Furthermore, the Ka/Ks analysis suggested that the atp4, ccmB, ccmFc and matR were probably positively selected during Lamiales evolution. The Cistanche plastome suggested the presence of MTPT. Moreover, 6-12 tRNA, 9-15 PCGs fragments and 3 rRNA gene fragments in the Cistanche mitogenomes were found in the MTPT regions. This work reports the Cistanche species mitogenome for the first time, which will be invaluable for study the mitogenome evolution of Orobanchaceae family.