Diversity of mitochondrial plastid DNAs (MTPTs) in seed plants

Mitochondrial plastid DNAs (MTPTs) refer to plastid-derived DNA fragments in mitochondrial genomes. While the MTPTs have been described for numerous species, its overall patterns have not been examined in details. Here, we carried out a systematic analysis of MTPTs among 73 plant species, including 28 algae, 1 liverwort, 2 moss, 1 lycophyte, 1 gymnosperm, 1 magnoliid, 12 monocots, 26 eudicots and 1 relic angiosperm Amborella trichopoda. A total of 300 MTPT gene clusters were found in 39 seed plants, which represented 144 MTPT gene cluster types. The detected MTPT gene clusters were evaluated in seven aspects, and they were found to be enriched particularly in monocots and asterids of eudicots. Some MTPT gene clusters were found to be shared by closely related species. All chloroplast genes were found in MTPTs, suggesting that there is no functional relevancy for genes that were transferred. However, after calculation of the frequency of the 115 chloroplast genes, five hot spots and three cold spots were discovered in chloroplast genome. In summary, this study demonstrated the high degree of diversity in MTPTs. The discovered MTPTs would facilitate the accurate assembly of chloroplast and mitochondrial genomes as well as the understanding of organelle genome evolution.