Complete mitochondrial genome of Mentha spicata L. reveals multiple chromosomal configurations and RNA editing events.

Mentha spicata L. is a valuable plant that yields spearmint oil, widely utilized in the pharmaceutical, chemical, and cosmetic industries. The mitochondrial genome (mitogenome) is an essential material for molecular breeding and evolution studies. Here, the mitogenome of M. spicata was assembled by combining Nanopore and Illumina reads. It consisted of a linear chromosome (Ch1) and two circular chromosomes (Ch2 and Ch3). Furthermore, we showed two pairs of repeats (R1 and R2) mediated recombinations resulting in multiple chromosomal configurations. The R1-mediated-recombination generated a large molecule formed by joining Ch2 and Ch1. Similarly, the R2-mediated-recombination generated a large molecule formed by joining Ch3 and Ch1. Then, we identified 17 mitochondrial plastid DNAs (MTPTs) by comparing the mitogenome and cpgenome. The MTPT14 was conserved in multiple species, which has undergone the same evolutionary process as the two organellar genomes among M. spicata, Hesperelaea palmeri and Castilleja paramensis. Based on the RNA-seq reads, 246 RNA editing sites were predicted, resulting in the conversion of cytosine to uracil bases. Furthermore, we successfully validated 40 out of 43 predicted sites. This project reported a complex structure of the M. spicata mitogenome resulting from repeat-mediated recombinations, which will provide valuable information for gene function study and the breeding of different varieties.