Mitogenome of Medicago lupulina L. Cultivar-Population VIK32, Line MlS-1: Dynamic Structural Organization and Foreign Sequences

This study presents the complete assembly and analysis of the mitochondrial genome (mitogenome) of Medicago lupulina L. var. vulgaris Koch, cultivar-population VIK32, line MlS-1, which forms an effective symbiosis not only with arbuscular mycorrhiza but also with the root nodule bacteria Sinorhizobium meliloti. The assembly, generated using a hybrid sequencing approach, revealed sequences of putative horizontal origin. These include a highly conserved open reading frame (ORF), orf279, encoding a protein structurally homologous to maturase K, yet bearing remote similarity to bacterial reverse transcriptases and CRISPR-associated proteins. We also identified sequences homologous to mitovirus RNA-dependent RNA polymerases and a fragment of the chloroplast 23S ribosomal RNA (rRNA), suggesting historical gene transfers from viruses and plastids. This work establishes a foundation for investigating the role of mitochondrial genome variation in key plant’s phenotypic traits, such as the enhanced responsiveness to arbuscular mycorrhiza observed in this agronomically valuable line.