Assembly and comparative analysis of the complete mitochondrial genome of Trigonella foenum-graecum L.

Background: Trigonella foenum-graecum L. is a Leguminosae plant, and the stems, leaves, and seeds of this plant are rich in chemical components that are of high research value. The chloroplast (cp) genome of T. foenum-graecum has been reported, but the mitochondrial (mt) genome remains unexplored.

Results: In this study, we used second- and third-generation sequencing methods, which have the dual advantage of combining high accuracy and longer read length. The results showed that the mt genome of T. foenum-graecum was 345,604 bp in length and 45.28% in GC content. There were 59 genes, including: 33 protein-coding genes (PCGs), 21 tRNA genes, 4 rRNA genes and 1 pseudo gene. Among them, 11 genes contained introns. The mt genome codons of T. foenum-graecum had a significant A/T preference. A total of 202 dispersed repetitive sequences, 96 simple repetitive sequences (SSRs) and 19 tandem repetitive sequences were detected. Nucleotide diversity (Pi) analysis counted the variation in each gene, with atp6 being the most notable. Both synteny and phylogenetic analyses showed close genetic relationship among Trifolium pratense, Trifolium meduseum, Trifolium grandiflorum, Trifolium aureum, Medicago truncatula and T. foenum-graecum. Notably, in the phylogenetic tree, Medicago truncatula demonstrated the highest level of genetic relatedness to T. foenum-graecum, with a strong support value of 100%. The interspecies non-synonymous substitutions (Ka)/synonymous substitutions (Ks) results showed that 23 PCGs had Ka/Ks < 1, indicating that these genes would continue to evolve under purifying selection pressure. In addition, setting the similarity at 70%, 23 homologous sequences were found in the mt genome of T. foenum-graecum.

Conclusions: This study explores the mt genome sequence information of T. foenum-graecum and complements our knowledge of the phylogenetic diversity of Leguminosae plants.