紫花苜蓿线粒体基因组结构与特征分析OA

Alfalfa(Medicago sativa L.)is an important leguminous forage grass,and characterization of its mitochondrial genome(mtDNA)is essential for understanding its evolutionary biology and supporting genetic improvement.In this study,the complete mtDNA sequence of the strain'Qingda No.1'was assembled and analyzed.The mtDNA is 290 285 bp in length and contains 35 protein-coding genes,15 transfer RNA(tRNA)genes,and three ribosomal RNA(rRNA)genes.A total of 56 simple sequence repeats(SSRs)and 48 long repeat sequences were identified.Analysis of synonymous and nonsynonymous substitution rates showed that most protein-coding genes were under purifying selection,with Ka/Ks ratio below 1,whereas rps1 and nad9 exhibited Ka/Ks ratio greater than 1,suggesting possible positive selec-tion.Inverted repeat(IR)boundary analysis indicated that the alfalfa mtDNA was more compact compared with other legumes such as soybean(Glycine max),and tetranucleotide repeats represented the predomi-nant SSR type.Phylogenetic analysis confirmed a close evolutionary relationship between M.sativa and Medicago truncatula.Codon usage bias analysis revealed a preference for codons ending with A or U,and neutrality and ENC-plot analyses indicated that natural selection played a major role in shaping codon usage bias.