Abstract
Meloidogyne graminicola is one of the most economically important plant parasitic-nematodes (PPNs). In the present study, we determined the complete mitochondrial (mt) DNA genome sequence of this plant pathogen. Compared with other PPNs genera, this genome (19,589 bp) is only slightly smaller than that of Pratylenchus vulnus (21,656 bp). The nucleotide composition of the whole mtDNA sequence of M. graminicola is significantly biased toward A and T, with T being the most favored nucleotide and C being the least favored. The A+T content of the entire genome is 83.51%. The mt genome of M. graminicola contains 36 genes (lacking atp8) that are transcribed in the same direction. The gene arrangement of the mt genome of M. graminicola is unique. A total of 21 out of 22 tRNAs possess a DHU loop only, while tRNASer(AGN) lacks a DHU loop. The two large noncoding regions (2,031 bp and 5,063 bp) are disrupted by tRNASer(UCN). Phylogenetic analysis based on concatenated amino acid sequences of 12 protein-coding genes support the monophylies of the three orders Rhabditida, Mermithida and Trichinellida, the suborder Rhabditina and the three infraorders Spiruromorpha, Oxyuridomorpha and Ascaridomorpha, but do not support the monophylies of the two suborders Spirurina and Tylenchina, and the three infraorders Rhabditomorpha, Panagrolaimomorpha and Tylenchomorpha. The four Tylenchomorpha species including M. graminicola, P. vulnus, H. glycines and R. similis from the superfamily Tylenchoidea are placed within a well-supported monophyletic clade, but far from the other two Tylenchomorpha species B. xylophilus and B. mucronatus of Aphelenchoidea. In the clade of Tylenchoidea, M. graminicola is sister to P. vulnus, and H. glycines is sister to R. similis, which suggests root-knot nematodes has a closer relationship to Pratylenchidae nematodes than to cyst nematodes.
Highlights
Nematodes are a diverse group of bilateral animals, including free-living, insect-parasitic, animal-parasitic and plant-parasitic forms
The mt genome of M. graminicola is larger than those of four plant-parasitic nematodes (PPNs) reported to date, i.e., X. americanum (12,626 bp) [24], B. mucronatus (14,583 bp) [26], B. xylophilus (14,778 bp) [17] and R. similis (16,791 bp) [25] but slightly smaller than the mt genome of P. vulnus (21,656 bp) [17]
The larger sizes of the mt genomes of M. graminicola and P. vulnus are partly due to the presence of long noncoding regions
Summary
Nematodes are a diverse group of bilateral animals, including free-living, insect-parasitic, animal-parasitic and plant-parasitic forms. Only five entire mtDNA genome sequences derived from PPNs, including Radopholus similis, Bursaphelenchus xylophilus, Pratylenchus vulnus and B. mucronatus in the Chromadorea and Xiphinema americanum belonging to the Enoplean, have been elucidated [17,24,25,26].
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