Genetic diversity within the mitochondrial genome of Bursaphelenchus xylophilus

Abstract

Pine wilt disease, a major threat to conifer forests worldwide, is caused by the pinewood nematode, Bursaphelenchus xylophilus. Although native to North America, B. xylophilus was introduced in Japan, China, Taiwan, Korea and, more recently, in Portugal through timber trade. Morphological plasticity and overlap of phenotype within the genus Bursaphelenchus makes species classification difficult and therefore inter- and intra-specific genetic surveys are mandatory. In this context, the variability of mitochondrial DNA (mtDNA) sequences has been successfully used as a tool for species identification and to study evolutionary relationships among many eukaryotic lineages. Here we report the partial sequence of the B. xylophilus mitochondrial genome. A comparative analysis using the complete mitochondrial genome of 32 nematode species shows that B. xylophilus mtDNA has a unique gene order in the phylum Nematoda that resulted from, at least, two major rearrangement events involving the AT-rich region and the Asparagine tRNA gene. We also confirm that B. xylophilus and B. mucronatus are distinct phylogenetic groups, that B. xylophilus retains higher genetic diversity in its geographical origin, in North America, and that it was recently introduced in the Iberian Peninsula by a unique long-distance dispersal of a small pioneer population from Asia. The catalogue of new B. xylophilus mtDNA sequences provides the necessary information to carry out taxonomic, ecological and population studies.