Molecular Biology and Evolution, Vol 14, 40-48, Copyright © 1997 by Society for Molecular Biology and Evolution
A Hugall, J Stanton and C Moritz
Mitochondrial DNA of the root knot nematode Meloidogyne hapla was
investigated for intraspecific diversity and divergence from other
parthenogenetic root knot nematodes. A 1,900-bp fragment containing COII,
tRNAHis, 16S rRNA, ND3 and Cyt b genes has been cloned and sequenced from
one individual and an 1,188-bp region within this region was sequenced from
four other Australian isolates. M. hapla mtDNA is more than 80% AT-rich,
like other Meloidogyne spp. Nucleotide diversity within M. hapla is some
10-fold higher than across three other parthenogenetic species of root-knot
nematode (M. arenaria, M. javanica, and M. incognita), implying an earlier
origin for M. hapla. Nucleotide divergence between M. hapla and its
congener M. javanica is as great as that between Ascaris suum and
Caenorhabditis elegans, members of different nematode subclasses, while
amino acid sequence difference between Meloidogyne is more than twice as
great. This is interpreted as an AT-bias-induced acceleration of the amino
acid substitution rate, over and above saturation of nucleotide divergence
in the strongly AT-biased DNA, on three lines of evidence: (1) in conserved
blocks in 16S rDNA congeneric Meloidogyne have no more differences than
between A. suum and C. elegans; (2) the Meloidogyne lineage has more amino
acid changes relative to the Ascaris/Caenorhabditis lineage with respect to
four of five outgroups, the exceptional outgroup being the only species
(Apis) as AT-rich as Meloidogyne; and (3) between the two Meloidogyne there
are more first and second but fewer third codon position changes than
between the other nematode species. M. hapla is also found to contain a
102-bp tandem repeat of at least 40 copies; a size, arrangement, and
position the same as in M. javanica, but sequence comparisons did not
demonstrate homology between the two repeats.
ORIGINAL ARTICLE
Evolution of the AT-rich mitochondrial DNA of the root knot nematode, Meloidogyne hapla
Co-operative Research Centre for Tropical Plant Pathology, University of Queensland, Australia. a.hugall@mailbox.uq.oz.au
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