TABLE CONTENTS

The Meloidogyne incognita Genome Sheds Light on Plant Parasitism in
Metazoan
Abad, P. & International Sequencing and Annotation Consortium
UMR INRA 1301-UNSA-CNRS 6243 - Interactions Biotiques et Santé Végétale, Sophia Antipolis, France
Despite the plethora of information available for the free living nematode Caenorhabditis
elegans and its sister species C. briggsae, very little is known about the other members of this
diverse phylum. This is particularly notable for parasitic nematodes, which constitute half of
the earth’s nematodes, and which have remained largely unexplored. Recently, the genome
sequence of the human filarial nematode parasite Brugia malayi has revealed significant
differences with Caenorhabditis spp., and underlined the need to obtain additional genome
data from representative species to investigate the outstanding diversity of the phylum[1].
The Southern root-knot nematode Meloidogyne incognita is a mitotic parthenogenetic
parasite able to infect the roots of almost all cultivated plants, which possibly renders this
species the most damaging crop pathogen in the world [2]. Here, I will present data obtained
by a consortium of laboratories involved in the annotation of the genome sequence of this
nematode. The main points of our studies are as follows:
- The spectacular presence of an extensive set of plant cell wall-degrading enzymes in this
nematode, which has no equivalent in any animal studied to date. This suite of enzymes is
likely to modify and subvert the host environment to support nematode growth. As M.
incognita can infect the model plant Arabidopsis thaliana, our data make it a key model
system for the understanding of adaptations to phytoparasitism by metazoans.
- The striking similarity of some pathogenicity genes to bacterial homologues, suggesting
that these genes were acquired by multiple horizontal gene transfer (HGT) events. While
inter-species HGT has been a major component of evolution in prokaryotes and some
protozoa, HGT into metazoan genomes is relatively rare.
- Most of the genome is present in pairs of homologous but divergent segments,
suggesting that this species is evolving in the absence of sex towards effective haploidy.
These observations are consistent with a strictly mitotic parthenogenetic reproductive mode
which can permit homologous chromosomes to diverge considerably, as hypothesised for
bdelloid rotifers[3-4] Such genetic plasticity could explain the explain the extremely wide
host range and geographic distribution of this polyphagous nematode.
- Finally, the comparative analysis with the free-living nematode C. elegans and the
human parasite B. malayi reveals profound genomic diversity within this phylum, helping to
account for the unmatched evolutionary success of these metazoans.
1. Ghedin, E., et al., Draft genome of the filarial nematode parasite Brugia malayi. Science, 2007. 317(5845): p. 1756-60.
2. Trudgill, D.L. and V.C. Blok, Apomictic, polyphagous root-knot nematodes: exceptionally successful and damaging
biotrophic root pathogens. Annu Rev Phytopathol, 2001. 39: p. 53-77.
3. Mark Welch, D. and M. Meselson, Evidence for the evolution of bdelloid rotifers without sexual reproduction or genetic
exchange. Science, 2000. 288(5469): p. 1211-5.
4. Pouchkina-Stantcheva, N.N., et al., Functional divergence of former alleles in an ancient asexual invertebrate. Science,
2007. 318(5848): p. 268-71.
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