Insights in the evolution of plant parasitism within the phylum Nematoda based on neutral and pathogenicity-related genes.

Plant parasitism has arisen at least four times independently within the phylum Nematoda. As a starting point to reconstruct evolution of parasitism within this ubiquitous and diverse group of animals, we use (nearly full length) small subunit ribosomal DNA (SSU rDNA) sequences (˜ 1,700 bp). Currently this phylum-wide framework encompasses over 2,500 taxa, and phylogenetic analysis reveals relationships within and among these four major lineages. Remarkably, SSU rDNA - known as a conserved gene - shows accelerated evolution in case of branches dominated by taxa with short life cycles, and/or animal or plant-parasitic life styles. One of the practical implications of this characteristic is the availability of unique DNA motifs within this gene that allows for relatively straightforward high-throughput detection of plant-parasitic nematode species in complex (= environmental) samples. Currently over 30 tests have been developed including most of the high-impact root knot, cyst and lesion nematode species attacking both Solanaceous and/or cereal crops. In parallel we investigated relationships within individual lineages of plant-parasitic nematodes with regard to non-neutral, plant pathogenicity-related genes, and by doing so we tried to find clues about the role of horizontal gene transfer in the transition from bacterivores (ancestral state) towards fungivores and facultative & obligate plant parasites (most derived state). Analysis of distribution and diversity of cell wall-degrading enzymes suggest for a very early acquisition, and subsequent diversification, and it would be highly interesting to look for related patterns in effector evolution.