Nematode parasitism genes

The ability of nematodes to live on plant hosts involves multiple parasitis m genes. The most pronounced morphological adaptations of nematodes for pla nt parasitism include a hollow, protrusible stylet (feeding spear) connecte d to three enlarged esophageal gland cells that express products that are s ecreted into plant tissues through the stylet. Reverse genetic and expresse d sequence tag (EST) approaches are being used to discover the parasitism g enes expressed in nematode esophageal gland cells. Some genes cloned from r oot-knot (Meloidogyne spp.) and cyst (Heterodera and Globodera spp.) nemato des have homologues reported in genomic analyses of Caenorhabditis elegans and animal-parasitic nematodes. To date, however, the candidate parasitism genes endogenous to the esophageal glands of plant nematodes (such as the b eta -1,4-endoglucanases) have their greatest similarity to microbial genes, prompting speculation that genes for plant parasitism by nematodes may hav e been acquired by horizontal gene transfer.