Update on Nematodes: Sophisticated Parasites of Legumes Nematodes. Sophisticated Parasites of Legumes

From an agronomic perspective, the interactions of phytoparasitic nematodes with leguminous crops can be devastating (Barker, 1998). On a cellular and molecular level, the complexities of the interactions of these microscopic worms with legumes are comparable to those of well-known symbionts (Mathesius, 2003). Because of their agricultural importance, the soybean cyst nematode Heterodera glycines and species of root-knot nematodes (Meloidogyne spp.) that infect soybean (Glycine max) and other legumes have emerged as primary research models to understand the signaling, perception, and response events during plant-nematode interactions (Davis et al., 2004). The recent advances in our understanding of the cellular, physiological, and molecular basis of legumenematode interactions are merging at the crossroads of plant-microbe interactions and plant developmental biology. All plant-parasitic nematodes have evolved a hollow, protrusible mouth spear called a stylet that is used to inject secretions into host tissues and pierce plant cell walls to withdraw nutrients (Hussey and Grundler, 1998). Some phytonematode species feed upon and quickly destroy plant cells as migratory parasites, whereas other nematode species become sedentary in later life stages and must modify plant cells to provide a sustained local source of nutrition for parasitic success. Although species within a few nematode genera, such as Ditylenchus and Aphelenchoides, plague the shoot tissues of cultivated legumes such as alfalfa (Medicago sativa), the majority of phytonematode species are parasites of plant roots (Hussey and Grundler, 1998). The root-knot nematodes and cyst nematodes (Heterodera and Globodera spp.) are sedentary endoparasites of plant roots and the primary nematode pathogens of most crop species worldwide, including many cultivated legumes (Barker, 1998). The major species of Meloidogyne have a wide host range that includes at least 1,700 plant species (Barker, 1998). By contrast, individual species of cyst nematodes are relatively host specific, such as the soybean cyst nematode H. glycines that infects relatively few plant species beyond soybean (Hussey and Grundler, 1998). As members of the same family (Heteroderidae), however, both root-knot and cyst nematodes share similar parasitic habits, most notably the induction of elaborate modifications of selected plant root cells into complex feeding sites (Fig. 1).