Ecotypes of the model legume Lotus japonicus vary in their interaction phenotypes with the root-knot nematode Meloidogyne incognita.

BACKGROUND AND AIMS: Knowledge of host factors affecting plant-nematode interactions is scarce. Here, relevant interaction phenotypes between a nodulating model host, Lotus japonicus, and the endoparasitic root-knot nematode Meloidogyne incognita are assessed via a genetic screen. METHODS: Within an alpha experimental design, 4-week-old replicate plants from 60 L. japonicus ecotypes were inoculated with 1000 nematodes from a single egg mass population, and evaluated for galling and nematode egg masses 6 weeks after inoculation. KEY RESULTS: Statistical analysis of data for 57 ecotypes showed that ecotype susceptibilities ranged from 3.5 to 406 galls per root, and correlated strongly (r = 0.8, P < 0.001, log scale) with nematode reproduction (ranging from 0.6 to 34.5 egg masses per root). Some ecotypes, however, showed a significant discrepancy between disease severity and nematode reproduction. Necrosis and developmental malformations were observed in other infected ecotypes. CONCLUSIONS: The first evidence is provided of significant variability in the interactions between L. japonicus and root-knot nematodes that may have further implications for the genetic dissection and characterization of host pathways involved in nematode parasitism and, possibly, in microbial symbiosis.

Functionality of resistance gene Hero, which controls plant root-infecting potato cyst nematodes, in leaves of tomato.

The expression of host genomes is modified locally by root endoparasitic nematode secretions to induce the development of complex cellular structures referred as feeding sites. In compatible interactions, the feeding sites provide the environment and nutrients for the completion of the nematode's life cycle, whereas in an incompatible (resistant) interaction, the host immune system triggers a plant cell death programme, often in the form of a hypersensitive reaction, which restricts nematode reproduction. These processes have been studied in great detail in organ tissues normally infected by these nematodes: the roots. Here we show that host leaves can support a similar set of programmed developmental events in the potato cyst nematode Globodera rostochiensis life cycle that are typical of the root-invading nematodes. We also show that a gene-for-gene type specific disease resistance that is effective against potato cyst nematodes (PCN) in roots also operates in leaves: the expression of the resistance (R) gene Hero and members of its gene family in leaves correlates with the elicitation of a hypersensitive response only during the incompatible interaction. These findings, and the ability to isolate RNA from relevant parasitic stages of the nematode, may have significant implications for the identification of nematode factors involved in incompatible interactions.