Abstract
Root-knot nematodes (RKNs) are parasitic animals that invade root systems of many agricultural plants. RKNs are effective parasites because they induce permanent feeding sites inside plant roots as juveniles, and then spend their whole life-cycle at this single site. During initial infection, RKNs interact with root tips and move between cells to reach a final target destination near developing vascular cells. It is thought that successful infection by RKNs involves a suppression of defense responses. We have investigated this hypothesis by quantitative measurement of host defense response during invasion of tomato roots by the northern root-knot nematode, Meloidogyne hapla. Control experiments revealed that the defense response differs in roots from that typically observed in aerial tissues. During RKN invasion, a significant induction of the "root defense marker genes" was observed, demonstrating that a susceptible host does indeed recognise early RKN parasitism. These results indicate that suppression of host defense is not required for RKNs to establish an infection site, and that these signalling networks may even by used to guide the infection process.
