CONTROL OF PLANT-PARASITIC NEMATODES BY INTERFERENCE WITH INTERNAL TARGETS
Title: Behaviour of Heterodera glycines and Meloidogyne incognita infective juveniles exposed to nematode FMRFamide-like peptides in vitro
Submitted to: Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 6, 2011
Publication Date: June 1, 2012
Citation: Masler, E.P., Nagarkar, A., Edwards, L., Hooks, C.R. 2012. Behaviour of Heterodera glycines and Meloidogyne incognita infective juveniles exposed to nematode FMRFamide-like peptides in vitro. Nematology. 14(5):605-612.
Interpretive Summary: Plant-parasitic nematodes attack all crops of agricultural importance, causing over $10 billion in losses annually to U.S. farmers. Because several chemical pesticides used to control nematodes have been withdrawn from use, growers possess a critical need for the discovery of environmentally and economically sound nematode control agents. One approach to discovering new ways to control nematodes is to identify ways to inhibit their infectivity and reproduction using naturally derived compounds and treatments. We have previously shown that nematodes respond to amines, small molecules that are similar to those found within the nematode, by changing their behavior, which can affect hatching and infection. We have now expanded these tests to include specialized nematode peptides that control behavior and survival, and have found that two of the most important nematode pathogens of crops worldwide, the soybean cyst nematode and Southern root-knot nematode, show abnormal behaviors when exposed to selected peptides and their analogs, reducing the nematode’s ability to feed, move and infect crops. These results are significant because they show that natural agents can be used to protect host plants when they are most susceptible to nematode attack. Consequently, this information will be used by researchers in the agrochemical and agricultural biotechnology industries who are developing safe, selective methods for nematode control.
Plant-parasitic nematodes depend upon a family of neuropeptides, the FMRFamide-like peptides (FLPs), to regulate locomotion and behavior. To exploit FLPs as leads to novel nematode control agents, an understanding of how specific FLPs affect behavior, and what differences exist between species, is important. The effects of 1mM solutions of on the behaviors of Heterodera glycines and Meloidogyne incognita infective juveniles (J2) were examined in vitro. Seven FLPs, representing products of 5 flp genes and comprising a variety of amino acid sequences, were tested for their effects on J2 head movement frequency. Distinct differences in species responses were observed. KHEYLRFa and KSAYMRFa caused increased head movement frequencies in each species, but in H. glycines KHEYLRFa was 2.9-fold more potent than KSAYMRFa, while in M. incognita the potencies were equal. KHEYLRFa and KSAYMRFa were each more effective in stimulating H. glycines J2 than M. incognita J2. However, two additional FLPs, AQTFVRFa and SAPYDPNFLRFa, were stimulatory in M. incognita but not in H. glycines. KPNFIRFa, KPNFLRFa, and RNSSPLGTMRFa had no effect in either species. Substitution of d-amino acids at each position in KHEYLRFa resulted in decreased stimulation of head movement relative to the native peptide in each species, but all d-amino acid analogs were stimulatory relative to untreated controls. Substitutions in KSAYMRFa eliminated stimulatory activity in M. incognita, except for dKSAYMRFa. In H. glycines, KSdAYMRFa and KSAYMdRFa did not stimulate, KSAYdMRFa stimulated the same as the native peptide, and the remaining 4 analogs each stimulated relative to controls but below native peptide level. Analysis of the head movement behavior of large numbers of J2 of each species demonstrated that behavior is quite stable and that response to FLP treatment is highly predictable.