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Phytopathology,
2001]
Bacillus thuringiensis (Bt) delta-endotoxins, a family of crystal (Cry) proteins, are widely used as insecticides in agriculture. Recently, we described that Bt toxins may be also effective nematicides. To more fully address the potential of Cry toxins as nematicides to control plant-parasitic-nematodes: (PPNs), we analyzed the toxicities of eight Cry proteins (Cry 5A, 5B, 6A, 6B, 12A, 13A, 14A, and 21A) on five free-living nematodes (C. elegans, Pristionchus pacificus, Panagrellus redivivus, Acrobeloides, and Distolabrellus veechi). The results of general toxicity assays, morphology, and brood size indicated that indeed some of these Cry proteins are potent nematicidal toxins. However, some had little effect on nematodes. One nematode species was resistant to all toxins. We found that one Bt toxin could be trimmed to a small 42 kD active core that was toxic to almost all these diverse nematodes. We believe that Bt toxins show good potential to control PPNs.
[
International C. elegans Meeting,
2001]
Bacillus thuringiensis (Bt) delta-endotoxins, a family of crystal (Cry) proteins, are widely used as insecticides in agriculture. Recently, we described two Bt toxins (Cry5B and Cry6A) that are effective at killing C. elegans . Here, we test whether Bt toxins are generally nematicidal. We analyzed the toxicities of eight Cry proteins (Cry 5A, 5B, 6A, 6B, 12A, 13A, 14A, and 21A) on five free-living nematodes species ( C. elegans, Pristionchus pacificus, Panagrellus redivivus, Acrobeloides sp. , and Distolabrellus veechi ). The results of health assays, morphology, and brood size indicated that four out of the eight proteins were nematicidal and were able to kill multiple nematodes species. One nematode species was resistant to all toxins. Bt toxin was toxic to all four of the other free-living nematodes tested, including one species closely related to plant-parasitic nematodes (PPNs). Structure function studies indicate it can be trimmed to a small 42 kD active core that retains full toxicity. Given its effects on many free-living nematodes and that PPNs are able to exclude large proteins from their diet, this small toxin holds promise for controlling plant-parasitic nematodes. To test this directly, we are transforming Arabidopsis plants and tomato hairy roots with the Bt toxin under control of three different promoters. Currently, successfully transformed plant lines are being isolated and our nematode infection assays are being perfected. We are growing Arabidopsis plants in modified Knop medium and are infecting them with active Meloidogyne incognita J2's under sterile conditions. We hope to soon assay whether expression of the toxin adversely affects infection rates and survival of M. incognita .