Genetic Basis of Cry1F-Resistance in a Laboratory Selected Asian Corn Borer Strain and Its Cross-Resistance to Other Bacillus thuringiensis Toxins

Transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) have revolutionized pest control, but the benefits of this approach have been reduced by the evolution of resistance in pests. The widely adopted ’pyramid strategy’ for delaying resistance entails transgenic crops producing two or more distinct toxins that kill the same pest. The limited experimental evidence supporting this strategy comes primarily from a model system under ideal conditions. Here we tested the pyramid strategy under nearly worst-case conditions, including some cross-resistance between the toxins in the pyramid. In a laboratory selection experiment with an artificial diet, we used Bt toxins Cry1Ab, Cry1F, and Cry1Ie singly or in pairs against Ostrinia furnacalis, one of the most destructive pests of corn in Asia. Under the conditions evaluated, pairs of toxins did not consistently delay the evolution of resistance relative to single toxins.

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Characterization of Chimeric Bacillus thuringiensis Vip3 Toxins

Applied and Environmental Microbiology ◽

10.1128/aem.02079-06 ◽

2006 ◽

Vol 73 (3) ◽

pp. 956-961 ◽

Cited By ~ 82

Author(s):

Jun Fang ◽

Xiaoli Xu ◽

Ping Wang ◽

Jian-Zhou Zhao ◽

Anthony M. Shelton ◽

...

Keyword(s):

Bacillus Thuringiensis ◽

Trichoplusia Ni ◽

European Corn Borer ◽

Insect Pest ◽

Chimeric Protein ◽

Fall Armyworm ◽

Terminal Region ◽

Cabbage Looper ◽

Cross Resistance ◽

Corn Borer

ABSTRACT Bacillus thuringiensis vegetative insecticidal proteins (Vip) are potential alternatives for B. thuringiensis endotoxins that are currently utilized in commercial transgenic insect-resistant crops. Screening a large number of B. thuringiensis isolates resulted in the cloning of vip3Ac1. Vip3Ac1 showed high insecticidal activity against the fall armyworm Spodoptera frugiperda and the cotton bollworm Helicoverpa zea but very low activity against the silkworm Bombyx mori. The host specificity of this Vip3 toxin was altered by sequence swapping with a previously identified toxin, Vip3Aa1. While both Vip3Aa1 and Vip3Ac1 showed no detectable toxicity against the European corn borer Ostrinia nubilalis, the chimeric protein Vip3AcAa, consisting of the N-terminal region of Vip3Ac1 and the C-terminal region of Vip3Aa1, became insecticidal to the European corn borer. In addition, the chimeric Vip3AcAa had increased toxicity to the fall armyworm. Furthermore, both Vip3Ac1 and Vip3AcAa are highly insecticidal to a strain of cabbage looper (Trichoplusia ni) that is highly resistant to the B. thuringiensis endotoxin Cry1Ac, thus experimentally showing for the first time the lack of cross-resistance between B. thuringiensis Cry1A proteins and Vip3A toxins. The results in this study demonstrated that vip3Ac1 and its chimeric vip3 genes can be excellent candidates for engineering a new generation of transgenic plants for insect pest control.

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Identification of cry1I-Type Genes from Bacillus thuringiensis Strains and Characterization of a Novel cry1I-Type Gene

Applied and Environmental Microbiology ◽

10.1128/aem.69.9.5207-5211.2003 ◽

2003 ◽

Vol 69 (9) ◽

pp. 5207-5211 ◽

Cited By ~ 90

Author(s):

Fuping Song ◽

Jie Zhang ◽

Aixing Gu ◽

Yue Wu ◽

Lanlan Han ◽

...

Keyword(s):

Bacillus Thuringiensis ◽

Diamondback Moth ◽

Leaf Beetle ◽

Beet Armyworm ◽

Universal Primers ◽

Cry Protein ◽

Corn Borer ◽

Pod Borer ◽

Asian Corn Borer ◽

Type Gene

ABSTRACT A PCR-restriction fragment length polymorphism method for identification of cry1I-type genes from Bacillus thuringiensis was established by designing a pair of universal primers based on the conserved regions of the genes to amplify 1,548-bp cry1I-type gene fragments. Amplification products were digested with the Bsp119I and BanI enzymes, and four kinds of known cry1I-type genes were successfully identified. The results showed that cry1I-type genes appeared in 95 of 115 B. thuringiensis isolates and 7 of 13 standard strains. A novel cry1I-type gene was found in one standard strain and six isolates. The novel cry1I gene was cloned from B. thuringiensis isolate Btc007 and subcloned into vector pET-21b. Then it was overexpressed in Escherichia coli BL21(DE3). The expressed product was shown to be toxic to the diamondback moth (Plutella xylostella), Asian corn borer (Ostrinia furnacalis), and soybean pod borer (Leguminivora glycinivorella). However, it was not toxic to the cotton bollworm (Helicoverpa armigera), beet armyworm (Spodoptera exigua), or elm leaf beetle (Pyrrhalta aenescens) in bioassays. Subsequently, the Cry protein encoded by this novel cry gene was designated Cry1Ie1 by the B. thuringiensis δ-endotoxin nomenclature committee.

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