Applied and Environmental Microbiology (2018) 84 (20 - e01393-18)

Isabel Gómez, Josue Ocelotl, Jorge Sánchez, Christina Lima, Erica Martins, Anayeli Rosales-Juárez, Sotero Aguilar-Medel, André Abad, Hua Dong, Rose Monnerat, Guadalupe Peña, Jie Zhang, Mark Nelson, Gusui Wu, Alejandra Bravo and Mario Soberón (2018)
Enhancement of Bacillus thuringiensis Cry1Ab and Cry1Fa toxicity to Spodoptera frugiperda by domain III mutations indicates there are two limiting steps in toxicity as defined by receptor binding and protein stability
Applied and Environmental Microbiology 84 (20 - e01393-18)
Abstract: Bacillus thuringiensis Cry1Ab and Cry1Fa toxins are environmentally safe insecticides that control important insect pests. Spodoptera frugiperda is an important maize pest that shows low susceptibility to Cry1A toxins, in contrast to Cry1Fa, which is highly active against this pest and is used in transgenic maize for S. frugiperda control. The β16 region from domain III of Cry1Ab has been shown to be involved in interactions with receptors such as alkaline phosphatase (ALP) or aminopeptidase (APN) in different lepidopteran insects. Alanine-scanning mutagenesis of amino acids of Cry1Ab β16 (⁵⁰⁹STLRVN⁵¹⁴) revealed that certain β16 mutations, such as N514A, resulted in increased toxicity of Cry1Ab for S. frugiperda without affecting the toxicity for other lepidopteran larvae, such as Manduca sexta larvae. Exhaustive mutagenesis of N514 was performed, showing that the Cry1Ab N514F, N514H, N514K, N514L, N514Q, and N514S mutations increased the toxicity toward S. frugiperda. A corresponding mutation was constructed in Cry1Fa (N507A). Toxicity assays of wild-type and mutant toxins (Cry1Ab, Cry1AbN514A, Cry1AbN514F, Cry1Fa, and Cry1FaN507A) against four S. frugiperda populations from Mexico and one from Brazil revealed that Cry1AbN514A and Cry1FaN507A consistently showed 3- to 18-fold increased toxicity against four of five S. frugiperda populations. In contrast, Cry1AbN514F showed increased toxicity in only two of the S. frugiperda populations analyzed. The mutants Cry1AbN514A and Cry1AbN514F showed greater stability to midgut protease treatment. In addition, binding analysis of the Cry1Ab mutants showed that the increased toxicity correlated with increased binding to brush border membrane vesicles and increased binding affinity for S. frugiperda ALP, APN, and cadherin receptors.
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Link to article at publishers website
Database assignments for author(s): Alejandra Bravo, Jie Zhang

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
genetical engin./transgenic plants

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Spodoptera frugiperda	Maize/corn (Zea mays)	Mexico
Bacillus thuringiensis Cry1A-toxin (entomopathogen)	Spodoptera frugiperda	Maize/corn (Zea mays)	Mexico
Bacillus thuringiensis Cry1F-toxin (entomopathogen)	Spodoptera frugiperda	Maize/corn (Zea mays)	Mexico