Abstract
Crops expressing Bacillus thuringiensis (Bt)-derived insecticidal protein genes have been commercially available for over 15 years and are providing significant value to growers. However, there remains the need for alternative insecticidal actives due to emerging insect resistance to certain Bt proteins. A screen of bacterial strains led to the discovery of a two-component insecticidal protein named AfIP-1A/1B from an Alcaligenes faecalis strain. This protein shows selectivity against coleopteran insects including western corn rootworm (WCR). Transgenic maize plants expressing AfIP-1A/1B demonstrate strong protection from rootworm injury. Surprisingly, although little sequence similarity exists to known insecticidal proteins, efficacy tests using WCR populations resistant to two different Cry proteins show that AfIP-1A/1B and mCry3A differ in their mode of action while AfIP-1A/1B and the binary Cry34Ab1/Cry35Ab1 protein share a similar mode. These findings are supported by results of competitive binding assays and the similarity of the x-ray structure of AfIP-1A to Cry34Ab1. Our work indicates that insecticidal proteins obtained from a non-Bt bacterial source can be useful for developing genetically modified crops and can function similarly to familiar proteins from Bt.
Highlights
Western corn rootworm (Diabrotica virgifera virgifera LeConte, WCR) and related Diabrotica species are serious insect pests of maize (Zea mays) production in North America and increasingly in Europe[1, 2]
Activity was observed from strain DDMC-P4G7 that was identified as an Alcaligenes faecalis based on its 16 S rRNA gene sequence
Emerging resistance of insects to transgenic insect control traits based on Bacillus thuringiensis (Bt) proteins highlights the importance of discovering novel insecticidal proteins that may offer additional modes of action that can substitute or complement existing trait genes
Summary
Western corn rootworm (Diabrotica virgifera virgifera LeConte, WCR) and related Diabrotica species are serious insect pests of maize (Zea mays) production in North America and increasingly in Europe[1, 2]. Engineered crops developed with genes of the Bacillus thuringiensis (Bt) insecticidal crystal (Cry) proteins have been commercialized for the control of WCR Maize crops with these Bt proteins are planted widely providing substantial benefits to farmers and the environment by protecting yield potential and reducing the need for conventional insecticide applications[4]. Recent reports of lowered WCR susceptibility to these Cry proteins[6,7,8,9,10] reflect the emergence of insect resistance and underscore the need for useful alternative proteins that are active against WCR One such protein is IPD072Aa from Pseudomonas chlororaphis[11] which demonstrates that non-Bt bacteria, even those that are Gram-negative can be sources of insecticidal proteins useful for transgenic trait development. Our findings show that insecticidal proteins derived from a non-Bacillus source can have properties similar to those of Bt Cry proteins
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