Synergism and antagonism between Bacillus thuringiensis Vip3A and Cry1 proteins in Heliothis virescens, Diatraea saccharalis and Spodoptera frugiperda.

Ana Rita Nunes Lemes,Odair Aparecido Fernandes,Paula Cristina Brunini Crialesi Legori,Camila Chiaradia Davolos,Juan Ferré,Manoel Victor Franco Lemos,Janete Apparecida Desiderio,Adam Driks

doi:10.1371/journal.pone.0107196

Ana Rita Nunes Lemes, Odair Aparecido Fernandes + Show 6 more

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https://doi.org/10.1371/journal.pone.0107196

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Abstract

Second generation Bt crops (insect resistant crops carrying Bacillus thuringiensis genes) combine more than one gene that codes for insecticidal proteins in the same plant to provide better control of agricultural pests. Some of the new combinations involve co-expression of cry and vip genes. Because Cry and Vip proteins have different midgut targets and possibly different mechanisms of toxicity, it is important to evaluate possible synergistic or antagonistic interactions between these two classes of toxins. Three members of the Cry1 class of proteins and three from the Vip3A class were tested against Heliothis virescens for possible interactions. At the level of LC50, Cry1Ac was the most active protein, whereas the rest of proteins tested were similarly active. However, at the level of LC90, Cry1Aa and Cry1Ca were the least active proteins, and Cry1Ac and Vip3A proteins were not significantly different. Under the experimental conditions used in this study, we found an antagonistic effect of Cry1Ca with the three Vip3A proteins. The interaction between Cry1Ca and Vip3Aa was also tested on two other species of Lepidoptera. Whereas antagonism was observed in Spodoptera frugiperda, synergism was found in Diatraea saccharalis. In all cases, the interaction between Vip3A and Cry1 proteins was more evident at the LC90 level than at the LC50 level. The fact that the same combination of proteins may result in a synergistic or an antagonistic interaction may be an indication that there are different types of interactions within the host, depending on the insect species tested.

Highlights

Bioinsecticides based on Bacillus thuringiensis Berliner are an alternative to chemical insecticides to control important agricultural pests and account for almost 95% of the total sales within the biopesticide market [1]
One important application of the genes that encode insecticidal proteins from this bacterium is their introduction into plants, which has allowed for the development of transgenic plants that are resistant or tolerant to insect pests
At the level of LC90, the three Vip3A proteins were considerably more active than Cry1Aa and Cry1Ca and not significantly different from Cry1Ac. This difference in relative activity at the LC50 and LC90 levels is due to the difference in the respective slopes of regression lines between Cry1 and Vip3A proteins

Summary

Introduction

Bioinsecticides based on Bacillus thuringiensis Berliner are an alternative to chemical insecticides to control important agricultural pests and account for almost 95% of the total sales within the biopesticide market [1]. One important application of the genes that encode insecticidal proteins from this bacterium is their introduction into plants, which has allowed for the development of transgenic plants that are resistant or tolerant to insect pests. Bacillus thuringiensis produces two major categories of active proteins, Cry and Vip. Cry proteins (encoded by cry genes) are produced during the sporulation phase of the bacterium. Vip proteins are produced during the vegetative growth phase of the bacterium and are secreted into the culture medium and have no sequence homology with Cry proteins [2]

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