Synergism and Antagonism between Bacillus thuringiensis Vip3A and Cry1 Proteins in Heliothis virescens, Diatraea saccharalis and Spodoptera frugiperda

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.

Bacterial Vegetative Insecticidal Proteins (Vip) from Entomopathogenic Bacteria

“…For the antagonism between the Vip3A and Cry1C proteins, Lemes et al (75) hypothesized that a physical interaction of the two proteins impairs the access of the binding epitopes to the membrane receptor. Hetero-oligomer formation with an increased ability for membrane insertion or pore formation was proposed to explain the synergism between Cry1Ac and Cry1Aa (76).…”

Relação entre toxicidade de proteínas Vip3Aa e sua capacidade de ligação a receptores intestinais de lepidópteros-praga

“…Portanto, verifica-se que a etapa de ativação não foi a responsável pela ausência de toxicidade para o inseto. Esses resultados foram consoantes com os estudos de ativação da protoxina Vip3A realizados por Lee et al (2003) com outras espécies de lagartas, e confirmaram que a primeira etapa para a atividade inseticida das proteínas Vip3Aa ocorreu.…”

“…Essas proteínas são ingeridas como protoxinas e processadas em toxinas pelas proteases do intestino do inseto, que se ligam a receptores específicos e causam a lise das células do intestino médio (Lee et al, 2003).…”

Cry Proteins from Bacillus thuringiensis Active against Diamondback Moth and Fall Armyworm

“…PCR profiles observed using universal primers revealed the presence of four groups of toxin genes: cry1, cry2, cry8, and cry9, which seem to be related to the protein pattern observed. Using specific primes, the isolates showed different gene content, whose products may act antagonistically or synergistically to confer the observed differences among the LC 50 obtained (Lemes et al 2014, Wei et al 2015. However, such hypothesis (-) Isolate did not show any bands using specific primers.…”