Characterization of Chimeric Bacillus thuringiensis Vip3 Toxins

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.Insecticidal Bacillus thuringiensis endotoxins have been extensively explored for biological control of insect pests. To date, over 350 B. thuringiensis endotoxins have been identified (3,6,7)

Bacterial Vegetative Insecticidal Proteins (Vip) from Entomopathogenic Bacteria

“…Knowledge of the domains of a protein is of great advantage in the design of chimeric proteins. Despite the lack of information on the tertiary structure of Vip3A proteins, two chimeras have been created by sequence swapping between the vip3Aa and vip3Ac genes with the aim of increasing host specificity (77). These chimeras were created by combining ϳ600 amino acids from the N terminus of one protein and ϳ180 amino acids of the C terminus of the other (Table 5).…”

“…Both populations were very susceptible to Vip3Aa, indicating the absence of cross-resistance between the Vip3Aa and Cry1F proteins (111,112). A study using a different Vip3A protein, Vip3Ac, showed that it was equally toxic to susceptible and Cry1Ac-resistant Trichoplusia ni (Lepidoptera: Noctuidae) strains (77). However, in this case, the resistant strain was slightly less susceptible to Vip3Aa (resistance ratio of 2.1) and to two Vip3A chimeric proteins (resistance ratios of 1.8 and 3.2) (77).…”

Biotechnological Prospects for Engineering Insect-Resistant Plants

“…Single-chain Vip proteins, such as Vip3, are active against lepidopteran larvae, with a broader range of toxicity than individual Cry proteins. Their range of activity can be further extended by protein engineering (Fang et al, 2007). Commercial transgenic plants expressing these proteins are under development (Christou et al, 2006).…”

Integration of Insecticidal Protein Vip3Aa1 into Beauveria bassiana Enhances Fungal Virulence to Spodoptera litura Larvae by Cuticle and Per Os Infection

“…1b). His 6 -tagged Vip3Aa1 expressed in E. coli cells was ϳ92 kDa (7). Immunogold localization confirmed the presence of abundant Vip3Aa1 in the conidial cytoplasm of BbV28, as evidenced by dense colloidal gold particles labeled with the polyclonal antibody and the goat anti-rabbit IgG antibody (Fig.…”