Table 2.
Modifications made to Bt toxins to improve their efficacy.
| Type of Modification | Bt Toxin | Target Insect | Increase or Decrease in Toxicity | Reference |
|---|---|---|---|---|
| Domain exchanges | ||||
| Domain III Exchange For Domain III of Cry1Ab. |
mCry3Aa | Diabrotica virgifera | The toxicity increased ≥19%. | [58] |
| Domain III, II, I Exchange For Domains of Cry1Ac. |
Cry9Aa | Helicoverpa armigera | The toxicity increased between 4.9 and 5.1 times, concerning parentals. | [59] |
| Domain III Exchange For Domain III of Cry1Ca. |
Cry1Ab; Cry1Ac; Cry1Ba; Cry1Ea; Cry1Fa | Spodoptera exigua | Increased up to 5.5 times for Cry1Fa. | [60] |
| Domain III Exchange For Domain III of Cry1CAc |
Cry1Ca; Cry1Fb; Cry1Ba; Cry1Da; Cry1Ea | Heliothis virescens | The toxicity increased 172 and 69.6 times more for Cry1Ca and Cry1Fb, respectively. | [61] |
| Domain exchanges of Domains II and III, between Cry1Ia and Cry1Ba. | Cry1Ia; Cry1Ba | Leptinotarsa decemlineata | The toxicity increased up to 1127 and 4.2 times, compared to Cry1Ba and Cry1Ia, correspondingly. | [62] |
| Site-directed mutagenesis | ||||
| Loops 1, 2, and 3, domain II substitution. |
Cry4Ba | Culex pipiens; Culex quinquefasciatus | The toxicity increased up to 700 times. | [63] |
| Loops 1 and 2 domain II substitution |
Cry19Aa | Aedes aegypti | The toxicity increased up to 42,000 times, concerning the parental. | [64] |
| Substitution in the domain II | Cry2Ab | Anopheles gambiae | The toxicity increased up to 6.75 times. | [65] |
| Loops 1 and 2 domain II substitution and deletions. |
Cry1Aa | Culex pipiens | Change in insect target. | [66] |
| Substitution in the domain III | Cry1Ab | Spodoptera frugiperda | The toxicity increased up to 44 times, correspondingly to the parental. | [67] |
| Truncated toxins | ||||
| Truncation and selection of mutants, derived from a phage library | Cry1Ia | Telchin licus | The toxicity increased, showing mortality of 50% for approach. | [68] |
| Helix α-1 domain I truncation. | Cry1A | Pectinophora gossypiella | The toxicity increased up to 100 and 150 times for Cry1Ab and CryAc, respectively. | [69] |
| Helix α-1 domain I truncation. | Cry1A | Plutella xylostella; Ostrinia nubilalis | The toxicity increased ≥350 times, against resistant insects. | [70] |
| C-terminal truncation | Cry1C | Spodoptera exigua | The toxicity increased up to 4 times. | [71] |
| Phage-display library | ||||
| Selection of mutant toxins from a phage-display library based on their potential of binding. | Cry1Aa | Bombyx mori | Increased the receptor affinity potential up to 16 and 50 times more, contrasting the parentals. | [72] |
| Selection of mutant toxins from a phage-display library based on their potential of binding. | Cry8Ka | Anthonomus grandis | Increased the toxicity up to 3.2 times, contrasting the parental. | [73] |
| Selection of mutant toxins from a phage-display library based on their potential of binding in the domain II. | Cry1Aa | Nilaparvata lugens | The toxicity increased between 1.4 and 8.9 times, concerning parentals. | [74] |