● `color{violet}("Bt toxin")` is produced by a bacterium called `color{violet}("Bacillus thuringiensis")` (Bt for short).

● `color{violet}("Bt toxin gene")` has been `color{violet}("cloned")` from the `color{violet}("bacteria")`
and been expressed in plants to provide resistance to insects without the need for insecticides; in effect created a
`color{violet}("bio-pesticide")`.

● Examples are `color{violet}("Bt cotton, Bt corn, rice,") `
`color{violet}("tomato, potato")`
and `color{violet}("soyabean")` etc.

● Some strains of `color{violet}("𝘉𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘵𝘩𝘶𝘳𝘪𝘯𝘨𝘪𝘦𝘯𝘴𝘪𝘴")` produce `color{violet}("proteins")` that kill certain insects such as
`color{violet}("lepidopterans (tobacco budworm, armyworm)")`,
`color{violet}("coleopterans (beetles)")` and `color{violet}("dipterans (flies, mosquitoes)")`.

● `color{violet}("𝘉. 𝘵𝘩𝘶𝘳𝘪𝘯𝘨𝘪𝘦𝘯𝘴𝘪𝘴")` forms `color{violet}("protein crystals")` during a particular phase of their
`color{violet}("growth.")`

● These crystals contain a `color{violet}"toxic insecticidal"` protein.

● But this `color{violet}("toxin")` does not `color{violet}("kill the 𝘉𝘢𝘤𝘪𝘭𝘭𝘶𝘴")`.

● Actually, the `color{violet}("Bt toxin protein")` exists as inactive `color{violet}("protoxins")` but once an insect ingest the inactive `color{violet}("toxin")`, it is converted into an active form of `color{violet}("toxin")` due to the `color{violet}("alkaline pH")` of the gut which solubilise the crystals.

● The activated `color{violet}("toxin binds")` to the surface of `color{violet}("midgut epithelial cells")` and create `color{violet}("pores")` that cause `color{violet}("cell swelling")` and `color{violet}("lysis and eventually")` cause `color{violet}("death of the insect")`.



● Specific `color{violet}("Bt toxin genes")` were isolated from `color{violet}("𝘉𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘵𝘩𝘶𝘳𝘪𝘯𝘨𝘪𝘦𝘯𝘴𝘪𝘴")` and incorporated into the several crop `color{violet}("plants")` such as `color{violet}("cotton")`.

● The choice of `color{violet}("genes")` depends upon the crop and the targeted pest, as most `color{violet}("Bt toxins")` are insect-group specific.

● The `color{violet}("toxin")` is coded by a `color{violet}("gene")` named `color{violet}("cry")`.

● There are a number of them, for example, the `color{violet}("proteins encoded by the genes")`

`star` `color{Brown}("𝘤𝘳𝘺𝘐𝘈𝘤")` and `color{violet}("𝘤𝘳𝘺𝘐𝘐𝘈𝘣")` control the `color{violet}("cotton bollworms")`
`star` `color{Brown}("𝘤𝘳𝘺𝘐𝘈𝘣")` controls `color{violet}("corn borer")`.

● Several nematodes parasitise a `color{violet}("wide variety")` of `color{violet}("plants")` and `color{violet}("animals")` including human beings.

● A `color{violet}("nematode 𝘔𝘦𝘭𝘰𝘪𝘥𝘦𝘨𝘺𝘯𝘦 𝘪𝘯𝘤𝘰𝘨𝘯𝘪𝘵𝘪𝘢")` infects the roots of `color{violet}("tobacco plants")` and causes a `color{violet}("great reduction in yield")`.

● A `color{violet}("novel strategy")` was adopted to prevent this infestation which was based on the process of `color{violet}("RNA interference (RNAi)")`.

● `color{violet}("RNAi")` takes place in all `color{violet}("eukaryotic organisms")` as a method of `color{violet}("cellular defense")`.

● This method involves silencing of a specific `color{violet}("mRNA")` due to a complementary `color{violet}("dsRNA")` molecule that binds to and prevents translation of the `color{violet}("mRNA (silencing)")`.

● The source of this `color{violet}("complementary RNA")` could be from an infection by `color{violet}("viruses")` having `color{violet}("RNA genomes or mobile genetic")` elements (transposons) that replicate via an `color{violet}("RNA")` intermediate.

● Using `color{violet}("𝘈𝘨𝘳𝘰𝘣𝘢𝘤𝘵𝘦𝘳𝘪𝘶𝘮 vectors, nematode-specific genes")` were introduced into the `color{violet}("host plant")` .

● The introduction of `color{violet}("DNA")` was such that it produced both sense and anti-sense `color{violet}("RNA")` in the `color{violet}("host cells")`.

● These `color{violet}("two RNA’s")` being complementary to each other formed a `color{violet}("double stranded (dsRNA)")` that `color{violet}("initiated RNAi")` and thus, silenced the specific `color{violet}("mRNA of the nematode")`.

● The `color{violet}("consequence")` was that the `color{violet}("parasite")` could not survive in a `color{violet}("transgenic host expressing specific interfering RNA")`.