Biotechnology in Agriculture
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Direct answer
Agricultural biotechnology creates genetically modified crops by transferring useful genes, mainly to resist pests and tolerate stresses while cutting pesticide use. Its flagship is Bt cotton, carrying crystal-protein genes (cry genes) from the bacterium Bacillus thuringiensis: the protein is an inactive protoxin that becomes lethal in the alkaline insect gut, where it lyses midgut cells. A second strategy, RNA interference, silences essential nematode genes in tobacco plants by expressing double-stranded RNA, protecting roots from Meloidogyne incognita. India's GEAC regulates the safety of such releases.
What you must remember
- GM crop aims: reduced dependence on chemical insecticides, tolerance to abiotic stresses, reduced post-harvest losses, efficient mineral use and better nutritional quality.
- Bacillus thuringiensis: a soil bacterium whose spores carry crystalline Cry proteins; these are harmless to humans but toxic to specific insect larvae.
- Cry protein activation: the insect swallows the inactive protoxin, and the alkaline pH of its gut converts it into active toxin, which binds the midgut epithelium, swells and lyses the cells, killing the insect.
- Gene specificity: cryIAc and cryIIAb protect against cotton bollworms, while cryIAb targets the corn borer; different cry genes must be chosen for each pest.
- Bt cotton: the cry genes are cloned and inserted into cotton using vector systems such as the Ti plasmid of Agrobacterium tumefaciens; commercial planting in India began in 2002.
- RNA interference: a cellular defence triggered by double-stranded RNA that destroys matching mRNA; in tobacco, dsRNA matching a vital gene of the root-knot nematode Meloidogyne incognita silences that gene and protects the plant.
- Bioethics: the GEAC, India's genetic engineering regulator, judges the validity of GM research and the safety of releasing GM organisms.
Common confusion
The Cry protein is not toxic as eaten by the plant-feeder — it must be activated by the alkaline insect gut, which is why humans with acidic stomachs are unaffected. Also, Bt is used both as a microbial biopesticide spray and as an inbuilt transgene; the exam distinction is between spraying spores and expressing cry genes in the plant. RNAi silences the parasite's message; it does not poison it.
Exam-focused takeaway
NEET-UG asks the source bacterium of cry genes, the mechanism of activation in the alkaline gut, and which cry gene controls which pest — cryIAc and cryIIAb for bollworms, cryIAb for corn borer. RNAi questions centre on Meloidogyne incognita and tobacco, and on dsRNA as the trigger. Statement items test GEAC's role and the purposes of GM crops listed above.
Frequently asked questions
What are cry genes?
Genes of Bacillus thuringiensis coding for crystalline proteins that become insecticidal when activated in the alkaline gut of insect larvae.
How does Bt protein kill an insect but not humans?
The inactive protoxin is activated only by the alkaline pH of the insect midgut, where it lyses epithelial cells; the acidic human stomach does not activate it.
Which cry genes protect cotton from bollworms?
cryIAc and cryIIAb control cotton bollworms, whereas cryIAb is used against the corn borer.
How does RNAi protect tobacco from nematodes?
The plant expresses double-stranded RNA matching a vital Meloidogyne incognita gene; the dsRNA triggers RNA interference that degrades the nematode's mRNA, silencing the gene.
What does GEAC do?
As India's genetic engineering regulator, it assesses GM research proposals and the safety of introducing genetically modified organisms for public use.