Pest-Resistant Plants Using RNA Interference (RNAi)
Biology · Biotechnology and Its Applications · NEET
A pest-resistant plant is made by putting a nematode gene into the plant using an Agrobacterium vector, but in a special way: the plant makes both a sense RNA and an anti-sense RNA. These two pair up to form double-stranded RNA (dsRNA), which triggers RNA interference (RNAi) and silences the nematode's own mRNA. So the pest cannot survive in the plant. Memory hook: "The plant feeds the nematode a poison recipe (dsRNA) that shuts off the pest's own gene."
RNAi pest resistance: Agrobacterium delivers nematode genes; the plant makes sense + anti-sense RNA that pair into dsRNA; RNAi silences the nematode's mRNA so the pest (Meloidogyne incognita, a root parasite of tobacco) cannot survive.
Your doubts, answered
Is this the same as Bt cotton? Both are pest resistant, so are they the same mechanism?
No. They are two totally different strategies and NEET loves to mix them up. Bt cotton uses a toxin PROTEIN (Cry protein from Bacillus thuringiensis) that kills insect pests when they eat the plant. The RNAi method uses NO toxin protein at all. Instead the plant makes dsRNA that silences a gene inside the nematode, so the nematode cannot survive. Bt = protein toxin against insects; RNAi = gene silencing against nematodes.
Which nematode is this and which part of the plant does it attack?
The nematode is Meloidogyne incognita. It infects the ROOTS of tobacco plants and causes a great reduction in yield. NEET 2016 asked exactly this: the answer is the root. Remember: Meloidogyne means 'root-knot' nematode, so root is the target.
How does the plant make double-stranded RNA (dsRNA)? RNA is usually single-stranded.
Nematode-specific genes are introduced so that the plant produces BOTH a sense RNA and a complementary anti-sense RNA. These two single strands are complementary, so they base-pair with each other and form dsRNA. This dsRNA is what starts RNAi. So the plant's own transgene design forces two RNA strands to pair up.
What exactly gets silenced, the plant's gene or the pest's gene?
The PEST's (nematode's) specific mRNA is silenced. The dsRNA made by the plant is complementary to the nematode's mRNA. When the nematode takes up this material, RNAi degrades or blocks translation of that mRNA. The pest gene is switched off, the parasite cannot survive, and the transgenic plant is protected. The plant itself is not harmed.
Which vector is used to put the genes into the plant?
Agrobacterium vectors are used to introduce the nematode-specific genes into the host plant. Agrobacterium tumefaciens naturally transfers DNA into plant cells, so it is the standard delivery tool for making transgenic plants in NCERT.
⚠️ The NEET trap ✗ RNAi pest-resistant plants work by making a toxin protein that poisons the nematode, just like Bt cotton. ✓ RNAi works by gene silencing, not by any toxin protein. The plant makes dsRNA that silences the nematode's specific mRNA. It is a method of cellular defence found in all eukaryotes. Bt cotton is the one that uses a toxin protein. 🧠 Toxin protein = Bt. dsRNA silencing = RNAi. If the question says 'silencing' or 'dsRNA', it is RNAi, never Bt.
Real NEET questions
NEET 2016
Which part of the tobacco plant is infected by Meloidogyne incognita?
A · Flower
B · Leaf
C · Stem
D · Root ✓
Solution: The nematode Meloidogyne incognita parasitises tobacco plants by infecting their ROOTS, causing a great reduction in yield. Resistance is engineered using RNA interference (RNAi), which silences the nematode's specific mRNA using dsRNA, protecting the transgenic plant.
NEET 2019
In RNAi, the genes are silenced using:
A · ds-RNA ✓
B · ss-DNA
C · ss-RNA
D · ds-DNA
Solution: RNA interference silences a specific mRNA using a complementary double-stranded RNA (dsRNA) molecule that binds the target mRNA and prevents its translation. In the nematode-resistance strategy, the sense and anti-sense RNAs pair to form this dsRNA. So genes are silenced using ds-RNA.
NEET 2020
Match Column-I with Column-II: (a) Bt cotton (b) Adenosine deaminase deficiency (c) RNAi (d) PCR; Column-II: (i) Gene therapy (ii) Cellular defence (iii) Detection of HIV infection (iv) Bacillus thuringiensis
A · (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
B · (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
C · (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii) ✓
D · (a)-(iii), (b)-(ii), (c)-(i), (d)-(iv)
Solution: Bt cotton uses the toxin gene of Bacillus thuringiensis (a-iv). The first gene therapy treated ADA deficiency (b-i). RNAi is a method of cellular defence in eukaryotes (c-ii). PCR detects HIV in suspected AIDS patients (d-iii). This gives a-iv, b-i, c-ii, d-iii.
Solved Biotechnology and Its Applications NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
To make the plant resistant to a pest (the nematode Meloidogyne incognita) without using any pesticide, by silencing a gene the pest needs to survive.
Is RNAi natural or artificial?
RNAi is a natural process. It occurs in all eukaryotic organisms as a method of cellular defence. Scientists simply use this natural mechanism to protect crops.
What is the source of dsRNA in nature according to NCERT?
The complementary RNA can come from infection by viruses with RNA genomes, or from mobile genetic elements (transposons) that replicate through an RNA intermediate.
Why can't the nematode survive in the transgenic plant?
The dsRNA made by the plant silences the nematode's specific mRNA. Without that protein, the parasite cannot survive inside the transgenic host, so the plant is protected.
How is this different from Bt cotton for NEET?
Bt cotton uses a toxin protein (Cry protein) to kill insect pests. RNAi uses dsRNA to silence a nematode gene. Different target (insect vs nematode) and different mechanism (protein toxin vs gene silencing).
