CBSE · Class 12 · Biology · Biotechnology and its ApplicationsDescribe the principles and applications of RNA interference (RNAi) technology. Explain how this mechanism is utilized to develop nematode-resistant tobacco plants.

Introduction to RNA Interference (RNAi)\nRNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression or translation, typically by neutralizing targeted mRNA molecules. This mechanism is present in all eukaryotic organisms as a method of cellular defense and gene regulation, often referred to as post-transcriptional gene silencing (PTGS).

Principle and Mechanism of RNAi

• Triggering Molecule: The process is initiated by the introduction of double-stranded RNA (dsRNA) that is complementary to the target gene's sequence.
• Dicer Action: An endogenous ribonuclease enzyme called Dicer cleaves the long dsRNA molecules into short, double-stranded fragments known as short interfering RNAs (siRNAs) or microRNAs (miRNAs).
• RISC Complex Assembly: These small fragments are incorporated into a multi-protein RNA-induced silencing complex (RISC).
• Target Degradation: Within the RISC complex, the dsRNA unwinds into single strands. The guide strand directs the complex to bind to the complementary sequence on the target messenger RNA (mRNA).
• Silencing: Once bound, the RISC complex either cleaves the mRNA or prevents its translation into protein, effectively silencing the specific gene.

Application: Development of Pest-Resistant Tobacco Plants

• Nematode Infestation: A parasitic nematode, Meloigogyne incognita, infects the roots of tobacco plants, causing a drastic reduction in agricultural yield.
• Introduction of Specific Genes: Using recombinant DNA technology, specific nematode-specific genes (derived from the parasite itself) were introduced into the host tobacco plant using a suitable vector, such as Agrobacterium tumefaciens.
• Sense and Antisense RNA Generation: The introduction of DNA was planned such that it produced both sense and anti-sense RNA simultaneously in the host plant cells.
• dsRNA Formation: Because the sense and antisense RNAs were complementary to each other, they hybridized to form double-stranded RNA (dsRNA), which triggered the RNAi pathway.
• Protection of the Plant: When the parasitic nematode ingested plant root tissues containing this engineered machinery, the systemic dsRNA entered the nematode's cells. This triggered the parasite's internal RNAi mechanism, silencing essential genes required for its survival and development. As a result, the nematode could not survive in the transgenic plant, leaving the tobacco crop protected.