109. Which one of the following is associated with RNA-induced gene silencing in plants?
(1) DNA methylation
(2)DNA acetylation
(3) DNA degradation
(4) DNA restriction

Detailed Explanation:

Question:
Which one of the following is associated with RNA-induced gene silencing in plants?

Correct Answer:
(1) DNA methylation

What is RNA-Induced Gene Silencing in Plants?

RNA-induced gene silencing, often referred to as RNA interference (RNAi) or post-transcriptional gene silencing (PTGS) in plants, is a natural regulatory process that uses small RNAs to silence specific genes. This process is vital for:

• Defending against viruses

• Regulating gene expression

• Controlling transposable elements

DNA Methylation – The Epigenetic Link

DNA methylation involves the addition of a methyl group (–CH₃) to cytosine residues in DNA, typically at CpG sites. This modification can block transcription factors or recruit proteins that compact the chromatin, thereby silencing gene expression.

In the context of RNA-induced gene silencing:

• Small interfering RNAs (siRNAs) guide the methylation machinery to specific DNA sequences.

• This results in transcriptional gene silencing (TGS) by methylating promoter regions.

• Especially in RNA-directed DNA methylation (RdDM), small RNAs direct methylation to matching DNA sequences.

Thus, RNA-induced gene silencing is tightly connected with DNA methylation, making it a powerful tool in epigenetic regulation.

Why the Other Options Are Incorrect

• (2) DNA acetylation: Typically associated with activation of gene expression.

• (3) DNA degradation: Not a regulated or controlled mechanism for gene silencing.

• (4) DNA restriction: Refers to enzymatic cutting of DNA, mainly in prokaryotes.

Real-World Applications in Plants

• Virus-resistant crops: RNAi pathways target viral genomes.

• Transgenic plants: Gene silencing is used to suppress undesirable traits.

• Epigenetic breeding: DNA methylation patterns can be inherited and used to select favorable traits.

Conclusion

RNA-induced gene silencing is a sophisticated defense and regulatory system in plants, and it operates largely through DNA methylation. This epigenetic mechanism ensures specific genes are turned off at the right time, contributing to plant health, development, and stress responses.

✅ Correct Answer: (1) DNA methylation