# DBT JRF 2022 — Question 76

Exam: DBT JRF 2022 · Section: B · Topic: Plant Biology › miRNA Regulation in Plants · Difficulty: Medium

## Question

miRNAs are major regulators of gene expression. In an experiment, it was observed that gene 'X' is a direct target of miRNA 'A'. Upon overexpression of miRNA 'A' in Arabidopsis thaliana:

## Options

- **A.** only transcript abundance of X will be affected
- **B.** the resultant protein X will be of smaller size
- **C.** only specific activity of protein X will get reduced
- **D.** both transcript and protein abundance of X may get reduced

## Answer

Option D

## Explanation

Plant miRNA functions: mRNA cleavage and translational inhibition: Plant miRNAs act through two main mechanisms: 1. Target mRNA cleavage: Plant miRNAs generally have near-perfect complementarity to their targets → RISC-mediated endonucleolytic cleavage of the mRNA → reduced mRNA levels. 2. Translational repression: Less dominant in plants compared to animals, but can occur with imperfect base-pairing. Consequence of overexpressing a miRNA targeting gene X: • Overexpression → MORE miRNA → MORE RISC-miRNA complexes targeting gene X mRNA. • Increased cleavage of gene X mRNA → REDUCED mRNA abundance. • Reduced protein translation from remaining mRNA. • Net result: BOTH mRNA and protein levels of gene X decrease. Answer: Overexpression of miRNA 'A' reduces both mRNA levels (via cleavage) and protein levels of target gene X.

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