142. 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:
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

The Effect of miRNA Overexpression on Gene X Expression in Arabidopsis thaliana

MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate gene expression at the post-transcriptional level. miRNAs bind to specific messenger RNAs (mRNAs) and typically induce gene silencing by either degrading the target mRNA or inhibiting its translation. As regulatory molecules, miRNAs play essential roles in controlling various biological processes, including development, stress responses, and metabolism.

In a recent experiment involving Arabidopsis thaliana, it was observed that miRNA A directly targets gene X. Overexpressing miRNA A in this model organism was used to investigate its effect on gene X expression. Based on the regulatory role of miRNAs, the impact of miRNA A overexpression was analyzed, and the following possibilities emerged.

Potential Outcomes of miRNA Overexpression on Gene X

1. Only Transcript Abundance of Gene X Will Be Affected:

   • When miRNA A overexpression occurs, one of the key effects is typically on the mRNA of gene X. miRNAs bind to the target mRNA, leading to its degradation or translational repression. If this happens, we expect a decrease in transcript abundance for gene X. However, this does not necessarily mean that only the transcript level is affected, as protein levels could also change due to translational inhibition.

2. The Resultant Protein X Will Be of Smaller Size:

   • miRNAs typically do not affect the size of the resulting protein. Instead, their primary role is in reducing protein levels by preventing mRNA translation or inducing mRNA degradation. Therefore, overexpression of miRNA A would likely reduce the abundance of protein X but not necessarily alter its size.

3. Only Specific Activity of Protein X Will Get Reduced:

   • miRNA overexpression can certainly reduce the activity of protein X by lowering the protein levels through translational repression. However, it is not guaranteed that miRNA overexpression would only affect protein activity. The reduction in protein levels usually goes hand-in-hand with a reduction in protein activity, as there is less of the functional protein present to carry out its activity.

4. Both Transcript and Protein Abundance of Gene X May Get Reduced:

   • This is the most likely outcome of miRNA overexpression. miRNAs can decrease mRNA levels by inducing degradation or inhibiting translation. As a result, the protein abundance of gene X would also be reduced, since less mRNA would be available for translation. This outcome is consistent with the typical regulatory function of miRNAs.

The Correct Answer

The most accurate statement is:

Answer: D. Both transcript and protein abundance of X may get reduced

This aligns with the general function of miRNAs, which can lead to a reduction in both transcript and protein levels of a target gene due to their role in post-transcriptional regulation.

Conclusion

In the experiment where miRNA A was overexpressed in Arabidopsis thaliana, the primary outcome would be a reduction in both the mRNA and protein levels of gene X. This is due to the mechanism by which miRNAs typically regulate gene expression — by either degrading the mRNA or inhibiting its translation. Therefore, both transcript and protein abundance would be affected, which is a hallmark of miRNA-mediated gene silencing.