Controlled RISC loading efficiency of miR168 defined by miRNA duplex structure adjusts ARGONAUTE1 homeostasis.

Area of Science:

• Plant molecular biology
• RNA biology
• Gene regulation

Background:

• Micro RNAs (miRNAs) are key regulators processed from precursor RNAs.
• ARGONAUTE1 (AGO1) is central to the miRNA pathway, with its expression regulated by miR168.
• Previous work indicated restricted AGO1 loading of miR168, causing cytoplasmic accumulation.

Purpose of the Study:

• To investigate how the intrinsic RNA secondary structure of the MIR168a precursor influences miR168 processing and AGO1 loading.
• To determine if modifying precursor structure affects miR168 loading efficiency.
• To elucidate the role of this mechanism in the dcl1-9 mutant and propose a new model for miR168 action.

Main Methods:

• Analysis of MIR168a precursor secondary structure.
• In vitro and in vivo assays to assess AGO1 loading efficiency.
• Mutational analysis of MIR168a precursor structure.
• Expression studies in wild-type and dcl1-9 mutant plants.

Main Results:

• The secondary structure of the MIR168a precursor precisely controls miR168 processing and AGO1 loading efficiency.
• Alterations in the miRNA duplex structure or artificial precursors modify miR168 loading.
• In the dcl1-9 mutant, enhanced miR168 loading facilitates the elimination of unloaded AGO1 proteins.
• A surplus of miR168 acts as a molecular buffer for AGO1 loading.

Conclusions:

• The intrinsic RNA secondary structure of MIR168a is a critical determinant of miR168 biological activity.
• A novel competitive loading mechanism model is proposed, where miR168 surplus buffers AGO1 loading.
• This mechanism dynamically adjusts AGO1 protein levels in response to cellular miRNA pool fluctuations.