Selective Targeting of Mobile mRNAs to Plasmodesmata for Cell-to-Cell Movement

Area of Science:

• Plant molecular biology
• Cell biology
• RNA trafficking

Background:

• Mobile mRNAs are crucial for non-cell-autonomous functions in plants, moving through the phloem to regulate development.
• The intracellular mechanisms governing the selective sorting and movement of these mobile mRNAs remain largely unknown.

Purpose of the Study:

• To visualize and understand the intracellular trafficking and sorting mechanisms of mobile mRNAs in living plant cells.
• To investigate the role of plasmodesmata (PD) in the cell-to-cell movement of specific mRNAs.

Main Methods:

• Development and optimization of a fluorescence-based mRNA labeling system using bacteriophage MS2 coat protein fused to GFP (MS2-GFP) and MS2 recognition sites.
• Utilized a nuclear localization sequence from FD to reduce cytoplasmic background fluorescence.
• Co-expression with a virus movement protein to target labeled mRNA to PD and live imaging of intracellular translocation.

Main Results:

• The improved MS2-GFP system successfully visualized cytoplasmic fluorescent foci containing labeled mRNA.
• Co-expression with a PD-localized virus movement protein targeted these foci to PD, confirming mRNA presence.
• Ex vivo RNA imaging demonstrated selective targeting of mobile but not nonmobile mRNAs to PD, and real-time imaging suggested shared translocation mechanisms with organelles.

Conclusions:

• Plasmodesmata (PD) targeting represents a critical, selective step in the cell-to-cell movement of mobile mRNAs.
• The study provides new insights into the mechanisms regulating mRNA sorting and intercellular transport in plants.