Transport of RNA across the cells in plants!

How does a developing plant shoot know how, where, and when to grow? Dividing cells need to pass messages from one another to coordinate growth. In plants, important messages are packaged into RNA, which are sent from cell to cell.

By studying the mustard-like plant Arabidopsis thaliana, a research team found that RNA messages need a special protein to escort them where they need to go. Without this escort, cells cannot coordinate and the plant fails to develop properly. 

Unlike animal cells, plant cells are surrounded by a rigid cell wall. Messages can cross this wall through tiny holes called plasmodesmata. The lead author of the study, says, “Plasmodesmata are nanochannels embedded in the cell wall. They mediate various signals’ transport from cell to cell, including protein, RNA, hormones, ions, and nutrients.”

The KNOTTED1 (KN1) homeodomain family transcription factors act non–cell autonomously to control stem cell maintenance in plants through cell-to-cell movement of their proteins and mRNAs through plasmodesmata; however, the mechanism of mRNA movement is largely unknown.

The authors wondered how the plasmodesmata’s gates regulate messaging from one cell to the next. The team discovered that RNA signaling relied on a protein called AtRRP44a. AtRRP44A can interact with plasmodesmata and mediates the cell-to-cell trafficking of KN1 mRNA, and genetic analysis indicates that AtRRP44A is required for the developmental functions of SHOOT MERISTEMLESS, an Arabidopsis KN1 homolog. 

Lowering the amount of AtRRP44a slowed the movement of RNA messages; lacking the right messages, the plants failed to develop properly.

A protein similar to this escort protein is present in other plants, yeast, and animals. The researchers were able to swap out part of the Arabidopsis thaliana signaling system with parts from corn and restore normal development, showing that this signaling system is similar in many kinds of plants.

The author says, “Plants are very sophisticated. We think of them just sitting in their environment, not moving, but really they’re processing a lot of information. The different parts of the plant are talking to each other, sharing whether they have some pathogen attack or if they need some nutrients.”

In a related study published recently in the journal Science, the authors and collaborators found that signals transported through these gates can increase the number of cell layers in corn roots, making the plants potentially more resilient to environmental changes.