When plants grow, their stems, roots and leaves increase in size and abundance in a coordinated manner. The changes in one type of organ keep pace with the changes in the other types. Dividing cells need to communicate with one another in order to achieve this, and previous research has identified that plants package important messages into molecules of RNA, which are sent from cell to cell.
New research, published today in the journal Science, adds to this understanding by identifying a special protein in the cells of plants that acts as an escort and helps the RNA molecules to travel to where they are needed.
By studying the mustard-like plant Arabidopsis thaliana, Cold Spring Harbor Laboratory (CSHL) Professor David Jackson and his team found that without this escort protein, known as AtRRP44a, the plant cells cannot communicate or coordinate the growth of the plant.
While all animal and plant cells are surrounded by a membrane, plant cells alone have an additional wall around each cell. Chemical messages can cross this cell wall through tiny holes called plasmodesmata.
Munenori Kitagawa is a postdoc in the Jackson lab who led the study. He explained that plasmodesmata are nanochannels embedded in the cell wall. “They mediate [the transport of various signals] from cell to cell, including protein, RNA, hormones, ions, and nutrients.”
Kitagawa investigated exactly how plasmodesmata regulate the movement of chemical messages from one cell to the next. He and his colleagues discovered that the protein AtRRP44a is involved in the transport of RNA molecules through the nanochannels in the cell wall. Decreasing the amount of AtRRP44a available slowed down the movement of RNA messages between cells and, because they then lacked the right messages, the plants failed to develop properly.
A protein similar to this escort protein is present in other plants, yeasts, and animals. The researchers were able to swap out part of the Arabidopsis thaliana signaling system and replace it with a part from corn; this restored normal development, showing that many kinds of plants share this signaling system.
“Plants are very sophisticated,” said Jackson. “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.”
“This paper represents an important step towards understanding how information is exchanged between cells to control development and other processes,” said John McDowell, a program officer in the U.S. National Science Foundation’s Directorate for Biological Sciences. “By revealing a new component of cell-to-cell communication, this research opens the door for further investigation that could allow us to harness this process.”