Protein Pathways

We pass them every day on the sidewalk. Chances are they have taken up residence in your home or office. But we don't often pause to reflect on the maturation of plants. Kimberly Gallagher does. The associate professor of biology and her lab explore the mechanisms of intercellular protein movement in plants, and how this form of communication impacts plant growth.

In the recent paper, “The Movement of the Non-Cell-Autonomous Transcription Factor, SHORT-ROOT Relies on the Endomembrane System,” in The Plant Journal, Gallagher and her team examine the transfer of proteins via plant-specific channels called plasmodesmata. In animals, most protein movement occurs via the secretory system, a series of interconnected compartments and pathways that Gallagher says are analogous to a subway system. Plants also secrete proteins, but they can use the secretory pathway in non-conventional ways.

"Imagine a subway car going station to station. It's been thought that these proteins travel throughout the cell in an internal fashion, like the passengers in the subway car would,” says Gallagher. But what her lab has discovered—through the use of plants with protein tracers and an imaging technique which allows for high resolution viewing—is that in plants there is a lot of “hitchhiking” occurring on the outside of these compartments. 

This phenomenon has opened up an entirely new avenue of research in plant and animal biology and will likely lead to a whole new understanding of how the cells use endomembrane compartments and secretory pathways. "I liken it to a coffee shop," says Gallagher. "There are hundreds of proteins within the cell that need to interact. For them to randomly walk around until they bump into a partner would not be an efficient solution. It helps if they have a place to meet up.” Gallagher identifies this meeting place as the cytoplasmic membranes of the secretory and recycling vesicles. Once there, proteins can interact and modify their functions and hence impact development of the plant. 

The protein pathway research her lab is doing could help unlock what Gallagher refers to as the holy grail of green agriculture: creating more efficient plants, especially in dynamic climates. Because all plants differ in the way they convert carbon dioxide during photosynthesis, some are less efficient than others. Most are classified as C3 plants due to the carbon pathway they use to turn carbon dioxide into an organic compound. But some plants, like maize, are classified as C4, which indicates a more efficient processing of carbon during photosynthesis and translates into improved water retention and crop yield. 

Engineering C4 photosynthesis into C3 plants is an internationally recognized goal that requires changes in cell-to-cell communication and development. “The work that’s going on in our lab on the movement of this SHORT-ROOT protein is proving to be a key step in creating a working model for achieving this goal,” Gallagher says. “The potential for new discoveries is huge."