The climate is changing, and it’s stressing crops in a number of new ways, but work at Washington State University may have uncovered a way to help crops survive in a changing climate.
A team of WSU scientists has discovered a little-understood plant protein that guides development of tiny cellular structures that regulate the flow of sap from roots to shoots. Their work was detailed recently in the journal New Phytologist. Researchers at WSU’s Institute of Biological Chemistry teamed with molecular biologists and crop scientists at WSU, Princeton University and the Université Côte d’Azur to look into a protein called MAP20.
The MAP20 protein was believed to have a role in producing cellulose, which is a key component in plant cell walls, but its physiological function remained a mystery. Using Brachypodium, a grass related to wheat that’s used by researchers to model other grasses, IBC biologist and associate professor Andrei Smertenko worked with Karen Sanguinet, a molecular plant scientist and assistant professor in WSU’s Department of Crop and Soil Sciences. They used experiments to test the protein’s function using genetics, cellular structure analysis, cell biology and biochemistry.
A key clue came from where the protein is chiefly found in plants. The protein is in the developing xylem, which is a system of micro-capillaries that moves water and nutrients up from the roots. MAP20 centers on tiny, specialized cell structures called pits, which are microscopic openings with thin membranes that allow fluids to move from cell to cell.
Pit architecture is laid down in the early stages of plant organ development. Cells that form the vasculature gradually die and become hollow tubes. Sap moves between the dead cells through pits, and its flow depends on pit size and thickness of the pit membrane, a thin layer of carbohydrates and proteins.
The team showed that MAP20 interacts with that network of protein nanotubes called microtubules that determine the size of the pits. Glenn Turner, a researcher in Smertenko’s group in the IBC, used an electron microscope to measure the thickness of pit membranes in both MAP20 mutants and control plants.
According to Turner, the mutants had significantly thinner pit membranes, which points to MAP20’s role in drought resiliency.
Adds Smertenko: “Pit architecture plays an important role in plant response to drought. It can prevent blockages called embolisms that form in the vascular cells under drought conditions. When soil moisture dries out, the xylem micro-capillaries can fill with air bubbles that prevent fluid from moving. Think of it as a highway: If you get a blockage, traffic stops."
Making sense of the research
The researchers wondered what would happen if MAP20 wasn’t present in drought conditions. They found that plants without MAP20 had a much lower survival rate. Knockdown of the MAP20 protein affected development of the vasculature system, which lowered yield and increased susceptibility to drought.
Under normal conditions, plants make large pits with thinner membranes to take advantage of plentiful water. In response to drought, MAP20 helps to make smaller pits and thicker membranes, which prevents embolism.
Smertenko explains that the MAP20 response to drought in an arid climate reduces water movement in the plant. This may mean lower yield, but the plant will survive.
Now that scientists know more about how MAP20 functions, they can learn how it is regulated in other staple crops such as wheat. This could lead to breeding crops with optimal vascular architecture, which could mean better yields in drier climates.
Sanguinet adds, “To feed a changing world, we need to examine all aspects of plant growth and development. We can’t change the weather, but we may be able to control the way plants recover from stress. Understanding the role of MAP20 helps us protect the crops of the future.”
Additional partners in the research included Deirdre Fahy at WSU’s IBC; Rhoda Brew-Appiah, a postdoctoral researcher with WSU’s Department of Crop and Soil Sciences; Raymundo Alfaro-Aco, a scientist at Princeton University; and Janice de Almeida Engler, scientist at the Université Côte d’Azur.
The project was funded in part by grants from USDA, the National Science Foundation, WSU’s Orville A. Vogel Wheat Research Fund, and WSU startup funding.