Improving the efficiency of food production is an important concern that is expected to grow in severity in coming years, with nearly half of the freshwater basins in the United States expected to be unable to meet demand in just over 50 years. Using a tool primarily employed in studies of the nervous system, researchers at the University of Glasgow have developed a genetically modified plant that shows promise in improving water use efficiency without compromising carbon dioxide uptake. The tool, called optogenetics, is commonly used to control specific groups of neurons by introducing channels in their outer surfaces that allow charged atoms, or ions, to flow into or out of the cell when a specific colored light of is present. A wide variety of cellular processes depend on the flow of ions, including electrical activity found in the nervous system, the beating of the heart, contraction of muscles, and the means by which cells obtain and store energy from food.
The authors of this study knew that, like neurons, cells in the leaves of plants depend on changes in the number of ions inside the cell to perform important functions. In leaf cells, this includes regulating the uptake of carbon dioxide, an essential step in photosynthesis, the process by which plants convert sunlight into food. Carbon dioxide enters the plant through small openings on the leaf called stoma (sg. stomata). These stoma are surrounded by pairs of guard cells which control the size of the opening, and thus how much carbon dioxide enters, depending on the amount of water and ions found inside the cells. Importantly, while larger stoma allow more carbon to enter the plant, they also provide a route for water to escape. Therefore, the plant must properly balance how much carbon dioxide it needs with how much water it can afford to lose.
These guard cells change the size of the openings depending on various environmental conditions, but the process of changing size is rather slow, taking up to an hour. During this adaptation time, water can be lost if the closing is too slow, and the rate of food production may decrease if the stoma cannot open quickly enough when carbon dioxide levels drop.
By introducing a light-activated channel in these guard cells, the authors showed that leaf stoma can respond more rapidly, and the overall water use efficiency is improved during conditions where light levels and other environmental conditions fluctuate over time. The water use efficiency of the genetically modified plants was approximately 1.5 times higher than the unmodified plants. As these conditions reflect natural scenarios, this genetic tool can potentially be used to improve water efficiency and food production. The channels were added by genetic modification, in which specific sequences of DNA are introduced into all cells within a given region, but the actual proteins made from those genes, in this case, the ion channels, are only expressed in a desired cell type. Thus, genetic modification allows for precise targeting of a desired group of cells without affecting other parts of the organism, making these strategies far more reliable than conventional mutations with a large reduction in the potential for harmful side effects. Clearly, the genetically modified crops must be further tested for safety, but manipulating the response properties of stomata is an important step in developing genetically modified crops, which will be essential in avoiding water shortages. This study also suggests that optogenetics may have far more widespread uses than just studying neurons.
Managing Correspondent: Andrew T. Sullivan
Press Articles: New, more efficient way to reduce water use and improve plant growth, Phys.org
Original Journal Article: “Optogenetic manipulation of stomatal kinetics improves carbon assimilation, water use, and growth,” Science
Image Credit: Pixabay