As human-caused climate change drives temperatures higher over the course of the century, the Intergovernmental Panel on Climate Change (IPCC) predicts droughts will likely become longer and more severe. If they are successful and CAM plants are productive enough, the research could potentially have a significant impact on global food security. Tougher plants for a tough global food problem “Right now, we are working on how those genes come together, and then we test their efficiency.” “We have a very good idea of what genes are important for CAM species,” Yang said. Since the genomes of a number of different CAM plants have been sequenced in the past two years, researchers are beginning to develop a better understanding of how the pathway works. The challenge for researchers like Yang is to find a way to get other plants to create this nocturnal carbon storage. At this point, the plant is able to perform photosynthesis like a C3 plant, except the stomata don’t have to stay open because the carbon is already available in the leaf. When the sun rises, the plants break down the organic acids, releasing the CO2. They do this by temporarily fixing carbon in a transient pool of mostly malic acid. However, CAM plants also need a way of storing carbon overnight, because just like other plants, they cannot use it to build energy reserves like sugars and starches without sunlight. In fact, CAM plants require between a fifth and a third of the water that C3 and C4 plants need, respectively. This timing shift means less water evaporates off of the leaves through transpiration. What makes photosynthesis in agave and cactus so different? Unlike most plants that take up carbon dioxide through stomata in their leaves during the day (known as C3 and C4 plants), CAM plants absorb most of their CO2 at night. He said interest in CAM has increased rapidly in the last few years alone, as concern about the effects of climate change on drought has gone up and more funding from the federal government has come in. Xiaohan Yang, a staff scientist in the Biosciences Division at Oak Ridge National Laboratory, is one of the researchers working to figure out how to get CAM to work in other types of plants. Altogether, that could involve somewhere around 100 genes, the researchers said, though they don’t know the exact number yet. Once scientists figure out all the genes associated with its basic function, as well as its regulation, they then have to find a way to add that genetic material into the target plant, or make existing genes and proteins within the plant work the way they want them to. Re-creating an entire metabolic pathway in a plant is far from a simple task. However, it has only been in the last couple of years that a growing number of researchers have been attempting to fully identify and transfer this photosynthetic pathway to other plant species. The process is called crassulacean acid metabolism, or CAM, and a small group of scientists have been studying it for several decades because the plants that have it use less water. The hardy succulent, along with species like prickly pear (an edible cactus), pineapple and vanilla orchids, has evolved over millions of years to perform a different kind of photosynthesis that allows the plants to survive in semiarid environments where water isn’t always readily available. Agave may be most associated with tequila, but this plant has a less familiar use-it’s teaching scientists about how to craft more drought-resistant plants.
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