Chemistry, Materials & Packaging
Scientists Looking to Agave, Other Succulents as Model for Engineering Drought-Resistant Plants

As a punishing drought continues to grip California and other areas around the globe, scientists are exploring hardy succulents as a pathway to genetically engineer plants to use less water.

Agave and other succulents such as the prickly pear, pineapple and vanilla have evolved to perform a different kind of photosynthesis that enable their survival in semiarid environments.

Crassulacean acid metabolism (CAM) describes the process these species use to absorb most of their carbon dioxide at night rather than during the day, as most plants (known as C3 and C4 plants) do. This timing difference means less water evaporates off the leaves through transpiration.

CAM plants require between a fifth and a third of the water that C3 and C4 plants need, respectively. Scientists are now exploring ways to identify and transfer the CAM photosynthetic process to other plant species.

As concerns about climate change and drought have risen in recent years, interest in CAM has increased dramatically, says Xiaohan Yang, a staff scientist in the Biosciences Division at Oak Ridge National Laboratory.

“We have a very good idea of what genes are important for CAM species,” Yang told Scientific American. “Right now, we are working on how those genes come together, and then we test their efficiency.”

Last week, Yang and 51 researchers from nine different countries co-authored an article published in the journal New Phytologist that outlines a “roadmap” of what needs to happen in the field in order to further CAM research and engineering. Yang says the article is meant not just for scientists studying CAM, but also for a more general audience to introduce them to this research. The authors also discussed how existing CAM plants could be developed into major crops.

Yang and his colleagues are planning to create a C3 hybrid that will be able to switch to a more water-saving metabolism if exposed to drought or high-salinity conditions. As co-author John Cushman referred to it, they want to make a plant that would have “CAM on demand.”

There is a great deal of research needed to make this happen, according to Cushman.

“The pathways are very complex; you don’t want to re-engineer something until we have a good sense of the blueprint,” he said. “The way these pathways have evolved, there is a concerted set of genes involved ... we don’t think a few changes around the edges will be enough.”

Fortunately, some of these hybrid CAM/C3 plants already exist in nature. Clusia pratensis is what scientists call a “facultative CAM.” With normal rainfall, the Panamanian plant takes in CO2 during the day as it acts like a C3 plant. In dry periods, it begins to take in CO2 at night.

“This is the perfect example in nature that [C3 and CAM] can co-exist in a single plant,” Yan said. “That species is kind of magic.”

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