Common Weeds May Be "Superplants" and Are Key to Drought-resistant Crops

In a world plagued by climate change, a common weed provides important clues on how to cultivate drought-resistant crops.

Scientists at Yale University describe how Portulaca oleracea integrates two different metabolic pathways to produce a novel photosynthesis that allows the weed to tolerate drought while maintaining high yield, they report in Science Advances recently.

"This is a very rare trait combination that creates a 'superplant'—a plant that may be useful in crop engineering," says Erika Edwards, a professor of ecology and evolutionary biology at Yale University and senior author of the paper.

Plants have independently evolved a variety of different mechanisms to improve photosynthesis, which is the process by which green plants use sunlight to synthesize nutrients from carbon dioxide and water. For example, maize and sugarcane have evolved C4 photosynthesis, allowing plants to maintain high yields at elevated temperatures. Fleshy plants such as cactus and agave have another type of CAM photosynthesis, which helps them survive in deserts and other water-deprived areas. C4 and CAM function differently, but absorb the same biochemical pathway as an 'add-on' to conventional photosynthesis.

Portulaca oleracea is unique in that it possesses both evolutionary adaptability—which makes it both highly productive and drought-tolerant, an unlikely combination for a plant. Most scientists believe C4 and CAM operate independently in purslane leaves.

However, a Yale team led by co-corresponding author Jose Moreno-Villena and Haoran Zhou, postdoctoral scholars, performed spatial analysis of gene expression within the leaves of Portulaca oleracea and found that C4 and CAM activities were fully integrated. They operate in the same cells and the products of the CAM reaction are processed through the C4 pathway. This system provides unusual protection for C4 plants during drought.

The researchers also developed metabolic flux models that predicted the emergence of a comprehensive C4 + CAM system that reflected their experimental results.

Understanding this new metabolic pathway could help scientists devise new ways to engineer crops such as corn to help them resist prolonged droughts, the researchers said.

"Introducing the CAM cycle in C4 crops such as maize leaves much work to be done before this becomes a reality." "But we have shown that these two pathways can be effectively integrated and share products. C4 and CAM were more compatible than we thought, which led us to suspect that there were more C4 + CAM species waiting to be discovered."

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