Common weeds can be a “superplant” that holds the key to drought-resistant crops

A common weed holds important clues on how to grow drought-resistant crops in a world ravaged by climate change.

Yale scientists describe how Portulaca oleracea, commonly known as purslane, integrates two distinct metabolic pathways to create a novel mode of photosynthesis that allows weeds to survive drought while remaining highly productive, they report Aug. 5 in the magazine scientific advances.

“This is a very rare combination of traits and has created a kind of ‘superplant’ – one that could potentially be useful in endeavors like crop production,” said Erika Edwards of Yale, professor of ecology and evolutionary biology and senior author of the paper.

Plants have independently evolved a variety of different mechanisms to enhance photosynthesis, the process by which green plants use sunlight to synthesize nutrients from carbon dioxide and water. For example, corn and sugar cane have evolved something called C4 photosynthesis, which allows the plant to remain productive at high temperatures. Succulents like cacti and agaves possess another type called CAM photosynthesis that helps them survive in deserts and other water-poor areas. Both C4 and CAM serve different functions, but recruit the same biochemical pathway to act as “add-ons” to regular photosynthesis.

What makes weed purslane unique is that it possesses both of these evolutionary adaptations – allowing it to be both highly productive and very drought tolerant, an unlikely combination for one plant. Most scientists believed that C4 and CAM worked independently within purslane leaves.

But the Yale team, led by co-corresponding authors and postdocs Jose Moreno-Villena and Haoran Zhou, performed a spatial analysis of gene expression in purslane leaves and found that C4 and CAM activity are fully integrated. They act in the same cells, with products of CAM reactions being processed via the C4 pathway. This system offers unusual protection for a C4 crop in times of drought.

Researchers also created metabolic flux models that predicted the emergence of an integrated C4+CAM system that reflects their experimental findings.

Understanding this novel metabolic pathway could help scientists find new ways to engineer crops like corn to withstand prolonged drought, the authors say.

“In terms of developing a CAM cycle in a C4 crop like corn, there is still a long way to go before this can become a reality,” Edwards said. “But what we have shown is that the two paths can be efficiently integrated and products can share. C4 and CAM are more compatible than we thought, leading us to suspect there are many more C4+CAM species out there waiting to be discovered.”