A common plant can provide important hints on how to develop drought-resistant crops in a world plagued by climate change. Yale scientists explain how Portulaca oleracea, also known as purslane, integrates two different metabolic pathways to produce a novel type of photosynthesis that allows the weed to withstand drought while remaining highly productive in a report published in the journal Science Advances.
A common weed contains vital information about how to develop drought-resistant crops in a world beset by climate change. Scientists describe how the weed Portulaca oleracea, also known as purslane, combines two distinct metabolic pathways to produce a novel type of photosynthesis that allows it to withstand drought while remaining highly productive.
In the journal Science Advances, Yale scientists describe how Portulaca oleracea, also known as purslane, integrates two distinct metabolic pathways to create a novel type of photosynthesis that allows the weed to withstand drought while remaining highly productive.
Purslane is unique in that it has both of these evolutionary adaptations, allowing it to be both extremely productive and drought tolerant, which is an unusual combination for a plant. The majority of scientists believed that C4 and CAM worked independently inside purslane leaves.
This is a very rare combination of traits that has created a kind of ‘super plant’ — one that could potentially be useful in endeavors such as crop engineering. There is still a lot of work to be done in terms of engineering a CAM cycle into a C4 crop, such as maize, before that could become a reality.
Erika Edwards
The Yale team, on the other hand, was led by co-corresponding authors and postdoctoral researchers Jose Moreno-Villena and Haoran Zhou. They conducted a geographical investigation of gene expression in purslane leaves and discovered that C4 and CAM activity is completely integrated. They work in the same cells, with the C4 pathway processing CAM byproducts. In times of drought, this strategy provides a C4 plant with unusually high levels of protection.
“This is a very rare combination of traits that has created a kind of’super plant’ — one that could potentially be useful in endeavors such as crop engineering,” said Erika Edwards, professor of ecology and evolutionary biology at Yale and senior author of the paper.
Plants have independently evolved a variety of distinct mechanisms to improve photosynthesis, the process by which green plants use sunlight to synthesize nutrients from carbon dioxide and water. For instance, corn and sugarcane evolved what is called C4 photosynthesis, which allows the plant to remain productive under high temperatures. Succulents such as cacti and agaves possess another type called CAM photosynthesis, which helps them survive in deserts and other areas with little water. Both C4 and CAM serve different functions but recruit the same biochemical pathway to act as “add-ons” to regular photosynthesis.
Purslane is unique in that it possesses both of these evolutionary adaptations, allowing it to be both highly productive and drought tolerant, an unusual combination for a plant. Most scientists believed that C4 and CAM functioned independently within purslane leaves.
However, the Yale team, led by co-corresponding authors and postdoctoral scholars Jose Moreno-Villena and Haoran Zhou, performed a spatial analysis of gene expression within purslane leaves and discovered that C4 and CAM activity are completely integrated. They both work in the same cells, with the C4 pathway processing the products of CAM reactions. In times of drought, this system provides unusual levels of protection for a C4 plant.
The researchers also created metabolic flux models that predicted the emergence of an integrated C4+CAM system, which matched their experimental findings. According to the authors, understanding this novel metabolic pathway could help scientists devise new ways to engineer crops such as corn to withstand prolonged drought.
“There is still a lot of work to be done in terms of engineering a CAM cycle into a C4 crop, such as maize, before that could become a reality,” Edwards said. “However, we have demonstrated that the two pathways can be efficiently integrated and share products. C4 and CAM are more compatible than we previously thought, raising the possibility that there are many more C4+CAM species out there waiting to be discovered.”
