Yale researchers describe how Portulaca oleracea, also known as purslane, integrates two distinct metabolic pathways to produce a novel type of photosynthesis that allows the weed to withstand drought while remaining highly productive in the journal Science Advances, which was published on August 5th.
"This is a very rare combination of traits that has created a kind of 'super plant'—one that could potentially be useful in endeavours such as crop engineering," said Erika Edwards, senior author of the paper and professor of ecology and evolutionary biology at Yale.
Plants have evolved a diverse set of mechanisms to improve photosynthesis, the process by which green plants use sunlight to synthesize nutrients from carbon dioxide and water. Corn and sugarcane, for example, evolved C4 photosynthesis, which allows the plant to remain productive in high temperatures.
Succulents, such as cacti and agaves, have another type of photosynthesis known as CAM photosynthesis, which allows them to survive in deserts and other dry areas. C4 and CAM have different functions, but they both use 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."
(Source: Yale University)
