100-million-year-old molecular 'bypasses' may have helped grasses dominate landscapes and agriculture

About 100 million years ago, before human influence, ancestors of modern grasses, including staple crops like wheat, rice, and maize, evolved specialized metabolic routes in their cells. These "metabolic bypasses," as described in a new study published in Science on August 20, enhanced the efficiency of two crucial compounds: lignin and starch. This discovery offers insights into why grasses and cereal grains dominate natural landscapes and agricultural fields today.

Researchers from the University of Wisconsin–Madison, led by botany professor Hiroshi Maeda, collaborated with scientists worldwide to investigate the origins of grass success. They focused on grass metabolism, specifically genes involved in starch and lignin production. Grasses are well-known for their high starch content, which serves as an energy reserve, and their rapid growth requires efficient lignin production, a key structural component of plant tissues.

To trace the evolutionary history of these traits, the researchers compared the genomes of Joinvillea ascendens, a close relative of grasses that grows slowly in South Pacific forests, with those of three related species. Joinvillea possesses only one pathway for starch synthesis, while all grasses have developed an additional route.

This extra pathway enables grasses to produce twice as much energy as Joinvillea and other non-grass plants, providing them with a significant advantage in rapid growth and competition for sunlight in open habitats.

Moreover, the study uncovered that grasses and Joinvillea both have two pathways for lignin synthesis. Unlike woody plants that grow slowly with high lignin content, grasses can grow rapidly despite their relatively high lignin levels. By analyzing the DNA of these plants, the researchers identified two mutations that created this dual lignin pathway.

This finding suggests that the unique grass trait could be introduced into other crops through genetic modifications, potentially enhancing their energy reserves, structural strength, and resilience.

Understanding these evolutionary innovations could lead to improvements in cereal and bioenergy crops, offering new avenues for sustainable agricultural practices. The researchers are now applying this knowledge to develop strategies for enhancing the productivity and robustness of various plant species.