This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: 100 million years ago, long before human intervention, ancestors of grasses, including wheat, rice and maize, developed "bypasses" in chemical pathways used to create two critical compounds: lignin and starch. These more efficient pathways could explain why grass plants are so successful in nature and agriculture, according to a new paper published in Science on Aug. 20 by researchers from the University of Wisconsin–Madison and their collaborators.
Like a beltway that creates more flexible traffic flow in a city, these metabolic bypasses led to efficient and robust synthesis of lignin and starch, chemical compounds critical for plants. Grasses and cereal grains make up the majority of global human caloric intake. However, it remains a mystery how these grasses became dominant and successful in nature and agriculture.
The lab of Hiroshi Maeda, a professor of botany at UW–Madison, teamed up with researchers from around the world to address this question. The team was particularly interested in grass metabolism, focusing on genes needed to make starch and lignin. Grasses are rich in starch, a complex carbohydrate that acts as the plant's energy store, and their rapid growth requires the efficient production of lignin, a major component of plant biomass.
Just as scientists use the chimpanzee genome as a comparison tool to study how humans evolved, Maeda's group and their collaborators, including James Leebens-Mack from the University of Georgia, turned to the closest relatives of grasses, such as Joinvillea ascendens. This long-leafed plant is found in wet forests on South Pacific islands and grows much more slowly than many grasses. Only two of more than 100 seeds obtained from the National Tropical Botanical Garden in Hawaii initially germinated.
It took another two years for these plants to grow large enough to be harvested for genomic sequencing. The researchers then sequenced the genomes of Joinvillea and three related species. Comparing thousands of genes found in these genomes, the researchers revealed that Joinvillea has only one pathway to create starch.
All grasses, though, have two. This means that an additional starch synthesis pathway, or bypass route, emerged in the common ancestor of all grasses and now allows grasses to produce twice the amount of energy as Joinvillea and other nongrass plants. In the natural world, a seed with more energy packed inside can germinate, emerge from the ground and begin photosynthesis sooner.
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