How drought-tolerant grasses came to be

November 23, 2011
Grasses that use the C4 photosynthetic pathway -- like these tufts of Enneapogon scaber from Namibia -- are particularly good at growing in hot, dry environments. Credit: Photo by study co-author J. Travis Columbus, Rancho Santa Ana Botanic Garden and Claremont Graduate University.

If you eat bread stuffing or grain-fed turkey this Thanksgiving, give thanks to the grasses — a family of plants that includes wheat, oats, corn and rice. Some grasses, such as corn and sugar cane, have evolved a unique way of harvesting energy from the sun that's more efficient in hot, arid conditions. A new grass family tree reveals how this mode of photosynthesis came to be.

The results may one day help scientists develop more drought-tolerant grains, say scientists working at the U. S. National Evolutionary Synthesis Center.

From the grasslands of North America, to the pampas of South America, to the steppes of Eurasia and the savannas of the tropics, the grass family contains more than 10,000 species, including the world's three most important crops: wheat, rice and corn. We rely on grasses for sugar, liquor, bread, and livestock fodder.

Like all plants, grasses harvest energy from sunlight by means of photosynthesis. But grasses use two strategies that differ in how they take up carbon dioxide from the air and convert it into the starches and sugars vital to plant growth. The majority of grasses use a mode of photosynthesis called the C3 pathway, but many species — especially those in hot, tropical climates — use an alternate mode of photosynthesis known as C4. In hot, arid environments, C4 grasses such as maize, sugar cane, sorghum and millet have a leg up over C3 plants because they use water more efficiently.

Grasses have been around since the dinosaurs, but despite their economic importance we know little about their history. Credit: Photo by study co-author J. Travis Columbus, Rancho Santa Ana Botanic Garden and Claremont Graduate University.

An international team of researchers wanted to figure out how many times, and when, the C4 strategy came to be. To find out, they used DNA sequence data from three chloroplast genes to reconstruct the grass family tree. The resulting phylogeny represents 531 species, including 93 species for which DNA sequence data was previously unavailable.

"By working collaboratively across many labs, from the US to Argentina to Ireland to Switzerland — with some people providing new plant material, and others doing the DNA sequencing — we were able to get a lot done in a very short amount of time," said co-author Erika Edwards of Brown University.

The results suggest that the C4 pathway has evolved in the grasses more than 20 separate times within the last 30 or so million years, Edwards said.

What's most surprising, she added, is that C4 evolution seems to be a one-way street – i.e., once the pathway evolves, there's no turning back. "We can't say whether it is evolutionarily 'impossible', or whether there simply hasn't been a good reason to do it, but it seems increasingly unlikely that any C4 grasses have ever reverted to the C3 condition," Edwards said.

"The new tree will be extremely useful for anyone who works on grasses," she added.

For example, scientists are currently trying to engineer the C4 photosynthetic pathway into C3 crops like rice to produce more stress-tolerant plants. By helping researchers identify pairs of closely related C3 and C4 species, the evolutionary relationships revealed in this study could help pinpoint the genetic changes necessary to do that.

"The next challenge is getting these species into cultivation and studying them closely, and ideally, sequencing their genomes," Edwards said.

The results will be published this week in the journal New Phytologist.

Explore further: Biologist solves mystery of tropical grasses' origin

More information: Grass Phylogeny Working Group II (2011). "New grass phylogeny resolves deep evolutionary relationships and discovers C4 origins." New Phytologist. doi: 10.1111/j.1469-8137.2011.03972.x

Related Stories

Biologist solves mystery of tropical grasses' origin

February 8, 2010

Around 30 to 40 million years ago, grasses on Earth underwent an epic evolutionary upheaval. An assemblage capitalized on falling levels of atmospheric carbon dioxide by engineering an internal mechanism to concentrate the ...

New research changes understanding of C4 plant evolution

November 15, 2010

(PhysOrg.com) -- A new analysis of fossilized grass-pollen grains deposited on ancient European lake and sea bottoms 16-35 million years ago reveals that C4 grasses evolved earlier than previously thought. This new evidence ...

Key discovered to cold tolerance in corn

August 29, 2008

Demand for corn -- the world's number one feed grain and a staple food for many -- is outstripping supply, resulting in large price increases that are forecast to continue over the next several years. If corn's intolerance ...

Recommended for you

Neanderthal DNA contributes to human gene expression

February 23, 2017

The last Neanderthal died 40,000 years ago, but much of their genome lives on, in bits and pieces, through modern humans. The impact of Neanderthals' genetic contribution has been uncertain: Do these snippets affect our genome's ...

New gene for atrazine resistance identified in waterhemp

February 23, 2017

Waterhemp has been locked in an arms race with farmers for decades. Nearly every time farmers attack the weed with a new herbicide, waterhemp becomes resistant to it, reducing or eliminating the efficacy of the chemical. ...

Arctic 'doomsday' seed vault receives 50,000 new deposits

February 23, 2017

Nearly 10 years after a "doomsday" seed vault opened on an Arctic island, some 50,000 new samples from seed collections around the world have been deposited in the world's largest repository built to safeguard against wars ...

Ball-rolling bees reveal complex learning

February 23, 2017

Bumblebees can be trained to score goals using a mini-ball, revealing unprecedented learning abilities, according to scientists at Queen Mary University of London (QMUL).

New link found between sex and viruses

February 23, 2017

Sexual reproduction and viral infections actually have a lot in common. According to new research, both processes rely on a single protein that enables the seamless fusion of two cells, such as a sperm cell and egg cell, ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.