From Weed to Crop

David Marks is driving an effort to domesticate Pennycress with an eye to reducing agricultural runoff and providing a new source of biofuel.
May 23, 2016

For decades Minnesota farmers have weeded a seedy plant known as pennycress from their fields so it wouldn’t compete with corn, soybeans and other cash crops. Now, a group of scientists from the University of Minnesota is not only calling a truce — but working to turn the former foe into an environmental hero that can protect water quality, provide food for honeybees and other pollinators, and serves as a new, lucrative source of oils for biofuel use and human consumption.

Known as pennycress, this knee-high Eurasian native first came to the United States hundreds of years ago, likely as an inadvertent hitchhiker with food plants brought from the old country. Not particularly invasive, it was nonetheless persistent, and gradually spread through much of the cultivated United States, holding its own through its ability — unusual for an annual flowering plant — to sprout in the fall, remain green through the most severe winters, and pick up growing where it left off as soon as snow melts in the spring.

That trait is what caught the eye half a dozen years ago of a team of University of Minnesota scientists led by agronomist Don Wyse who were looking for ways to help keep soil and nutrients on the land rather than letting them run off fields with meltwater and April showers and pollute streams and other waterways. What if, Wyse and colleagues wondered, we could turn pennycress into a crop that produces marketable products, then grow it in the temporal gap between fall harvest and spring planting? Not only could it hold soil and fertilizer in place, it could also provide another source of income during a period fields normally remain unproductive.

Wyse was in luck. Just across campus, at the College of Biological Sciences, David Marks, a top expert in the genetics of Arabidopsis, a close relative of pennycress has served as the lab rat of the plant world since it became the first plant to be genetically sequenced in the 1990s.

Soon Marks found himself signed on for a daunting job: applying his knowledge of Arabidopsis genomics to, in his words, “domesticate pennycress into a new oilseed crop that can be grown during the barren period and that produces an energy-rich oilseed cash crop.”

Most crops we rely on today for food, fuel and fiber became useful over thousands of years as generations of farmers and plant breeders preferentially chose and propagated individuals with traits — big fruits, fast development, and so on — desirable for our human purposes. Marks’ assignment was to apply modern genomics to get pennycress to do more of what makes it beneficial and less of what makes it a bother in a matter of years rather than millennia.

The first step was to sequence the pennycress genome, then compare it with the well-known genome of Arabidopsis and use that comparison to pinpoint which pennycress genes needed tweaking for the plant to take on  new traits..

“Work in Arabidopsis has shown that many mutations result in what can be considered to be agronomically valuable phenotypes — for example, mutations in single genes in Arabidopsis can result in earlier flowering, higher seed yields, bigger seeds, more nutritious seeds and so on,” Marks says. “This provides us with a road map on how to change pennycress from a weed into a new domesticated crop species.”

He’s also using an approach called mutation breeding, which involves using chemical mutagens to induce genetic changes, observing how the traits of offspring differ from those of the parent, and selecting plant lines that show improvements in desirable traits.

“We have been able to isolate many pennycress mutants with the desired phenotypes as predicted from our knowledge of Arabidopsis biology,” Marks says. Plant lines he’s already developed — with the help of CBS undergraduate students — show better stand establishment, early flowering, reduced seed shatter, larger seeds, high yields, and less susceptibility to falling over.

When the snow melted this past spring and the pennycress planted last fall began to show the traits the team’s been selecting for, Marks was delighted. “Seeing genetically stable early-flowering plants in the field has greatly boosted my enthusiasm,” he says.

Next steps for Marks include “stacking” desirable traits in a single plant line and back-crossing plants with desirable traits to eliminate other less desirable traits they picked up in the process. And then, of course, there’s figuring out farm machinery to plant and harvest the new crop, developing markets, and all the other things that go into advancing a new crop to the commercial stage. But all in all, Marks is optimistic that this research will soon lead to exciting new opportunities for farmers to protect their soil while boosting their income.

“Here in Minnesota we have a team of researchers who are successfully breaking down all of these obstacles in parallel,” Marks says. “I think that in five years we will start to see pennycress in the field.” — Mary Hoff

“We have been able to isolate many pennycress mutants with the desired phenotypes as predicted from our knowledge of Arabidopsis biology.”