The lessons of mutant plants

Joanne Chory sheds light on the mysteries of plant development

Joanne Chory, winner of the 2018 LAS Alumni Achievement Award.
Joanne Chory, winner of the 2018 LAS Alumni Achievement Award.

Joanne Chory’s approach to plant genetics has been described as “letting the mutants lead.”

Chory (MS, ’80; PhD ’84; microbiology) is considered one of the country’s leading plant geneticists, and it was her use of mutant species, grown in total darkness, that led to her first breakthrough discovery in 1989, revealing how plants respond to light at the cellular level.

Since then, her use of mutant strains of the small flowering mustard plant, Arabidopsis thaliana, has led to a cascade of other discoveries on plant growth, development, and cellular structure. Her lab creates mutations and then observes the effects. Does the plant grow faster or taller? Does it need less water? Does it stop sending new shoots toward the sun?

But “letting the mutants lead” is only part of the picture. Chory is a leader in her own right at the Salk Institute, where she directs the Harnessing Plants Initiative. With this innovative program, Chory and her colleagues hope to develop plants that better sequester carbon dioxide in their roots. The idea is to dramatically reduce the amount of CO2 being released into the atmosphere— the primary culprit behind the world’s changing climate.

If their approach works, and if growers embrace such crops, this initiative could have a global impact, she said.

Chory’s work on plant development has earned her many accolades, including the 2018 Breakthrough Prize in Life Sciences, a prestigious award founded by Silicon Valley entrepreneurs, including Facebook’s Mark Zuckerberg.

Most recently, she is a 2018 LAS Alumni Achievement Award winner.

Chory grew up just north of Boston as the third oldest in a family of six children, with three younger brothers who constantly tested her mettle. Her family was strong in the sciences, but Chory said she wasn’t sure about her future path until her passion for the life sciences was ignited at Oberlin College. That’s where she received her undergraduate degree in 1977 before coming to the University of Illinois in microbiology.

The lessons she learned in her big Boston family helped her when she worked in Stan Kaplan’s laboratory at Illinois—which she said often functioned like a large family.

“I understood the process of getting along with people,” she said.

Today, Chory uses this skill as head of a lab at the Salk Institute in La Jolla, California, which she joined in 1988. La Jolla is on the ocean, explaining why some of her “lab equipment” includes surfboards piled up against the wall.

Chory’s first breakthrough was the discovery of a single gene that prevents plants from growing when they are in the dark. Her lab created a mutant plant, in which this gene was knocked out. As a result, the plants began growing in total darkness—reacting as if they were in the light.

“This is a pretty dumb thing for plants to do because they will put their leaves out too soon, while still underground,” Chory explained.

This discovery initially met with skepticism because she said, “People said this is a very complicated process. Why would plants rely on one gene to keep from growing in the dark? But plants do.”

The discovery, published in the journal Cell in 1989, was eventually accepted, and it led to her lab unraveling the complete pathway of what happens at the molecular level when plants sense light, beginning with cell receptors.

"Just knocking out one gene caused that whole program to happen,” she said.

Chory has also done extensive work on the intense battle that occurs between adjacent plants fighting over light. Plants may appear passive in a field, she said, but a fierce competition for sunlight is taking place. Her lab determined the mechanism by which a shaded plant can outgrow its neighbor—important knowledge because dense planting leads to a major loss of yield.

In another study, described as a tour de force genetic study, Chory and her colleagues mapped the entire plant hormone signaling system, which controls a plant’s final size. They also found that more than 90 percent of the approximately 30,000 Arabidopsis genes reach peak expression at particular times of the day; this means their genes are most likely to trigger the creation of products, such as proteins, at certain times. What’s more, this timing changes with the seasons. 

The move into climate change work began in earnest in early 2017 with the Harnessing Plants Initiative, which Chory directs and speaks about around the world. The Salk Institute’s five plant biologists are combining efforts to seek ways to create “super plants”—plants that not only feed the world, but can also sequester carbon at higher rates than now possible. The team is looking for ways to grow more and deeper roots to keep carbon locked in the soil, rather than released into the atmosphere.

“This is going to be tricky,” Chory said, “because when you make more roots, you’re going to have less biomass aboveground, and sometimes you want that biomass—like with lettuce.”

They’re also looking at ways to increase levels of suberin, a compound mostly made in the roots. Suberin is the material that makes up cork and is very difficult for microbes to break down. If Chory and her colleagues can get more carbon to be stored in the form of suberin, it will be more stable and less likely to be degraded by microbes and released into the atmosphere.

However, too much suberin can create barriers that could prevent plants from drawing in enough nutrients. So the catch, Chory said, is to create enough suberin to exploit its benefits, such as storing carbon, without causing problems.

Their goal is to get plants to sequester 20 times more carbon in the form of suberin. If they can do that, and if those plants are used in 5 percent of the cropland in the world (roughly the size of Texas and New Mexico combined), farmers might be able to sequester half of the excess carbon dioxide that humans put into the atmosphere.

This is a much more economical and realistic way of extracting carbon dioxide from the atmosphere than the engineering solutions being explored, Chory said.

“If we go up another couple of degrees Celsius, the world is going to be a very different place,” she said of the climate change crisis. “This is a good time for biologists to step up.”

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Doug Peterson