Mary Lou Guerinot on Genetic Engineering and Plants

(Photo by Rob Strong ’04)


This Focus on Faculty Q&A is one in a ongoing series of interviews exploring what keeps Dartmouth professors busy inside—and outside—the classroom.

Molecular geneticist Mary Lou Guerinot, the Ronald and Deborah Harris Professor in the Sciences, spends a lot of time in the weeds—specifically, Arabidopsis thaliana, grown in a basement in the Life Sciences Center and notable as the first plant genome sequenced in 2000. Guerinot and her team of undergraduates, graduate students, and postdocs are working to improve the nutrient quality of this fast-growing model plant, with the goal of translating research to rice. In an interview at her office, Guerinot talks about what drives her professionally and what she’d like to say to the people with “No GMO” bumper stickers.

For 25 years, your work has focused mostly on a model plant rather than an actual food crop. What’s the big picture?

Over 3 billion people suffer from iron deficiency; it’s the No. 1 nutritional disorder in the world today. Most of those people are getting their iron from eating plants, so the idea is, because most people are eating rice, our ultimate target is to have the plants take up more iron as well as other essential nutrients, and then put those into the parts that people eat, but before we can do this in a crop, we want to prove the principle in a model plant.

Why don’t you just experiment on rice? Why work on a weed from the mustard family?

With rice you’re only going to get one crop a year, and it’s very difficult to grow in our greenhouse. Also, we do a lot of genetic engineering, so we’ll put a gene in and increase its expression and then see, for example, does that make the plant take up more iron? Those experiments are technically more difficult to do in soybeans or rice.

Has some of your work been applied to rice?

We haven’t done a lot of it ourselves, but we identified one gene that encodes a transporter, and we showed that it helps Arabidopsis plants store iron. Right now there’s a scientist carrying out those experiments at the International Rice Institute in the Philippines, where she has put the same gene into rice. That’s really exciting for us, because we may be able to see that something we did here is actually going to work to increase the iron content of food. Also, one of our genes has been put into cassava to increase its iron content, and cassava is a very important crop in Africa.

You were recently quoted in The New York Times in relation to another project you’re working on—decreasing the amount of arsenic in rice. Toxic rice? Really?

Depending on the geology, there can be two forms of arsenic in soil. So rice thinks it’s taking up phosphate (an essential nutrient), but the phosphate looks like arsenate so it takes arsenate up instead. Then, the other form of arsenic, arsenite, looks like silicate, and, in fact, rice is really good at taking up silicate. Rice uses silicate to strengthen its stems and to prevent insect damage. And so here it is thinking it’s taking up silicate, but if there’s arsenite, well then, it takes that up; in fact up to 10 times as much as other types of cereals. The arsenic ends up in the bran layer of the rice, which is retained in brown rice but which is polished off to make white rice, so brown rice actually has more arsenic than white rice.

Did the Times story cause a stir?

Yes, and so did research from our Superfund Research Group here at Dartmouth on organic brown rice syrup, which ends up in everything from power bars to infant formula. That got splashed all over ABC News and Dr. Oz. So now the pediatricians are saying you should always be feeding children a varied diet. You don’t have to start babies on rice cereal. And everything in moderation because this is a case where we really don’t have much data about what happens when you have chronic exposure to arsenic.

Do you still eat rice?

Yes, just not every day.

You majored in ecology at Cornell, then studied marine biology at Dalhousie University in Halifax, doing a diving project for your PhD. Can you talk about your career trajectory?

Remember the first Earth Day? I was going to be one of those people who were going to take care of the planet. I went to grad school and got involved in the story of why lobster populations were declining, and whether we were overfishing. I was working on sea urchins and did a postdoc in a marine microbiology lab, but then I switched to terrestrial systems for a second postdoc because my husband was going to go to graduate school and I was a little ahead of him professionally. It was right at the beginning of molecular genetics and the ability to identify and clone genes, move DNA around. So I sort of got into the field on the ground floor.

What appealed to you about molecular genetics?

It was going to open so many doors. We were going to be able to actually identify what genes were responsible for different traits.

Genetically modified foods. What exactly is the controversy?

I don’t know why people have fixated on this. We’ve been modifying plants for 10,000 years. A lot of plant breeding has been done sort of blindly, for example, selecting for celery that didn’t get eaten by insects. So they get celery that bugs don’t want to eat, but it turns out it has really high levels of a poisonous chemical called psoralen. But since the high-psoralen celery was bred naturally, they didn’t even have to test it.

With genetically modified foods, we argue that we’re manipulating plants, but it’s a different way of manipulating them. We know exactly what we’re putting in, often just one gene. Then the plants have to be tested like you wouldn’t believe before they can be released. People have been eating these products for over 20 years, and there are no data showing any adverse health effects.

So why the persistence of “No GMO” bumper stickers?

I think part of the reason people don’t like genetically modified foods is they’ve conflated it with agribusiness, and the idea that Monsanto controls everything. And of course it’s only the big companies that are bringing out these genetically modified crops. In fact, 94 percent of soybean is genetically modified in the states, and over 90 percent of the corn, and a lot of that ends up in all kinds of processed foods. If you ask, “What’s got genetically modified ingredients?” the answer is almost everything in the grocery store.

You’re involved with the American Society of Plant Biologists, and, until last year, served as chair of the board. What’s the incentive?

Well, because we have this issue with GMOs, and are trying to get the public on board, one of the ways is working with the society because it has a public affairs office. We don’t lobby, but we inform for science funding. So I’m doing my service for the larger scientific community.

You came to Dartmouth in ’85, and were originally hired as a microbiologist. Talk about the microbiology class you continue to teach to undergrads.

That’s a fun class. I teach it with colleagues from the microbiology and immunology department at the medical school. We give students a test tube with four to seven different bacteria mixed up together, and they have the rest of the term to isolate them and figure out what they are. They’re like detectives. Finally, we sequence the DNA from a bacterium they isolate from the environment, which is the really quick way to figure out what you have, but we’re trying to show them aspects of microbial metabolism as they identify their “unknowns.”

You and your husband, Rob McClung, also a plant molecular geneticist, have worked in the same department for 27 years. Is that nice, all that togetherness?

[Laughs] We’re used to it.



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