Unit 6: Plant Form and Function: Joanne Chory
Interview: Joanne Chory

chory.jpgJoanne Chory is a professor of biology and Howard Hughes Medical Institute Investigator at The Salk Institute for Biological Studies in La Jolla, California. Her research has revealed key steps in the signal-transduction pathways by which light regulates the development of plants. Dr. Chory's dissection of such regulatory mechanisms also led to her discovery of the role of steroid hormones in this process and the identification of a plant steroid hormone receptor. In 1999, the central importance of Dr. Chory's research was recognized by her election to the National Academy of Sciences. As is often the case in biology, Dr. Chory's success has depended in part on selecting an appropriate organism as a research model—in this case, a tiny member of the mustard family named Arabidopsis, the "laboratory mouse" of modern plant biology. Plant science reached a milestone in 2000, when an international team announced the complete sequence of the Arabidopsis genome. The significance of that achievement seemed like a good place to start our interview with Dr. Chory.

Now that the Arabidopsis genome has been sequenced, how will this information affect plant biology?

First, it tells us how many genes it takes to be a plant. Arabidopsis has about 26,000 genes. We still don't know what most of those genes do, but now progress will be faster. It used to take two or three people several years to find and clone a gene. Now one graduate student can do this in just a few months.

How long do you think it will take to determine the functions of all the Arabidopsis genes?

There's a ten-year plan. About three years ago, the National Science Foundation could see that the sequencing of the rabidopsis genome was almost completed, so the next phase would be to figure out what all these genes do. So a committee of plant biologists developed a plan called The 2010 Project, which maps goals and strategies to determine the functions of all 26,000 Arabidopsis genes by the year 2010. This includes understanding at what time during the life cycle of the plant each gene is expressed and in which types of cells. Eventually, we'd like to have a "virtual plant." A researcher should be able to go to the computer and access the whole database of gene functions, with all the proteins produced in a particular part of the plant and at different times as the plant develops—a sort of four- dimensional map of the plant's gene expression during its life cycle.

How do you think researchers will use such a virtual plant?

Some people interpret the idea of a virtual plant to mean that we don't want to do experiments anymore. But that isn't true. What we want is to be able to design smarter experiments. The database of gene functions will help us formulate hypotheses for development of the plant—for example, how signaling networks interact in a specific cell at a specific time in development.

Why has so much effort focused on Arabidopsis, of all plants?

First, Arabidopsis has a very rapid life cycle. It takes only about seven weeks to go from seed to seed. Also, Arabidopsis is self-fertile, and each plant can produce 10,000 to 50,000 seeds, which means we can propagate a lot of genetically identical plants. Arabidopsis is also a good research plant because it has the smallest known plant genome. It doesn't have a lot of junk DNA. It would have taken much more time to sequence the genome of a crop plant, which may have 30 to 100 times more DNA than Arabidopsis. Although it's important to understand the biology of various crop plants, plant molecular biologists decided in the mid-1980s that it would be a lot more useful to pick a good research organism and try to understand it fully. And it has proven to be a wise decision to have a model or reference plant. Understanding Arabidopsis will help us understand flowering plants in general.

Are there any examples of how an understanding of Arabidopsis has had agricultural applications?

Yes. One example is what we've learned from Arabidopsis mutants about how the hormone ethylene functions in fruit ripening. The same genes responsible for the ethylene pathway in Arabidopsis are found in such fruits as tomatoes, and understanding how these genes work enables us to control the ripening process. Another application is that identifying genes in Arabidopsis can help breeders of crop plants understand how to use certain mutations in the process of selective breeding for useful varieties. For instance, sorghum would not normally grow in Texas, but breeders have selected for a mutation affecting a photoreceptor in the plant that we know, based on Arabidopsis research, would allow sorghum to complete its life cycle in Texas fields. So, this kind of connecting back and forth between a reference plant and crop plants has been really useful.

With the goal of improving human nutrition?

Yes, I think we need another green revolution because of the pace at which world population is growing. The predictions are for a population of 10 billion people in the year 2050. Even now, with 6 billion people, 800 million people suffer from chronic malnutrition. We have to figure out how to distribute food better, but that is more a question for governments than for plant biologists. For our part, I think the only way to improve nutrition in the world is to increase crop yields. This includes such crop traits as better resistance to pests. And I think crop improvement will depend on applications of molecular genetics, either to make breeding more effective or by producing genetically modified plants.

What about the concerns that many people have about genetically modified organisms in food?

I don't think there's a single response, because the objections to genetically modified crops are so diverse. For example, one whole group is critical because it just doesn't like the whole economic trend of globalization and worries that agricultural technology will make it possible for big multinational companies to control the food supply. And then there are the concerns about how safe it is for people to eat foods made from genetically modified organisms. But we've had genetically modified organisms in food for about 18 years already, and there are no data that indicate any danger. However, I think it's a good thing if these concerns result in government guidelines for assessing the safety of these products. Genetically modified crops will play a big role in the future, as long as people are confident that these products are safe and good for society. The farmers are completely on board about it, but the consumers need to see the benefits.

Much of your own research centers on how light regulates plants. Other than photosynthesis, how is light important in the life of a plant?

It's fascinating what plants can actually read from their light environment. Plants get such clues from light as what season it is and what time of day it is. For example, there's more red light compared to far-red light in the middle of the day, and a plant can tell this because it has a photoreceptor called phytochrome that can measure the ratio of red to far-red light. Light controls the development of plants in ways that optimize their performance as photosynthetic machines. So, if one plant is shaded by another, for example, it will elongate stems at the expense of expanding its leaves and grow toward light.

What mechanism do plants use to detect and respond to light?

There's an array of photoreceptors that function in different cell types throughout a plant's development. Once light is detected, these photoreceptors change their shapes and trigger signal pathways that affect transcription of specific genes in the nucleus.

How do you study these signal pathways?

We dissect the steps of a pathway by genetic analysis—by producing and identifying mutants that affect responses to light. So far, we've identified almost 50 mutant varieties of Arabidopsis that are affected abnormally by light. We know now that these signaling pathways are not linear sequences of events, but networks of interactions between proteins. It's going to be a big challenge to sort out these complicated webs of interactions, but I think it's worth it because, after all, responding to light is one of the most important things plants do.

You're also studying steroid hormones in plants. What are you learning?

Plant steroids, which are called brassinosteroids, do a lot of the same kinds of things as sex steroids do in humans. The more steroid a plant has, the bigger and tougher and more robust it is. When plants don't make a steroid—because of a mutation, for example—they are dwarfy things. Steroids also regulate sexual reproduction in plants. I think it's interesting how a certain group of molecules began functioning in diverse organisms as signaling molecules. Many of the enzymes a plant uses to make its steroids are also found in animals that make their own types of steroids. So some of the genes for these enzymes have probably been conserved since plants and animals diverged from a common ancestor over a billion years ago. However, the molecules of the signaling pathway for responses to steroids are very different in plants and animals.

How does plant research fit into the two institutions with which you're associated, the Salk Institute and the Howard Hughes Medical Institute?

Here at the Salk, there are only three plant scientists among the 57 faculty. And with Hughes, I think there are two plant scientists among 350 investigators. So in these organizations, plant scientists are still a little bit on the fringe. But I think there's an appreciation that it's important to study organisms that have different life strategies, which are of interest to all of us who study biology.

How did your interest in science and plants develop?

I was a late bloomer in science. I went to college at Oberlin not knowing what I wanted to major in, but I was good at science and math, so I kept these subjects in my curriculum. I took a biology course, and then genetics and microbiology courses. I did my Ph.D. in microbiology, but then became interested in plants for post-doctoral research. I was fascinated by how much we don't know about plants. In a way this makes it difficult to articulate a specific, sophisticated question or hypothesis. But that's also the fun of it. You get to work on really general questions that can lead you to discoveries.

Based on your personal experience, what advice do you have for undergraduates who are developing an interest in science?

I encourage an undergraduate who's interested in biology to seek an active researcher and volunteer to work on a project in the lab. There's nothing like the feeling of discovery, even if it's something really small. Although I liked science classes and lab courses, it wasn't until I did an honors thesis that I felt like I had my own little project. We have lots of undergraduates from UC San Diego doing honors projects in my lab here at Salk. The graduate students mentor the undergraduate students, and this is also a good experience for the grad students. The Salk Institute also has an outreach program for high school students to work in the lab during the summer. So my advice to students who are thinking of becoming scientists is to personalize science by actually doing it.

©2005 Pearson Education, Inc., publishing as Benjamin Cummings