Building a Better Grain

Studying Carotenoids in Rice and Corn

Not all grains are created equal, as far as nutritional content goes. For instance, corn has something that rice lacks: betacarotene in its endosperm, or seed (the part that we eat). Betacarotene is converted to vitamin A, an essential nutrient for good health, in the human body. In areas where populations rely on rice as the major staple, particularly in Asia, the lack of vitamin A in the diet is a serious problem. Over 250 million children in developing countries are estimated to suffer from vitamin A deficiency, which can lead to blindness, increased mortality due to childhood diseases, and greater risk of transmission of viruses such as HIV. Professor Eleanore Wurtzel, who is on the faculty of The Graduate Center's Ph.D. Programs in Biology and Biochemistry and of Lehman College, is working to help solve this crisis by going to the source--she studies how betacarotene gets produced in the seeds of grains, and how plants can be enhanced to produce more of this important compound.

"I work on corn (or maize) and rice," says Wurtzel, taking some dried ears of corn from the bottom drawer of her office desk. The ears that she displays are a variety of colors, like you might see in a Thanksgiving decoration--yellow, white, orange, and red (and one a striped combination, the result of "unstable DNA"). The different colors, she explains, come from different types of carotenoids, the group of pigments that include betacarotene. There are over 600 chemical compounds of carontenoids, and a plant's ability to produce a particular one is traceable to its genes. The thrust of her research involves analyzing different genes and observing how they affect the biosynthetic pathways (the sequences of chemical reactions through which one type of biological material is converted to another) for carotenoids.

"If you have a better idea of how the genes are expressed, you can either manipulate the genes through using biotechnology tools, or you can use the molecular information for plant breeding," says Wurtzel, who is currently organizing an international conference on the topic, and has lectured on her work throughout Asia.

Wurtzel has been head of the Ph.D. Program in Biology's Plant Sciences concentration, which gains strength from its partnership with the New York Botanical Garden in the Bronx. Her research was funded for eight years by the Rockefeller Foundation's International Rice Biotechnology Program as well as the McNight Foundation and the American Cancer Society. "The idea was to see if we could produce the biosynthetic pathway [for carotenoids] in the seed...but the question was, 'Why doesn't rice have the capacity in the first place?'" she says. All plants produce betacarotene--it is needed for photosynthesis--but corn produces it in its seed, whereas rice does not. One of Wurtzel's goals is to understand not only how plants produce the pigment, but also how they manufacture it in their seeds.

In addition to her research on rice, she is currently funded by the National Institute of Health to study betacarotene production in corn (its levels are relatively low compared to those in, say, carrots or squash, and could be increased). She takes a multi-disciplinary approach to tackling the problem, involving the tools of classical genetics, molecular biology, and biochemistry.

"The idea is that you can take classical genetic tools-- observing plants as they grow, and the various genetic mutations--and then analyze the data in a different way in a molecular biology setting," she says.

Thus, the research takes place in two highly dissimilar environments that compliment one another well--a state-of-the-art molecular biology lab, employing the latest analytical machinery and computers; and a simple corn field of a few dozen rows, where Wurtzel can experiment with planting different genotypes and observing their characteristics, just as Gregor Mendel did with pea plants long before the discovery of DNA. "We grow the plants--we control the pollination of the mutants [or, different genetic variations]--and then we try to figure out what genes are missing," she says.

Studying rice (Oryza sativa) and corn (Zea mays), both known as "cereal grasses," side by side, allows Wurtzel to take advantage of information that is available about one grain and see if it can be applied to the other. "We're really going back and forth between maize and rice," she says. For instance, since the rice genome--its DNA with all its chromosomes, has essentially been sequenced, she is able to use this data to fill in gaps in knowledge about corn, and "If we've isolated the genes in corn, we can take those sequences and look for similar sequences in rice," she says. And corn has properties conducive to research that rice does not share; for instance, it is relatively easy to grow corn and to observe its genetic mutations just by looking at it. "We started out studying corn because as you learn in high school biology, it was the subject of classical genetics. There's a whole documented history, and many tools that you can use, dealing with corn. That's why we have a corn field."

The field is a new addition to the Lehman campus this year, since Wurtzel asked the administration to convert an unused patch of lawn beside the tennis courts into a garden. She uses irrigation systems and controlled pollination to study corn the old fashioned way: by growing it. "Each row is a different genotype," she says. There are mutants in this field which affect the biosynthetic pathway for carotenoids, but Wurtzel has to wait until the plants grow to see how the genes will be expressed.

Some mutations are visible, such as a row of stalks with oddly white-striped leaves that she excitedly points out, or another row that is not growing well. A plant may have a recessive gene, but there is no way of telling until it grows, she says, and different genes can be active at different points in the life cycle (the pigment may appear, for instance, when the plant is budding, or when it is dying). There is much to observe, and it is all information that will be analyzed in myriad ways--through color-separation analysis, DNA sequencing, and other advance techniques--in the lab.

"It's complex, but you can figure it out," she says. "You can do it by putting together different pieces of the genetic puzzle." When you think about it, it's well worth the effort and the wait: unlocking the secrets of these seeds to produce rice that grows yellow could one day help hundreds of millions live healthier lives.