Web Exclusives: Genetics
Working Hand in Glove with Computational Biology
Think of a sunflower. You probably envision one large, heavy-headed flower on a stem. That's the domesticated kind (which, by the way, is the only major food crop that originated in North America). In the wild, there are dozens of other species, some of which grow in unusual and inhospitable places, like straight out of a sand dune or in the middle of a salt marsh.
Loren Rieseberg, an evolutionary biologist at the University of British Columbia in Canada, is an expert on these plants. He is studying them to learn how new species arise, how people can better control weeds, and whether we should worry about genetically modified organisms.
Using state-of-the-art techniques in genomics and computational biology, Rieseberg analyzes the genomes of five different sunflower plants (two common species and three extreme-habitat ones) to tease out the changes responsible for new traits. He then uses traditional greenhouse experiments to see if he's right.
He has learned that new species arise much more easily than was previously thought. With one hand on his keyboard and the other in a garden glove, he has shown that when two ordinary but dissimilar Midwestern sunflower plants mate, they occasionally produce hybrid offspring that can withstand extreme conditions. After about 60 generations, these hybrids have survival down to a science—and have evolved into new species like those below.
- Plants that thrive on sand dunes have very long tap roots to reach for water, and large, heavy seeds that roll on top of—rather than being blown off—the dunes.
- Marsh-dwelling sunflowers pump unwanted salt into cellular storage containers, grow slowly, and wait until the last possible minute to flower so that they can generate lots of seeds.
- Desert-dwelling plants, which have small, heat-tolerant leaves, grow quickly, flower early, and die before the dry season begins.
Rieseberg has honed in on the genes responsible for these adaptations. He can even replicate the development of the extreme species in his greenhouse within a few generations.
Hybridization—the genetic mixing of dissimilar parents—not only allows sunflowers to adapt to harsh conditions, it also creates some of the world's most noxious weeds. In addition to shedding light on how weeds become so annoyingly tenacious and invasive, Rieseberg's work also points to new ways to control plant pests.
Rieseberg, whose work initially focused the spread of natural plant traits, now also monitors the spread of transgenes—genes that are introduced by technology rather than by sexual reproduction. Yes, he says, the spread of such genes from genetically modified organisms into wild plants is inevitable. It's virtually impossible to prevent crops from interbreeding with wild and weedy neighbors. But whether these illicit unions cause ecological damage depends largely on whether the transgene helps plants survive in the wild.
The transgene bT, which enables plants to produce a bacterial protein that is toxic to caterpillars and beetles, is highly prized as a natural pesticide by organic farmers growing corn, cotton, or potatoes. Rieseberg and his colleagues discovered that the transgene gives sunflowers a huge survival advantage over their caterpillar-chomped neighbors. Fortunately, bT sunflowers are not available commercially. But if they are sold in the future, the bT gene is likely to spread rapidly in the wild, which could erode its value to farmers.
Another transgene lets plants resist a white mold that transforms plants into soft, slimy masses. While useful in many vegetable crops, the transgene wasn't all that helpful to sunflowers. So it would probably take a long time—more than 100,000 years, according to Rieseberg's computer models—to spread across wild sunflower populations.
In addition to its effect on plants, hybridization also helps create some of the world's most virulent viruses, including the notorious 1918 flu. A deadly virus—and a grisly crime—is grist for our next story.
You can learn more about Rieseberg's research at http://www3.botany.ubc.ca/rieseberglab/ .