Scientists Decode a Plant’s Genome for First Time
After four years of effort, scientists from California and elsewhere have decoded the genome of a diminutive relative of cabbages and mustard, making it the first plant to have its genetic material fully described.
Researchers hope that understanding this “model plant,” Arabidopsis thaliana, will enable them to figure out better, “greener” ways to alter important crops--rendering them resistant to disease, for instance, or able to grow in warmer or colder climates.
“This will have equal significance--in terms of providing opportunities for improving human health and welfare--as sequencing the human genome,” said Steve Kay, an Arabidopsis researcher and a professor of cell biology at the Scripps Research Institute in La Jolla.
“It’s an incredibly exciting day,” said Virginia Walbot, professor of biological sciences at Stanford University, who wrote a commentary to accompany the paper, which is being published today in the British journal Nature.
Comparing the genomes of plants and animals--lineages that diverged from each other 1.6 billion years ago--is expected to reveal fascinating similarities and differences in how each evolved to cope with life on Earth.
And though Arabidopsis itself, commonly known as Thale cress, is worthless as a crop, the ease with which scientists can grow it and experiment with it makes it valuable for agriculture.
But reaping this genetic harvest will take a lot of work. Finding and describing all the genes is just one step. Now researchers have to figure out what all the genes do and how they act together to build and run a plant.
“Having the genome is a lot like having a glossary, a dictionary; it tells you all the words that exist,” Walbot said. “But you wouldn’t exactly predict Shakespeare’s sonnets from looking at a dictionary, even if all the words are present.”
The structure of the Arabidopsis genome was determined by a consortium of scientists in the U.S., Europe and Japan in a publicly funded effort known as the Arabidopsis Genome Initiative. Details of three of the plant’s five bundles of DNA, or chromosomes, were reported today; the structures of the other two chromosomes were reported a year ago.
Arabidopsis joins a growing list of life forms, including a fruit fly, a worm and sundry bacteria, viruses and fungi, whose genomes have been determined. A rough draft of the human genome was completed earlier this year.
Arabidopsis is perfect for research because it has a relatively small amount of DNA, breeds quickly and easily, produces masses of seeds and is so tiny you can grow the equivalent of a whole field’s worth on your windowsill, said Elliot Meyerowitz, head of the division of biology at Caltech and longtime advisor on the Arabidopsis genome effort.
“It’s kind of the ‘people’s plant.’ Anyone, anywhere can grow enough to do a good experiment,” he said.
Indeed, scientists around the world have used the weed to investigate everything from how and when a root, leaf or a flower is made to how a plant protects itself from salt, toxins, cold or sunlight.
Two repositories in the U.S. and U.K. house seed from thousands of different lines. Those include--among many others--tall and stunted plants, plants particularly susceptible or resistant to insects or molds and ones that make weird flowers consisting of nothing but female or male parts or just a cluster of leaves.
Already, those mutant plants have helped scientists track down genes that might help them breed better pest resistance in such crops as wheat or corn or get crops to flower at slightly different times of the year so they can grow in different parts of the world. The speed of such discoveries will only accelerate, now that the genome has been thoroughly described.
“You can take a gene for cold resistance, for example, from Arabidopsis and put it into a strain of wheat and confer resistance,” said Joseph R. Ecker, a professor at the Salk Institute for Biological Studies and one of the co-authors of the Arabidopsis genome effort.
Other California institutions with scientists involved in the effort include the USDA-UC Berkeley Plant Gene Expression Center in Albany, Calif.; the Stanford Genome Technology Center in Palo Alto; Stanford University Medical School; UC Davis; Caltech; and the Carnegie Institution in Stanford.
Tree-breeding, too, might become a more viable proposition. A few years ago, scientists inserted a certain Arabidopsis gene (called “leafy”) into an aspen tree and induced the seedlings to flower in just three months, instead of the normal 10 to 20 years.
Many of Arabidopsis’ 25,498 genes are related to each other, as if parts of the genome--instead of remaining quietly stable--have been copied repeatedly over the eons. Moreover, 139 Arabidopsis genes are similar to human disease genes. And there are hundreds of genes involved in sending signals from one part of the plant to another.
Now that the genome is in place, researchers can examine thousands of the plant’s genes at the same time to figure out when and where the genes are turned on and off--and thus how a plant grows and thrives.
Scripps’ Kay, for instance, used that approach to discover that Arabidopsis cleverly produces UV protectants before the sun comes up--and then turns on other genes that help protect it from cold before the sun goes down again. His findings will be published Friday in the journal Science.
“Plants,” he said, “put on sunscreen first thing in the morning, and they put on their bed socks at the end of the day.”
The little weed’s day in the sun has been a long time coming.
Arabidopsis thaliana was named for the 16th century botanist Johannes Thal, who discovered it growing in the Harz mountains in Germany. In 1943, another German biologist wrote that it would be a great model plant for geneticists to study.
“His paper was published in 1943, in Germany. You can imagine how much attention it got: None,” said Caltech’s Meyerowitz.
In 1975, geneticist George Redei of the University of Missouri also proposed that Arabidopsis would be just the ticket for geneticists. By that time, Redei had lost his research funding because he insisted on studying such a useless weed.
But his proposal began to take root--and came to full bloom in the 1980s.
Since the early ‘80s, Arabidopsis scientists have succumbed to occasional flashes of frivolity. Some have sent out Christmas cards with designs made from planting different -colored Arabidopsis plants in patterns. Others are considering marketing Arabidopsis plants that glow brightly in the dark--as better, brighter Chia pets.
