For ancient plants, two genes were definitely better than one
By Deane Morrison
 |
| Researcher Nevin Young led a crack team of 124 scientists in deciphering an important piece of the genetic history of legumes. |
They doubled their genomes, and in that single act set the stage for feeding the world 60 million years later.
In a study published in the Nov. 16 issue of the journal Nature, researchers from the University of Minnesota and other institutions recount how sequencing the genome of a model, alfalfa-like legume revealed the monumental benefits that flowed when the ancestor of legumes acquired an extra copy of every gene.
The findings may help researchers genetically engineer legumes to do a better job of meeting the world's rising demand for nitrogen, the backbone of all protein and a major nutrient in fertilizers
Scientific symbiosis
The study was the result of a collaboration
among 124 co-authors at 31 institutions in
eight countries. Thelead gene sequencing
groups were at the University of Oklahoma
, the J. Craig Venter Institute, Genoscope
(France), and the WellcomeTrust Sanger
Institute. The other lead institutions:
the University of Minnesota, CNRS/INRA-
Toulouse (France), the John Innes Centre
(UK), the Noble Foundation, the University
of Wageningen (Netherlands), MIPS
(Munich), Ghent University (Belgium),
and the National Center for Genome
Resources.
Legumes supply nitrogen through a partnership (called symbiosis, Latin for "living together") with bacteria that live in the roots of the plants and turn inert nitrogen from the air into a biologically usable form. The process is called nitrogen fixation.
"Legume symbiosis with nitrogen-fixing bacteria is the largest source of natural, nonsynthetic nitrogen fertilizer in agriculture," says first author Nevin Young, a plant pathology professor at the University of Minnesota. "Understanding and leveraging symbiosis is the only possible way anybody can think of to expand the amount of natural fertilizer that gets into crops. The discovery [of genome duplication's role] is important in understanding how that symbiosis works."
To visualize that role, think of genes as jobs. Suppose one person is handling two jobs; he or she may well be mediocre at both. But if you could duplicate the person, you would get two people who could specialize and thus do each job better. That's what most plants, including the common ancestor of legumes, did with their genes nearly 60 million years ago.
How the genes doubled isn't known, but Young says it could have arisen from a mating where both "eggs" and "sperm" retained full-sized genomes.
Doubling the gene dose
Using the legume Medicago truncatula as the model, the researchers studied the fates of two genes in the ancestral plant, starting with the doubling of those (and all other) genes several million years after an asteroid struck Earth. That famous catastrophe occurred 65 million years ago, ending the Cretaceous Period and leading to the demise of the dinosaurs.
This simplified graphic shows how nitrogen-fixing bacteria in the roots of legumes perform the crucial first step in turning nitrogen in the air into nourishment for food plants and animals.
Both of the ancestral genes had performed dual functions. One was to help nitrogen-fixing bacteria infect the roots of the legume and enter into symbiosis with the plant. In this arrangement, the bacteria supply the plant with nitrogen so it can make protein, and in return, the plant supplies the bacteria with energy.
The ancestral genes' second function was to help the plant's roots interact with soil fungi that supply the plant with minerals, notably phosphorus, which the plant could not wrest from the soil by itself.
With the genome doubling, each ancestral gene now came in two copies. The researchers found that each copy evolved a different specialty: one involved with the plant's interactions with nitrogen-fixing bacteria, the other governing its relations with soil fungi. Both functions improved, and the ancestral legume evolved into many species, including top performers like soybeans, peas, beans, and peanuts, which supply most of the protein consumed by humans.
Cutting the fertilizer
Because of the similarity between the two plants, "everything we discover about Medicago is directly applicable to alfalfa," a major forage crop, Young says. The work will help scientists help legumes produce more nitrogen and phosphorus fertilizer.
"There are a lot of problems with fertilizers in water, and we spend a lot of money on synthetic fertilizer," says Young. "To keep agriculture sustainable, plants and people who grow plants will have to do a better job utilizing naturally occurring nutrients like nitrogen and phosphorus. [Besides legumes] the only way to make fertilizer is through mining or [fossil-fuel-intensive] factories.
"Plants can only do it with help from bacteria and fungi, and the discovery we made is important in understanding how that works."
Major U.S. funding for the research was provided by the National Science Foundation and the Noble Foundation.
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Twin Cities (U of M) is a public research university located in Minneapolis and St. Paul, Minnesota, United States. It is the oldest and largest part of the University of Minnesota system and has the four-largest main campus student body in the United States, with 52,557 students in 2011–2012. The university is considered a Public Ivy by Green's Guide.
Seal of the Regents of the University of Minnesota
Motto Commune vinculum omnibus artibus (Latin)
Motto in English A common bond for all the arts
Established 1851
Type Public Flagship University
Land-Grant
Sea-Grant
Space-Grant
Endowment US$2.224 billion in 2006 (systemwide)[1]
President Eric W. Kaler
Provost E. Thomas Sullivan
Academic staff 3,374[2]
Students 52,557[3]
Undergraduates 30,610
Postgraduates 17,187
Other students 4,760
Location Minneapolis and Saint Paul, Minnesota, USA
Coordinates: 44°58′31″N 93°14′03″W / 44.97528°N 93.23417°W / 44.97528; -93.23417
Campus Urban
2,730 acres (1,100 ha)
Colors Maroon & Gold
Athletics NCAA Division I
Big Ten Conference
Western Collegiate Hockey Association
Sports 24 Varsity Teams
Nickname Golden Gophers
Mascot Goldy Gopher
Affiliations Association of American Universities
Committee on Institutional Cooperation
Website umn.edu
Source: Wikipedia
