It's one of the smallest and fastest-growing flowering plants that often becomes a hard-to-control weed in ponds and small lakes. But it's also been exploited to clean contaminated water and as a source to produce pharmaceuticals.
Duckweed is a relatively simple plant with fronds that float on the surface of the water and roots that extend into the water. In the flask on the left, you can see the dormant phase, turions, that have dropped to the bottom.
Credit: Wenquin Wang
Now, the genome of Greater Duckweed (Spirodela polyrhiza) has given this miniscule plant's potential as a biofuel source a big boost. In a paper published February 19, 2014 in the journal Nature Communications, researchers from Rutgers University, the Department of Energy Joint Genome Institute and several other facilities detailed the complete genome of S. polyrhiza and analyzed it in comparison to several other plants, including rice and tomatoes.
Simple and primitive, a duckweed plant consists of a single small kidney-shaped leaf about the size of a pencil-top eraser that floats on the surface of the water with a few thin roots underwater. It grows in almost all geographic areas, at nearly any altitude. Although it's a flowering plant, it only rarely forms small indistinct flowers on the underside of its floating leaves. Most of the time, it reproduces by budding off small leaves that are clones of the parent leaf. It often forms thick mats on the edges of ponds, quiet inlets of lakes and in marshes. It's among the fastest growing plants, able to double its population in a couple of days under ideal conditions.
These and other properties make it an ideal candidate as a biofuel feedstock – a raw source for biofuel production. For example, unlike plants on land, duckweeds don't need to hold themselves upright or transport water from distant roots to their leaves, so they're a relatively soft and pliable plant, containing tiny amounts of woody material such as lignin and cellulose. Removing these woody materials from feedstock has been a major challenge in biofuel production. Also, although they are small enough to grow in many environments, unlike biofuel-producing microbes, duckweed plants are large enough to harvest easily.
S. polyrhiza turns out to have one of the smallest known plant genomes, at about 158 million base pairs and fewer than 20,000 protein-encoding genes. That's 27 percent fewer than Arabidopsis thaliana – which, until recently, was believed to be the smallest plant genome – and nearly half as many as rice plants.
"The most surprising find was insight into the molecular basis for genes involved in maturation – a forever-young lifestyle," said senior author Joachim Messing, director of the Waksman Institute of Microbiology at Rutgers University.
S. polyrhiza leaves resemble cotyledons, embryonic leaves inside plant seeds that become the first leaves after germination. But where other plants develop other kinds of leaves as they mature, S. polyrhiza's never progresses and continuously produces cotyledon leaves. This prolonging of juvenile traits is called "neoteny." S. polyrhiza had fewer genes to promote and more genes to repress the switch from juvenile to mature growth.
"Because of the reduction in neoteny, there is an arrest in development and differentiation of organs. So this arrest allowed us to uncover regulatory networks that are required for differentiation and development," Messing said.
Also intriguing to the research team were which genes were preserved over time and which were not. Many of the genes responsible for cellulose and lignin production in land dwelling plants were missing, and there were fewer copies of those that were present. Genes for another compound related to cell walls called "expansins" which are involved with cell wall and root growth were also reduced.
Genes for starch production, on the other hand, were retained and are probably used for creating starch-filled turions, specialized buds produced by aquatic plants for overwintering, enabling them sink to the bottom of ponds and revive in warmer weather. Moreover, despite the reduced number of total genes, S. polyrhiza has more copies of genes for enzymes involved in nitrogen absorption and metabolism than in other plants. This is probably linked to the plant's ability to utilize excess nitrogen in contaminated waters.A thorough understanding of the genome and cellular mechanisms of S. polyrhiza could greatly enhance current efforts to recruit duckweed as a biofuel source. Messing estimates that duckweed will be a viable biofuel source within the next five years and points to Ceres Energy Group in New Jersey, which is already producing electricity from duckweed. Understanding which genes produce which traits will allow researchers to create new varieties of duckweed with enhanced biofuel traits, such as increased reduction of cellulose or increased starch or even higher lipid production. Starch can be directly used as a biofuel source and it can be converted to ethanol, the way corn is currently converted to ethanol fuel, but oils would have greater energy than ethanol.
This genome was sequenced as part of a DOE Office of Science JGI Community Science Program (CSP) project (formerly the Community Sequencing Program). It exemplifies the collaborative approach and innovative projects that the CSP enables among researchers. Messing pointed to the study's advances over previous research.
"The sequencing of this genome opens new frontiers in the molecular biology of aquatic plants," said Messing. "This publication represents the single largest advance in this field and a new milestone in plant molecular biology and evolution, as previous studies were either classical botany or biochemistry of photosynthesis. The placement of the Spirodela genome as a basal monocot species will serve as a new reference for all flowering plants."
The authors on the publication also include researchers from MIPS/IBIS, Helmholtz Center Munich, Germany; University of California, Davis; Georgia Institute of Technology; Brookhaven National Laboratory; Donald Danforth Plant Science Center; University of Jena, Germany, HudsonAlpha Institute for Biotechnology; and the Leibniz-Institute of Plant Genetics and Crop Plant Research (IPK), Germany.
The DOE Joint Genome Institute has announced a new call for letters of intent for the 2015 Community Science Program, due April 10, 2014. Details of the 2015 CSP call can be found at: http://bit.ly/CSP-15.
The U.S. Department of Energy Joint Genome Institute, supported by the DOE Office of Science, is committed to advancing genomics in support of DOE missions related to clean energy generation and environmental characterization and cleanup. DOE JGI, headquartered in Walnut Creek, Calif., provides integrated high-throughput sequencing and computational analysis that enable systems-based scientific approaches to these challenges. Follow @doe_jgi on Twitter.
DOE's Office of Science is the largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
David Gilbert | EurekAlert!
'Y' a protein unicorn might matter in glaucoma
23.10.2017 | Georgia Institute of Technology
Microfluidics probe 'cholesterol' of the oil industry
23.10.2017 | Rice University
Salmonellae are dangerous pathogens that enter the body via contaminated food and can cause severe infections. But these bacteria are also known to target...
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
23.10.2017 | Event News
17.10.2017 | Event News
10.10.2017 | Event News
23.10.2017 | Life Sciences
23.10.2017 | Physics and Astronomy
23.10.2017 | Health and Medicine