Dec. 14, 2007 One of the simplest plants on the planet could help scientists create crops to survive the ravages of drought. The moss Physcomitrella patens is a primitive plant, similar to the first plants which began to grow on land around 450 million years ago. Just one cell thick, these early plants had to adapt to withstand cold, heat and drought without roots or complex leaves. The ability of mosses to survive severe dehydration and then regrow when watered could be of enormous use in crops grown in drought-stricken areas of the developing world.
Scientists from the University of Leeds, with colleagues from Germany, Japan and the USA, have sequenced the genome for Physcomitrella -- the first non-flowering or 'lower' plant to be sequenced -- and their findings are published in the December 14 issue of the journal Science.
Now that they have sequenced the moss's DNA, scientists will be able to identify which genes control these survival tactics and adapt crops to do the same.
"Physcomitrella is a really useful plant to study," explains Dr Cuming. "In addition to being the link between water-based algae and land plants, it also has many important characteristics which make it special. By sequencing the genome, we can start to identify their genetic basis and use the knowledge for crop improvement."
Physcomitrella has a single 'haploid' genome -- rather than a double genome from male and female parents -- which makes it easier to identify which characteristics link to which gene. The moss is also able to integrate new DNA into a defined target in the genome -- unlike most plants which integrate new DNA randomly. This means that modification of the moss genome is far more controlled than with other plants and allows the moss to be adapted as a 'green factory' to produce pharmaceutical products.
"If we can discover what mechanisms cause the Physcomitrella genome to integrate DNA in this way -- we may be able to transfer those to other plants, to allow more controlled modification of their genomes," said Dr Cuming. "However, we also believe many of the useful genes in Physcomitrella are probably still present in 'higher' crop plants, but are no longer active in the same way. So rather than adding new DNA -- we'll just be activating what's already there to create the properties we want."
"Physcomitrella is to flowering plants what the fruit fly is to humans; that is, in the same way that the fly and mouse have informed animal biology, the genome of this moss will advance our exploration of plant genes and their functions and utility," said Eddy Rubin, DOE JGI Director. "Traits such as those that allow plants to survive and thrive on dry land, will be useful in the selection and optimization of crops that may be domesticated for biomass-to-biofuels strategies."
Physcomitrella, with a genome of just under 500 million nucleotides and possessing nearly 36,000 genes (about 50% more than are thought to be in the human genome), is the first bryophyte to be sequenced. Bryophytes are nonvascular land plants that lack specialized tissues (phloem or xylem) for circulating fluids. Rather, they possess specialized tissues for internal transport. They neither flower nor produce seeds, but reproduce via spores.
"The availability of the Physcomitrella genome is expected to create important new opportunities for understanding the molecular mechanisms involved in plant cell wall synthesis and assembly," said Chris Somerville, Director of the Energy Biosciences Institute (EBI), the partnership between Lawrence Berkeley National Laboratory, U.C. Berkeley, the University of Illinois at Urbana-Champaign, and the global energy company BP. "The ease with which genes can be experimentally modified in Physcomitrella will facilitate a wide range of studies of the cell wall, the principal component of terrestrial biomass. Additionally, the moss has fewer cell types than higher plants and has a much more rapid lifecycle, which also greatly facilitates experimental studies of cell walls. Thus, the completion of the genome is an important step forward in facilitating basic research concerning the development of cellulosic biofuels."
"There is a clear connection with this work and the intensifying interest in the global carbon cycle," said Mishler, a U.C Berkeley Professor in the Department of Integrative Biology and Director of the University and Jepson Herbaria. "The moss system is proving quite useful for studies of photosynthesis among many other processes."
Quatrano said, "unlike vascular plant systems, we can target and delete specific moss genes to study their function in important crop processes, and replace them with genes from crop plants to allow us to study the evolution of gene function. In addition to the genome, extensive genomic tools are now available in Physcomitrella to study comparative gene function and evolution as related to bioenergy and other processes of importance to crops." These tools can be found at: www.mossgenome.org.
The sequencing has been carried out at the Joint Genome Institute in Berkeley, California, which invites scientists around the world to compete each year to use their sequencing facilities for a particular genome. Physcomitrella patens 'won' the competition in 2005. The work has been coordinated by the University of Leeds, the University of Freiburg in Germany, the National Institute for Basic Biology in Japan, Washington University at St Louis, Missouri and the University of California at Berkeley.
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