Cornell Researchers Create a More Efficient Plant Using Genes from Cyanobacteria
For the first time, a genetically engineered plant is able to turn carbon dioxide from the atmosphere into sugars more efficiently...comments share
By Yvonne Huang via the Cornell Daily Sun, November 19, 2014
For the first time, a genetically engineered plant is able to turn carbon dioxide from the atmosphere into sugars more efficiently by using a bacterial enzyme.
Maureen Hanson, the Liberty Hyde Bailey professor of plant molecular biology, and Myat Lin, a postdoctoral fellow in Hanson’s lab, have successfully introduced a gene coding for a cyanobacteria protein into the chloroplasts of tobacco. By doing so, the transgenic plants are able to perform photosynthesis more efficiently.
“Rubisco is critical for carbon fixation in all plants,” Hanson said.
Photosynthesis is the series of reactions plants use to take light energy and convert it into chemical energy, or ‘food.’ The amount of an enzyme called Rubisco controls the speed of photosynthesis as a whole. Because of its importance in the photosynthetic cycle, Rubisco became the target of Hanson’s research, she said.
Because Rubisco evolved at a time when the Earth’s atmosphere was primarily carbon dioxide and had little to no oxygen, the modern-day enzyme is unable to differentiate between the two similarly-shaped molecules, according to Hanson. Rubisco will react with oxygen, but in order to successfully fix carbon for a plant, it must only react with carbon dioxide.
As the abundance of photosynthetic organisms increased and Earth’s atmospheric composition changed from having very little oxygen to being about one-fifth oxygen, photosynthetic organisms gradually had more trouble with Rubisco reacting with oxygen instead of carbon dioxide.
Most crop plants solve this problem by producing massive amounts of Rubisco, which ensures that at least some of its enzyme will end up reacting with carbon dioxide and helping produce sugars. However, because so much of the produced Rubisco is not actually fixing any carbon but rather reacting with oxygen, the photosynthetic process is considered very inefficient, according to Hanson.
Besides plants, other organisms like cyanobacteria are also able to carry out photosynthesis. Cyanobacteria, however, prevent their Rubisco from reacting with oxygen by enclosing it in a carbon concentrating mechanism, a micro-compartment called a carboxysome. The carboxysome prevents oxygen from entering and reacting with Rubisco while selectively allowing carbon dioxide to enter in order to carry out photosynthesis, according to Hanson. Because of the carboxysome, cyanobacteria are thought to be able to fix carbon much more efficiently, most notably into the form of glucose.
“This knowledge has been known for quite some time, but it is only in recent years that the technology available has made its application feasible,” Hanson said.
The three-year-old project was started in partnership with Rothamsted Research, a United Kingdom-based research group, after an Ideas Lab conference hosted by the National Science Foundation, Hanson said.
With concerns growing about crop productivity due to burgeoning global population, the NSF began searching for high risk, high reward projects to fund. Ideas Lab invites 15 scientists from the United States and 15 scientists from the United Kingdom to participate. Lin and Hanson’s project proposal was selected and they began the research in introducing genes for the carbon concentrating mechanism and Rubisco into plants.
Previous research by Lin, the Hanson lab and colleagues had introduced genes for carboxysomes into tobacco. The challenge was introducing the gene for cyanobacteria Rubisco.
“Assembly of Rubisco is very complex and is made of two unique subunits,” Lin said. “I put together the two genes that encode these two subunits of cyanobacteria Rubisco and introduced them into the tobacco genome.”
The transgenic plants were able to carry out photosynthesis and “supported autotrophic growth,” according to Lin. These tobacco plants subsequently were able to process more carbon dioxide per unit enzyme than their wild-type counterparts.
“We still have a few things to work out, such as regulating the cyanobacteria genes once they are introduced into the plant,” Lin said.
Once genes are introduced, their activity needs to be regulated in order for them to be considered fully functional, according to Lin.
The next step for Lin is to create plants that contain both the carboxysome genes and the Rubisco genes that were successfully introduced in this experiment.
“Of course, we don’t want to just do tobacco,” Hanson said. “Tobacco is a very good model system because of its convenience but eventually we would like to put this system into crop plants such as rice or wheat.”
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