Researchers engineer plants for far higher photosynthesis efficiency
The research was aimed at speeding up the process of photosynthesis, whereby plants convert sunlight, water and carbon dioxide into oxygen and sugar.
Rubisco is the enzyme in plants responsible for fixing carbon into molecules that form the building blocks of plants, but it is considered to be extremely inefficient as it often reacts with oxygen instead of CO2 - one of the reasons why it is likely the most abundant protein on the planet.
What the scientists did was borrow a faster Rubisco enzyme from blue-green algae, or cyanobacterium, and put it into a tobacco plant.
Tobacco plants are considered to be a common model organism for genetic engineering research.
Teams led by Cornell University plant geneticist Maureen Hanson in the U.S. and Rothamsted Research plant physiologist Martin Parry in the U.K, worked in equal measure on the research, using Cornell's expertise in genetic engineering and Rothamsted's expertise in enzyme biochemistry.
The researchers transferred the cyanobacterium Rubisco into chloroplasts of the tobacco plant.
In some of the plants the researchers also added a bacterial protein that was thought to help Rubisco fold properly, while in others they added a bacterial protein that structurally supported Rubisco.
Both lines of tobacco were able to use the Rubisco for photosynthesis, and both reacted with carbon dioxide and created new molecules faster than normal tobacco.
Hanson explained that although this development was an important step for enhancing photosynthesis in crops, there was much work still to be done.
She added the newly engineered tobacco plant was 'not an improvement' over the natural plant as it did not have the oxygen-repelling bacterial microcompartments called carboxysomes needed for the GM plants to be of any use in natural conditions.
"The carboxysome normally encloses the enzyme, protects it from oxygen and increases the amount of carbon dioxide right around the enzyme so it can work faster," Hanson told www.freshfruitportal.com.
As the scientists were not able to use the carboxysomes, the genetically modified tobacco plants had to be grown in special chambers with a CO2 concentration 20 times higher than normal in order for photosynthesis to occur more quickly.
"If we were to include this carboxysome - which is what we're trying to do now - then the atmosphere right around the Rubisco enzyme would be very very high in CO2, and so photosynthesis could proceed more rapidly," she said.
"And that's why everyone's interested in doing this."
Hanson said another group led by Dr. Stephen Long at the University of Illinois had modeled a computer simulation of the potential effects on crop yield if photosynthesis efficiency were to be increased in this manner.
Their calculations indicated it could be anywhere from 36-60% higher.
"So that's why this is an exciting possibility, but we haven't finished the job - we have to get that carboxysome in there," she said.
The increase in yield is all the more important as many plant breeders are said to be reaching the end of their ability to use natural genetic variation to improve yields in some major global crops like rice and wheat
Hanson said it therefore looked like using modern genetic modification technology could be the best answer to the question of how to feed a rapidly growing world population.
GM technology 'absolutely necessary'
In order to make the carboxysomes in the genetically modified tobacco plants, a further 'six or seven' genes will need to be transferred into the tobacco plant chloroplast.
"That's what we're working on now - we're attempting to put all the genes in," Hanson said.
"It's a little bit trickier because you need to have not only the genes in there, but you have to have them controlled properly in order to make the right amount of protein."
Hanson said researchers might be able to put this mechanism into one major crop 'in a decade', but one of the main obstacles to it being adopted on a global scale would be people's reservations over GM technology.
"I'm hoping there will be increasing acceptance of genetically modified food as the people learn more about it and have some of the frankly unreasonable fears about it dispelled through education," she said.
"I don't see any way we can feed the world without using this technology. I think really it's absolutely going to be necessary, and when it becomes necessary then I think acceptance might increase."
Photo: Wikimedia Creative Commons