Genetically modifying photosynthesis


in Daily updates, Politics, Science, The environment

Dark path in Merton College

The European perspective on the genetic modification of foods generally seems like an unrelentingly negative one. While the dangers inherent to tinkering with nature are real and should be discussed, there are nonetheless a lot of appealing uses for the technology.

One significant example has to do with photosynthesis: the process whereby plants produce sugars from carbon dioxide and sunlight, generating oxygen as a by-product. Some plants use enzymes to turn CO2 into sugars composed of three carbon atoms (these are called C3 plants) while others have an enzyme (PEP Carboxylase) that allows them to produce four carbon sugars (C4 plants). The latter variety are much better at turning solar energy into sugars at temperatures above 25 degrees Celsius. The evolution of the C4 process has apparently taken place more than fifty times, in nineteen families of plant. Helping a few more important plants make the transition seems like it could be very beneficial.

C4 plants can be up to 50% more efficient than C3 ones in hot climates, while also using less water and nitrogen. Maize, a C4 plant, can yield a harvest of 12 tonnes per acre, while rice, a C3 plant, does no better than eight. If we could genetically modify rice to be a G4 plant, we could simultaneously increase crop yields, reduce the water and fertilizer needs of farmers in hot areas, and produce crops that would be less vulnerable to global warming. While there could certainly be some nasty unintended consequence of doing so, that does not seem like sufficient cause not to try.

The idea that the foods we eat now are ‘natural’ is not one that meshes very well with the fact that they have been ceaselessly modified, over thousands of years, through selective breeding. While there may be special dangers involved in mixing genes in the lab rather than out in the fields, there are also special opportunities, like the one listed above. It will be interesting to see if someone manages to pull it off.

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{ 9 comments… read them below or add one }

R.K. January 21, 2007 at 3:13 pm

Another useful rice modification:

Waterproof rice can outlast the floods

“Rice grows best in flooded paddy fields. Too much water, however, and modern high-yield varieties drown within a few days. The downside of having bumper crops in good years is that the crops are vulnerable to the kind of floods that regularly trouble south and south-east Asia. More than $1 billion of rice is lost this way every year.

Now researchers have tracked down a gene in an old variety of rice largely abandoned by farmers that allows the plant to survive complete submersion. They say it could be the first lost gene of a series to be introduced into modern rice varieties to make rice more resilient to environmental hazards.”

Milan January 25, 2007 at 12:19 am

A talk on this, for any interested Oxonians:

“Using C3 species to provide insight into the evolution of C4 photosynthesis”
Dr Julian Hibberd – University of Cambridge
Thurs 25th, 4pm, Large Lecture Theatre, Plant Sciences
Organiser: Plant Sciences

. August 11, 2008 at 11:44 am

GM companies also aren’t being honest about what this technology can do—and what it can’t. In the rush to exploit the current crisis, the industry routinely promises to re-engineer crops to give massive yields—Monsanto has vowed to double grain yields by 2030—or to grow with less water or to thrive in degraded soils. But delivering on such promises will be much harder than is currently acknowledged. Whereas making corn tolerate Roundup required the manipulation of just one gene, boosting yield is vastly more complex, says Kendall Lamkey, a crop-breeding expert who chairs Iowa State University’s Department of Agronomy. Yield is the expression of a plant’s reproductive success, and reproduction takes nearly all of a plant’s survival “skills,” from its capacity to cope with temperature changes to its resistance to bugs. In other words, says Lamkey, to boost yields through genetic modification, GM companies must manipulate thousands of genes—and so far, they’ve had limited success.

. November 14, 2008 at 5:26 pm

Crassulacean acid metabolism, also known as CAM photosynthesis, is an elaborate carbon fixation pathway in some plants. These plants fix carbon dioxide (CO2) during the night, storing it as the four carbon acid malate. The CO2 is released during the day, where it is concentrated around the enzyme RuBisCO, increasing the efficiency of photosynthesis. The CAM pathway allows stomata to remain shut during the day; therefore it is especially common in plants adapted to arid conditions.

The C4 pathway bears resemblance to CAM; both act to concentrate CO2 around RuBisCO, thereby increasing usefulness. CAM concentrates it in time, providing CO2 during the day, and not at night, when respiration is the dominant reaction. C4 plants, on the contrary, concentrate CO2 spatially, with a RuBisCO reaction centre in a “bundle sheath cell” being inundated with CO2.

. December 1, 2008 at 10:30 am

Of rice and men
Perennial rice on the rise?
Posted by Erik Hoffner

“It was good to read this weekend in the Land Institute’s The Land Report that they’re now working hard to develop perennial rice varieties (in addition to their well-known perennial prairie polyculture experiment, which could transform large parts of the American plains back into a wildscape that produces lots of food).

Because agriculture is technically the world’s largest ecosystem, moving it toward a perennially-cropped system will have major impacts on soil health/soil building, biodiversity, energy use, and possibly carbon sequestration. “

. March 24, 2009 at 5:22 pm

My Ada Lovelace day post: Constance Hartt
March 24, 2009, 7:05 am

Hartt was a laboratory researcher at the Hawaiian Sugar Planters Association Experiment Station, and her assiduous work on the biochemistry of sugar cane in the 1930s and 1940s convinced her that, for that plant at least, the primary product of photosynthesis is malate, a four carbon sugar. Later carbon-14 studies showed that she was right — and led to an interesting conundrum. Why did some plants — most plants, indeed, and almost all algae — make a three carbon sugar, phophoglycerate, while sugar cane and, it later became clear, various other grasses made a four-carbon sugar?

The answer lies in the process of photorespiration. The enzyme which fixes carbon into phosophglycerate, rubisco, is very ancient and rather easily confused — left to itself it will sometimes grab oxygen molecules rather than carbon dioxide molecules, and instead of making phosphoglycerate makes phosphoglycolate.

. April 15, 2009 at 1:29 pm

Genetic engineering isn’t increasing crop production or resistance to climate change — report (04/15/2009)

Lea Radick, E&E reporter

A new report from the Union of Concerned Scientists asserts that biotechnology has not increased crop yields, nor has it improved crop resistance to the negative effects of climate change.

Instead, the nonprofit organization found that any increases in crop yields over the last decade can instead be attributed to conventional breeding practices, such as organic and low-external-input methods.

These methods are used to reduce the amounts of fertilizer and pesticides — both contributors to greenhouse gas emissions — that go into typical industrial crop production.

Brian Cady September 3, 2012 at 1:36 pm

Alexandra Maier et al have altered a C3 plant to photosynthesize mor efficiently, with some success, documented in a 2012 paper here:

. July 15, 2016 at 8:01 pm

C4 SOUNDS like the name of a failed electric car from the 1970s. In fact, it is one of the most crucial concepts in plant molecular biology. Plants have inherited their photosynthetic abilities from bacteria that took up symbiotic residence in the cells of their ancestors about a billion years ago. Those bacteria’s descendants, called chloroplasts, sit inside cells absorbing sunlight and using its energy to split water into hydrogen and oxygen. The hydrogen then combines with carbon dioxide to form small intermediate molecules, which are subsequently assembled into sugars. This form of photosynthesis is known as C3, because these intermediates contain three carbon atoms. Since the arrival of chloroplasts, though, evolution has discovered another way to photosynthesise, using a four-carbon intermediate. C4 photosynthesis is often more efficient than the C3 sort, especially in tropical climes. Several important crops that started in the tropics use it, notably maize, millet, sorghum and sugar cane.

C4 photosynthesis is so useful that it has evolved on at least 60 separate occasions. Unfortunately, none of these involved the ancestors of rice, the second most important crop on Earth, after wheat. Yet rice, pre-eminently a tropical plant, would produce yields around 50% bigger than at present if it took the C4 route. At the International Rice Research Institute in Los Banos, outside Manila, researchers are trying to show it how.

The C4 Rice Project, co-ordinated by Paul Quick, is a global endeavour, also involving biologists at 18 other laboratories in Asia, Australia, Europe and North America. Their task involves adding five alien enzymes to rice, to give it an extra biochemical pathway, and then reorganising some of the cells in the plant’s leaves to create special compartments in which carbon dioxide can be concentrated in ways the standard C3 mechanism does not require. Both of these things have frequently happened naturally in other plants, which suggests that doing them artificially is not out of the question. The team has already created strains of rice which contain genes plucked from maize plants for the extra enzymes, and are now tweaking them to improve their efficacy. The harder part, which may take another decade, will be finding out what genetic changes are needed to bring about the compartmentalisation.

The C4 Rice Project thus aims to break through the yield plateaus and return the world to the sort of growth rates seen in the heady days of the Green Revolution. Other groups, similarly motivated, are working on making many types of crops resistant to drought, heat, cold and salt; on inducing greater immunity to infection and infestation; on improving nutritional value; on making more efficient use of resources such as water and phosphorous; and even on giving to plants that do not have it the ability to fix nitrogen, an essential ingredient of proteins, directly from the air instead of absorbing it in the form of nitrates. Such innovations should be a bonanza. Unfortunately, for reasons both technical and social, they have so far not been. But that should soon change.

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