Photosynthesis hack needed to feed the world by 2050

March 27, 2015

Pipeline of transformation of leaf discs of tobacco (easily transformed and forms a closed canopy) with constructs for improved photosynthetic efficiency through regeneration on selective media, growth of the initial transformants to seed, and then testing of transgenes in replicated field plots (credit: Stephen P. Long et al./Cell)

High-performance computing and genetic engineering could boost crop photosynthetic efficiency enough to feed a planet expected to have 9.5 billion people on it by 2050, researchers report in an open-access paper in the journal Cell.

“We now know every step in the processes that drive photosynthesis in plants such as soybeans and maize,” said University of Illinois plant biology professor Stephen P. Long, who wrote the report with colleagues from Illinois and the CAS-MPG Partner Institute of Computational Biology in Shanghai.

Improvement strategies

“We have unprecedented computational resources that allow us to model every stage of photosynthesis and determine where the bottlenecks are, and advances in genetic engineering will help us augment or circumvent those steps that impede efficiency. Long suggested several strategies.

Add pigments. “Our lab and others have put a gene from cyanobacteria into crop plants and found that it boosts the photosynthetic rate by 30 percent. ” But Long says we could improve that. “Some bacteria and algae contain pigments that utilize more of the solar spectrum than plant pigments do. If added to plants, those pigments could bolster the plants’ access to solar energy.

Add the blue-green algae system. Some scientists are trying to engineer C4 photosynthesis in C3 plants, but this means altering plant anatomy, changing the expression of many genes and inserting new genes from C4 plants, Long said.

“Another, possibly simpler approach is to add to the C3 chloroplast the system used by blue-green algae,” he said. This would increase the activity of Rubisco, an enzyme that catalyzes a vital step of the conversion of atmospheric carbon dioxide into plant biomass. Computer models suggest adding this system would increase photosynthesis as much as 60 percent, according to Long.

More sunlight for lower leaves. Computer analyses of the way plant leaves intercept sunlight have revealed other ways to improve photosynthesis. Many plants intercept too much light in their topmost leaves and too little in lower leaves; this probably allows them to outcompete their neighbors, but in a farmer’s field such competition is counterproductive, Long said. Studies headed by U. of I. plant biology professor Donald Ort aim to make plants’ upper leaves lighter, allowing more sunlight to penetrate to the light-starved lower leaves.

Eliminate traffic jams. “The computer model predicts that by altering this system by up-regulating some genes and down-regulating others, a 60 percent improvement could be achieved without any additional resource — so 60 percent more carbon could be assimilated for no more nitrogen,” Long said.

In silico simulation. “The next step is to create an in silico plant to virtually simulate the amazingly complex interactions among biological scales,” said U. of I. plant biology professor Amy Marshall-Colon, a co-author on the report. “This type of model is essential to fill current gaps in knowledge and better direct our engineering efforts.”

30 years lead time

The work should be undertaken now, Long said. “If we have a success today, it won’t appear in farmers’ fields for 15 years at the very earliest,” he said. “We have to be doing today what we may need in 30 years.”

Stephen Long is a professor in the Carl R. Woese Institute for Genomic Biology at Illinois, and also has an appointment in the department of crop sciences.

Funding for this work was provided by the Bill & Melinda Gates Foundation, the U.S. Department of Agriculture, the National Science Foundation, and the Chinese Academy of Sciences.

Abstract of Meeting the Global Food Demand of the Future by Engineering Crop Photosynthesis and Yield Potential

Increase in demand for our primary foodstuffs is outstripping increase in yields, an expanding gap that indicates large potential food shortages by mid-century. This comes at a time when yield improvements are slowing or stagnating as the approaches of the Green Revolution reach their biological limits. Photosynthesis, which has been improved little in crops and falls far short of its biological limit, emerges as the key remaining route to increase the genetic yield potential of our major crops. Thus, there is a timely need to accelerate our understanding of the photosynthetic process in crops to allow informed and guided improvements via in-silico-assisted genetic engineering. Potential and emerging approaches to improving crop photosynthetic efficiency are discussed, and the new tools needed to realize these changes are presented.