U.S. Savants Improve Crop Photosynthesis To Increase Yields

In order to feed a projected 9 billion people by 2050, farmers need to grow 50% more food on a limited amount of arable land. As a result, plant scientists are in a race against time to engineer crops with higher yields by improving photosynthesis, Phys.org reported.

Photo Insert: As the growing population demands an increased food supply, scientists race to innovate production.

Blue-green algae (cyanobacteria) are known to photosynthesize more efficiently than most crops, so researchers are working to put elements from cyanobacteria into crop plants. A new Cornell University-led study describes a significant step towards achieving that goal.

"Absence of Carbonic Anhydrase in Chloroplasts Affects C3 Plant Development but Not Photosynthesis," was published August 11 in the Proceedings of the National Academy of Sciences (PNAS).

WordsMaureen Hanson, professor of plant molecular biology, is the paper's senior author. Kevin Hines, a former student in Hanson's lab, and Vishal Chaudhari, a postdoctoral associate in Hanson's lab, are co-first authors.

When plants photosynthesize they convert carbon dioxide, water and light into oxygen and sucrose, a sugar used for energy and for building new tissues. During this process, Rubisco, an enzyme found in all plants, takes inorganic carbon from the air and "fixes" or converts it to an organic form the plant uses to build tissues.

One hurdle in improving photosynthesis in crops is that Rubisco reacts with both carbon dioxide and oxygen in the air; the latter reaction creates toxic byproducts, slows photosynthesis, and thereby lowers yields. But in cyanobacteria, the Rubisco is contained within microcompartments called carboxysomes that shield the Rubisco from oxygen.

The carboxysome additionally allows the cyanobacteria to concentrate carbon dioxide so Rubisco can use it for faster carbon fixation, Hanson said. "Crop plants don't have carboxysomes, so the idea is to eventually put in the entire carbon-concentrating mechanism from cyanobacteria into crop plants," she added.

To engineer this system to work in crop plants, scientists must remove carbonic anhydrase, a naturally occurring enzyme, from the chloroplasts, organelles in plant cells where photosynthesis occurs. That's because anhydrase's role is to create an equilibrium between CO2 and bicarbonate in plant cells, by catalyzing reactions in which CO2 and water form bicarbonate and vice versa.

But in order for the carbon-concentrating mechanism from cyanobacteria to work in crops, bicarbonate in the system must reach levels many times higher than those found at equilibrium. "So in this study," Hanson said, "we did that step [of removing anhydrase] that's going to be needed to make the carboxysome work."

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