Modified genes in photosynthesis boosts crop yield

Researchers have increased the production of specific genes to make use of light more efficient by tobacco, effectively boosting the productivity of the model crop.

The research results from plant biologists at the U.S. Department of Energy's Lawrence Berkeley National Laboratory, the University of California, Berkeley, and the University of Illinois were described in the latest issue of the journal Science.

By targeting three genes involved in a process plants use to protect themselves from damage when they get more light than they can safely use, they increased the expression of those genes, and saw increases of 14-20 percent in the productivity of modified tobacco plants in field experiments.

In photosynthesis, plants use the energy in sunlight to take up carbon dioxide from the atmosphere and convert it into biomass, which is used for food, fuel and fiber. When there is too much sunlight, the photosynthetic machinery in chloroplasts can be damaged, so plants need photoprotection. Inside chloroplasts, plants have a system called NPQ, or nonphotochemical quenching, for this purpose.

Study co-senior author Krishna Niyogi, a UC Berkeley professor of plant and microbial biology, compared NPQ to a pressure relief valve in a steam engine. "When there is too much sunlight, it's like pressure building up. NPQ turns on and gets rid of the excess energy safely. In the shade, the pressure in the engine decreases. NPQ turns off, but not quickly enough. It's like having a leak in the system with the valve left open."

Noting that the photosynthetic engine can't work as efficiently, the researchers deem the highly variable levels of light plants receive, particularly in densely planted crop fields, as a challenge to the efficient use of solar energy.

To help plants adapt to intermittent shading from leaves that are higher in the canopy, or from passing clouds, Niyogi and his colleagues figured out a way to speed up recovery from photoprotection and demonstrated a proof of this concept in the laboratory. By boosting the expression of three genes involved in NPQ, they showed that NPQ turned off more quickly, and the efficiency of photosynthesis in the shade was higher.

The trio of genes then were put into tobacco plants for further testing in greenhouse and field experiments.

As half of crop photosynthesis occurs in the shade, the researchers said, any improvement in speeding up recovery from photoprotection could have a big benefit.

"Tobacco was used as the model crop plant in this study because it is easy to work with, but we're working to make the same modifications in rice and other food crops," Niyogi was quoted as saying in a news release. "The molecular processes we're modifying are fundamental to plants that carry out photosynthesis, so we hope to see a similar increase in yield in other crops." Endit