Photosynthesis uses the enzyme Rubisco and sunlight to turn carbon dioxide
and water into sugars essential for plant growth and yield. Over millennia,
Rubisco has created an oxygen-rich atmosphere, using oxygen instead of
carbon dioxide about 20 percent of the time, resulting in a plant-toxic
compound that must be recycled through the process of photorespiration.

"Photorespiration is anti-photosynthesis," said lead author Paul South, a
research molecular biologist with the Agricultural Research Service, who
works on the project Realizing Increased Photosynthetic Efficiency (RIPE) in
Illinois. "It costs the plant precious energy and resources that it could
have invested in photosynthesis to produce more growth and yield."

Photorespiration normally takes a complicated route through three
compartments in the plant cell. Scientists engineered alternate pathways to
reroute the process, drastically shortening the trip and saving enough
resources to boost plant growth by 40 percent. This is the first time that
an engineered photorespiration fix has been tested in real-world agronomic
conditions.

The researchers engineered three alternate routes to replace the circuitous
native pathway. To optimize the new routes, they designed genetic constructs
with different sets of promoters and genes, essentially creating a suite of
unique roadmaps. They stress tested these roadmaps in 1,700 plants to
identify the top performers. Over two years of replicated field studies, the
researchers found that these engineered plants developed faster, grew
taller, and produced about 40 percent more biomass, most of which was found
in 50-percent-larger stems. The team tested their hypotheses in tobacco and
is now translating their findings to boost the yield of soybean, cowpea,
rice, potato, tomato, and eggplant.

[www.igb.illinois.edu]
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