Scientists aim to feed the world by boosting photosynthesis

A little extra light goes a long way. By fixing a glitch in plants’ ability to use sunlight to make sugar, scientists have managed to improve the efficiency of photosynthesis by about 15% — an upgrade that could be used to raise agricultural crop yields.

The findings, described in the journal Science, could help researchers find ways to feed Earth’s ever-growing human population.

“That’s pretty amazing ... if this could be put into all of our food and feed and fuel crops, then it would solve certainly a decade or more’s worth of our need for these agricultural products,” said Sabeeha Merchant, a biochemist at UCLA who was not involved in the study.

Today’s grains and other crops look very different than the ones ancient humans first began to cultivate. Take the ancestor to modern corn, which featured tiny cobs with just a few kernels that were covered in tough shells. But several millennia of breeding, in which farmers selected for their preferred traits, resulted in the large cobs filled with hundreds of soft, sweet kernels — making it a much more calorie-dense and easily accessible food.

In more recent times, fertilizer has helped farmers pull far more produce from the earth; so have more sophisticated “molecular breeding” techniques, said Krishna Niyogi, a plant geneticist at UC Berkeley and Lawrence Berkeley National Laboratory and one of the paper’s senior authors. But there’s a limit to how far current technologies can take agriculture, he said.

“It’s thought that a lot of the gains of that initial breeding effort have kind of stalled and crop yields are not increasing fast enough at the moment to meet the projected demand for food by, for example, the middle of this century,” Niyogi said.

The human population is growing much faster than food is being grown: The United Nations’ Food and Agriculture Organization estimates that production will need to almost double in order to meet that demand — and so far, it’s not entirely clear how to do that.

So scientists have looked to new ways to get more bang for their agricultural buck — and one of the things they’re looking to do is improve photosynthesis, the process by which plants use sunlight to spin sugar out of water and air. Photosynthesis is surprisingly inefficient: Though the rate varies from plant to plant, many crops only utilize about 1% to 2% of of the light that hits a leaf’s surface.

For this paper, the researchers homed in on a strange glitch in the process. Plant leaves get damaged if they’re exposed to too much sunlight (metaphorically akin to the way your skin makes vitamin D under the sun but gets burned if you expose it for too long). To protect themselves from direct sunlight’s damaging effects, they use a mechanism called nonphotochemical quenching, which allows the plant to release some of that absorbed energy as heat — like a pressure-relief valve in a steam engine, Niyogi said.

This safety valve means the plant’s chloroplasts are operating at a lower efficiency in bright light, since they’re venting the energy as heat. So when the leaf moves back into the shade — whether because of a passing cloud, the motion of leaves above it, or the shadow of an animal — the plant needs to shut that valve and go back to using all of the available sunlight.

Niyogi and his colleagues realized that plants were taking too long to shut that safety valve once they were safely in the shade. And that delay could be costing plants a significant amount of sugar-making time.  

So the scientists decided to speed up the plants’ response times. They ramped up the production of three proteins involved in the nonphotochemical quenching process. They inserted the three relevant genes from Arabidopsis (a weed in the mustard family known as the “lab rat” of plant biology) into tobacco plants. They measured how much carbon dioxide the plants took in (to see how fast photosynthesis was occurring) and tallied up their total dry weight after they had grown.

The result: One of the tobacco plant lines was 14% more productive than unmodified plants, and two other plant lines consistently hit 20%.

Why doesn’t the plant already speed up this reaction time? It could simply be because plants originally didn’t evolve to be grown like crops, so closely packed together, with so many leaves overlapping.

“I think that might be part of the reasons why we’ve been able to improve on something that you’d think nature has been optimizing over a very long period of time,” Niyogi said.

Niyogi says his team is interested in trying these modifications out in crops like rice, though that may present a more complex challenge.

Merchant says more study is needed to see if the modifications result in any unforeseen consequences, but adds that the research could potentially have a global impact.

“I have my fingers crossed that they’ll put it into a crop plant and it’ll work,” Merchant said. “And even if it doesn’t work at 15%, even if it works at 5%, that’s still pretty good, if you think about how much agriculture we’re doing, not just in the U.S. but worldwide.”

amina.khan@latimes.com

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