Could tinkering with photosynthesis prevent a global food crisis?
This story begins about two billion years ago, when the world, if not young, exactly, was a lot more impressionable. The planet spun faster, so the sun rose every twenty-one hours. The earliest continents were forming—Arctica, for instance, which persists as bits and pieces of Siberia. Most of the globe was given over to oceans, and the oceans teemed with microbes.
Some of these microbes—the group known as cyanobacteria—had mastered a peculiarly powerful form of alchemy. They lived off sunlight, which they converted into sugar. As a waste product, they gave off oxygen. Cyanobacteria were so plentiful, and so good at what they did, that they changed the world. They altered the oceans’ chemistry, and then the atmosphere’s. Formerly in short supply, oxygen became abundant. Anything that couldn’t tolerate it either died off or retreated to some dark, airless corner.
One day, another organism—a sort of proto-alga—devoured a cyanobacterium. Instead of being destroyed, as you might expect, the bacterium took up residence, like Jonah in the whale. This accommodation, unlikely as it was, sent life in a new direction. The secret to photosynthesis passed to the alga and all its heirs.
A billion years went by. The planet’s rotation slowed. The continents crashed together to form a supercontinent, Rodinia, then drifted apart again. The alga’s heirs diversified.
One side of the family stuck to the water. Another branch set out to colonize dry land. The first explorers stayed small and low to the ground. (These were probably related to liverworts.) Eventually, they were joined by the ancestors of today’s ferns and mosses. There was so much empty space—and hence available light—that plants, as one botanist has put it, found terrestrial life “irresistible.” They spread out their fronds and began to grow taller. The rise of plants made possible the rise of plant-eating animals. During the Carboniferous period, towering tree ferns and giant club mosses covered the earth, and insects with wingspans of more than two feet flitted through them.
Some two hundred million years later, in the early Cretaceous, plants with flowers appeared on the scene. They were so fabulously successful that they soon took over. (Charles Darwin was deeply troubled by the sudden appearance of flowering plants in the fossil record, describing it as an “abominable mystery.”) Later still, grasses and cacti evolved.
Through it all, plants continued to make a living more or less the same way they had since that ancient cyanobacterium took up with the alga. Photosynthesis remained remarkably stable over thousands of millennia of natural selection. It didn’t change when humans began to domesticate plants, ten thousand years ago, or, later, when they figured out how to irrigate, fertilize, and, finally, hybridize them. It always worked well enough to power the planet—that is, until now.
Stephen Long is a professor of plant biology and crop sciences at the University of Illinois Urbana-Champaign and the director of a project called Realizing Increased Photosynthetic Efficiency, or ripe. The premise of ripe is that, as remarkable as photosynthesis may be, it needs to do better.
At seventy-one, Long is thin and fit, with a craggy face and a voice so soft it borders on a murmur. He grew up in London in a working-class family and attended what he describes as “not the best” high school. (It’s since been closed.) One of the teachers at the school stood out—a plant enthusiast who took her students on frequent field trips. Inspired, Long decided to study agricultural botany at the University of Reading. Midway to his degree, he took a year off to work for a British food company, Tate & Lyle, which owned sugarcane plantations in the Caribbean and did a lot of sugar refining. Some at the company thought it might be possible to dispense with the plantations and even the cane and coax plant cells to produce sugar in vats. The idea didn’t pan out—“It never became economically feasible,” Long told me when, in July, I went to visit him at his office—but it got him interested in the mechanics of photosynthesis.
Photosynthesis takes place within a plant’s chloroplasts—tiny organelles that are the descendants of that original captured cyanobacterium. When a photon is absorbed by a chloroplast, it initiates a cascade of reactions that convert light into chemical energy. These reactions are mediated by proteins, which are encoded by genes. Through a second series of reactions, the chemical energy is used to build carbohydrates. This requires more proteins. Photosynthesis has been called “one of the most complex of all biological processes,” and when Long was starting out a great deal was still unknown about how, exactly, it worked. Gradually, using new molecular tools, researchers succeeded in filling in the gaps. Photosynthesis, they learned, requires the completion of some hundred and fifty discrete steps and involves roughly that number of genes…
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