Thanks to a genetic breakthrough, a large portion of Earth's now-inhospitable soil could be used to grow crops – potentially alleviating one of the most pressing problems facing the planet's rapidly growing population.

Scientists at the University of California, Riverside made plants tolerant of poisonous aluminum by tweaking a single gene. This may allow crops to thrive in the 40 to 50 percent of Earth's soils currently rendered toxic by the metal.

"Aluminum toxicity is a very limiting factor, especially in developing countries, in South America and Africa and Indonesia," said biochemist Paul Larsen. "It's not like these areas are devoid of plant life, but they're not crop plants. Among agriculturally important plants, there aren't mechanisms for aluminum tolerance."

The planet is rapidly running out of room to grow food, and scientists say that the world's booming population – expected to swell by half in the next 50 years – will outstrip food production. There's no more room for farms in the developed world; demand for cropland is fueling deforestation in the rain forests of Latin America and Africa; and the limits of the Green Revolution, which increased global food production through the use of pesticides and industrial farming techniques, have been reached. Another revolution, say agronomists, is needed.

In an effort to salvage currently infertile land, scientists have tried to understand the basic mechanisms of aluminum toxicity, and to find resistant food crops, but with little success. Larsen's research, published Thursday in Current Biology, could change that.

He identified a gene in Arabidopsis – a flower used as a model organism in basic plant research – that affects plants' sensitivity to aluminum. When the gene is modified, seedlings that would normally have died in aluminum-rich soils instead flourished.

There's no guarantee that the tweak will prove successful and safe – but if it does, it could provide food for millions.

Larsen and postdoctoral student Megan Rounds started with an especially aluminum-sensitive Arabidopsis strain, then used a DNA-scrambling mutagen to produce 200,000 seedlings with various mutations. When they scanned the genomes of a few that proved able to grow in aluminum-rich cultures, they found a common factor: a damaged gene called AlATR.

The gene appears to produce an enzyme that – when exposed to aluminum – stops cell division, preventing roots from growing.

"It was always believed that once aluminum got into the tissue" of a non-tolerant species, said Larsen, "it was 'game over' for the root.

It would accumulate toxic effects, and wouldn't grow. Here you change one gene, reduce the function of one protein, and all of a sudden you have a plant that can, for the most part, thrive in an aluminum-toxic environment. It was shocking."

"People have been studying aluminum toxicity for years. People say it binds to the cell wall. Others say it interacts with proteins. Others, that it damages the plasma membrane. Or that it screws up cytoplasmic calcium, or screws up the cytoskeleton, or binds the DNA, or mimics magnesium," said Leon Kochian, a Cornell University plant physiologist.

"This mechanism seems to supersede the others. It renders them immaterial."

Developing resistant plants may not be easy. Though defusing AlATR

protected the plants' roots, it made their leaves more sensitive to radiation. But Larsen suggests a workaround: Engineer plants that express the modified gene only in their roots, not their leaves.

If that works, the plants will still need to be proven safe. Such tampering is bound to raise concerns, but Larsen is hopeful that modifying the gene will have few other effects. He suspects the mechanism exists to prevent plants from accumulating aluminum-induced mutations, and passing them to future generations – protecting the genes of a population by sacrificing an individual. Most modern crops are replanted from year to year, so altering the mechanism wouldn't affect them.

Kochian said that genetic engineering may not even be necessary. In so-called smart breeding, farmers use genome sequencing to identify plants with the best AlATR alleles, then breed those to create resistant strains.

"You can do that with molecular tools, not biotechnology," said Kochian.

Larsen is currently trying to patent the technique, and said that he'll make it available to researchers in the developing world.

"I don't expect to make any money off it," he said. "I'd like it to trickle down to the people who need it.

He does worry that the technique could be used as an excuse to clear rain forests from currently aluminum-toxic soil. Instead of this, said

Larsen, already-cut land could be made more productive.

"If we can make use of the land that's available now, maybe we can make it so we don't have to cut forests down in the future," he said.

Aluminum-Dependent Root-Growth Inhibition in Arabidopsis Results from AtATR-Regulated Cell-Cycle Arrest [Current Biology]

Image: Root tips of the alt1-1 Arabidopsis strain display less damage in aluminum-rich solutions than non-resistant strains. Courtesy Current Biology*.*

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