Toxicity-Resistant Crops

Thursday, October 02, 2008

Researchers have engineered aluminum-tolerant crops.
By Mason Inman

(Note: If aluminum is common in soils, why is it just now necessary to develop aluminum-resistant crops? How did they grow before, with so much aluminum in the soil? Why is aluminum suddenly at such toxic levels?  Just a few questions that occur to me -- Ed.)


Aluminum foiled: When aluminum in soils gets activated by acidic conditions, it damages plants' DNA. In response, normal root cells stop in the middle of dividing (top row). But in plants with a mutation that makes them blind to the DNA damage, root cells keep dividing, bypassing aluminum's stunting effects (bottom row).
Credit: Megan Rounds and Paul Larsen, Current Biology publication date: Oct 2, 2008 (online) and October 14, 2008 (print)

Much of the world's cropland contains aluminum that stunts crops. But a new study has found a way to make plants grow tall in spite of the metal's toxic effects. The discovery, by plant biologists at the University of California, Riverside, suggests that genetic engineering could boost yields from fields that today are not ideal for growing crops.

Aluminum is common in soils--it's a major component of clay--but only in acidic soils does the metal form an ion that can dissolve into liquids and that's toxic to plants. Acidic soils make up as much as half the world's croplands, however, and aluminum toxicity is the main factor holding back crop growth in nearly 20 percent of the world's arable soils, including large areas of the United States east of the Mississippi River and northwestern Europe.

"The problem is, we have all these crop plants--wheat and corn and barley and so on--that didn't evolve or get developed on aluminum-toxic soils," study leader and professor of biochemistry Paul Larsen says. "They don't have natural resistance or tolerance to aluminum." Plant breeders are working on developing strains that can cope better with toxic aluminum, but they  have only been able to make incremental improvements, Larsen says.

In a study in Current Biology, Larsen and his colleague Megan Rounds have uncovered a simple mutation to a single gene that makes plants thrive in spite of levels of aluminum that would normally be toxic. Larsen and Rounds found the gene, called AtATR, by combing through mutants of Arabidopsis, a member of the mustard family that's commonly used in plant-genetics studies. The gene is related to a family of proteins known to help with finding and responding to DNA damage in nearly all multicellular organisms.

Toxic aluminum ions are known to damage DNA, and the new study suggests that plants respond by shutting down growth of cells in the tips of their roots when they accumulate too much DNA damage. Plants may have evolved this response to help them, over generations, cope with aluminum's toxic effects, Larsen speculates. But in the short run, it means that the plants are less healthy and are stunted and more vulnerable to stressors such as droughts.

From Article on Monsanto in the Atlantic Monthly:

….The Green Revolution can make Africa productive. The breakup of the former Soviet Union has caused its grain output to plummet, but if the new republics recover economically, they could produce vast amounts of food. More fertilizer can make the favored lands of Latin America -- especially Argentina and Brazil -- more productive. The cerrado region of Brazil, a very large area long assumed to be infertile because of toxic soluble aluminum in the soil, may become a breadbasket, because aluminum-resistant crop strains are being developed." This last is an example of agricultural advances and environmental protection going hand in hand…

From USDA Agricultural Research Service:

…Aluminum tolerance in wheat is regulated by the aluminum-tolerance gene ALTM1. When ALTM1 is activated, it triggers the release of malic acid, which bonds with the aluminum and neutralizes its toxic effect.

The research team found a gene in sorghum that protects the plant from soil aluminum via mechanisms that closely parallel ALTM1’s activity in wheat. In sorghum, the aluminum tolerance gene prompts the release of citric acid, which also binds to soil aluminum. But this sorghum transporter—dubbed SbMATEis not related to the ALMT1 transporter protein.

The team found that activity of SbMATE is activated in the roots of aluminum-tolerant sorghum only when aluminum is present in the soil. Under these conditions, SbMATE is most highly expressed in the first centimeter of the tip of the root. This optimizes the ability of the transporter to neutralize the aluminum and protect the sensitive root tip….