Researchers may have found the key to engineering plants capable of thriving in environments laden with toxic aluminum, according to a report published online on October 2nd in Current Biology, a Cell Press publication. Aluminum (Al)—a metal that is generally plentiful in the earth's crust—causes particular problems for farmers in South America, Africa, and Indonesia, where acidic environments turn the metal into a form that stunts the growth of plants and especially plant roots.
" We found that a single change in one plant factor required for monitoring of and response to DNA damage results in a profound increase in Al tolerance," said Paul Larsen of the University of California-Riverside.
That discovery was unexpected, he said, because scientists had believed Al could have a wide range of detrimental effects, binding to virtually any negatively charged molecule within cells. If that were true, getting around Al toxicity would be no easy task since any single change in plants would result in only incremental increases in Al tolerance.
" Surprisingly, we found that elimination of just one factor results in a mutant root that can now thrive in an Al toxic environment," Larsen said. The critical factor, known as AtATR, serves as a "checkpoint" for cell division, he explained. Its job is to assess whether a cell should divide or not, on the basis of the integrity of the cell's DNA. "Mutations that disrupt the function of AtATR effectively destroy this self-assessment activity and allow cells that otherwise would be forced to differentiate [into mature plant tissue] to continue dividing."
The results present a new view of the causes of Al toxicity. Rather than suffering from the metal's cumulative toxic effects as had been believed, it appears Al itself triggers the AtATR-controlled self-assessment pathway to shut down growth.
The findings made in the model plant Arabidopsis offer "readymade" tools for genetically engineering crop plants incapable of restricting root growth in response to Al toxicity, Larsen said. He anticipates that introduction of the mutant versions of AtATR into crop plants would override the existing assessment mechanisms and allow for continued cell division in soils that would normally inhibit root growth.
The new results may offer insight into Al toxicity not only in economically important agricultural crops, but also in animals, given that ATR genes are universally found in plants and animals, where they serve in various capacities related to DNA-damage assessment.
" To date, no one has been able to discern which targets of Al are critical to the manifestation of Al toxicity in either plant or animals, partly due to the predicted complexity of Al toxicity," he said. "This work clearly argues that DNA damage and response to this damage is paramount."
The researchers include Megan A. Rounds and Paul B. Larsen, of the University of California, Riverside, CA.