Cornell researchers have cloned a novel aluminum-tolerant gene in sorghum and expect to have new genetically-engineered aluminum-tolerant sorghum lines by next year. This is a significant development considering there are extensive areas (see photo) that are highly acidic, with pH of 5 or below, particularly in the tropics or subtropics. The acidity of the soil dissolves aluminum normally immobilized in clay minerals, rendering the soil toxic and non-arable.

Kochian's research shows that in aluminum-tolerant sorghum varieties, special proteins in the root tip release citric acid into the soil in response to aluminum exposure. Citric acid binds aluminum ions very effectively, preventing the toxic metal from entering the roots.

Kochian and colleagues, including the paper's first author, Jurandir Magalhaes, who received his Ph.D. from Cornell in Kochian's lab and now directs his own lab at the Embrapa maize and Sorghum Research Center in Brazil, used genetic mapping to identify a single gene that encodes a novel membrane-transporter protein responsible for the citric acid release. The gene, they discovered, is only turned on to express the protein and transport citric acid when aluminum ions are present in the surrounding soil.

The researchers have now used the sorghum gene to engineer transgenic aluminum-tolerant Arabidopsis thaliana (a small mustard plant used in plant research because of its small genome and short life cycle) and wheat plants. Sorghum is harder to genetically transform, Kochian said.

The research will be published in the September issue of Nature Genetics.

Source: Cornell Chronicle Online