Major breakthrough: researchers engineer sorghum that beats aluminum toxicity

In a development of major importance for world agriculture and the bioenergy sector, an international team of scientist has succeeded in cloning an aluminum-tolerance gene in sorghum, promising a boost to crop yields in vast parts of the developing world. Soghums are crops that can produce both food, feed and fuel. The new crops can be grown in the huge expanses of land plagued by aluminum toxicity. When soils are too acidic, aluminum that is locked up in clay minerals dissolves into the soil as toxic, electrically charged particles called ions, making it hard for most plants to grow. In fact, aluminum toxicity in acidic soils limits crop production in as much as 50% the world's arable land, mostly in developing countries in Africa, Asia and South America.

Acidic soils worldwide: aluminum toxicity in acidic soils limits crop production in as much as half the world's arable land

The scientists from Brazil's Embrapa, the US Plant Soil and Nutrition Laboratory (US Department of Agriculture's Agricultural Research Service), the Institute for Plant Genomics and Biotechnology (Texas A&M University), and the Department of Plant Pathology (Kansas State University) cloned a novel aluminum-tolerant gene in sorghum and expect to have new genetically-engineered aluminum-tolerant sorghum lines already by next year.

The research [*abstract], to be published in the September issue of Nature Genetics, provides insights into how specialized proteins in the root tips of some cultivars of sorghum and such related species as wheat and maize can boost aluminum tolerance in crops.

Sorghum is an important crop in Africa, Central America and South Asia and is the world's fifth most important cereal crop. Scientists also see the plant as a major energy crop and have received serious funding to develop drought-tolerant sorghums for biomass production (more here, here, here and here) as well as varieties that boost both food, fodder and fuel production all at the same time (earlier post, here and especially here). The new aluminum toxicity resistant plant could make sorghum a robust crop that can drive the bioeconomy forward.

My lab has been working to identify the physiological mechanisms of plant aluminum tolerance as well as its molecular basis. The reason this is significant is there are extensive areas of the earth's lands that are highly acidic, with pH of 5 or below [pH below 7 is considered acidic]. Most of these areas are in the tropics or subtropics, where many developing countries are located. - Leon Kochian, Cornell adjunct professor of plant biology and director of the U.S. Department of Agriculture -Agriculture Research Service (USDA-ARS) Plant, Soil and Nutrition Laboratory at Cornell; lead author

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:
energy :: sustainability :: ethanol :: biomass :: bioenergy :: biofuels :: :: agriculture :: energy crops :: sorghum :: aluminum toxicity :: soil :: developing world :: biotechnology ::

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 map-based cloning of this agronomically important gene in sorghum is helping advance this species as a model for further exploring the mechanisms of aluminum tolerance and discovering new molecular genetic solutions to improving crop yields, Kochian said.

"This research also has environmental implications for badly needed increases in food production on marginal soils in developing countries," said Kochian. "For example, if we can increase food production on existing lands, it could limit encroachment into other areas for agriculture." Alternatively, it could free up land for energy crop production.

The research is supported in part by the McKnight Foundation Collaborative Crop Research Program, the Generation Challenge Program, the National Science Foundation and the USDA-ARS.

Map: Aluminum toxicity in acidic soils limits crop production in as much as half the world's arable land, mostly in developing countries in Africa, Asia and South America. Credit: Cornell University Chronicle Online.

References:
Leon V. Kochian et. al., "A gene in the multidrug and toxic compound extrusion (MATE) family confers aluminum tolerance in sorghum", Nature Genetics, advanced online publication, 26 August 2007 | doi:10.1038/ng2074

Cornell University Chronicles Online: Cornell researchers clone aluminum-tolerance gene in sorghum, promising boost to crop yields in developing world - August 27, 2007

Biopact: ICRISAT harnesses ethanol from drought tolerant sweet sorghum - January 25, 2007

Biopact: Sun Grant Initiative funds 17 bioenergy research projects - August 20, 2007

Biopact: Joint Genome Institute announces 2008 genome sequencing targets with focus on bioenergy and carbon cycle - June 12, 2007

Biopact: ICRISAT's pro-poor biofuel projects provide livelihood and food security to landless farmers in India - August 13, 2007

Biopact: Researchers and producers optimistic about sweet sorghum as biofuel feedstock - July 27, 2007

Biopact: Mapping sorghum's genome to create robust biomass crops - June 24, 2007

Bipact: ICRISAT launches pro-poor biofuels initiative in drylands - March 15, 2007