Using genomics approaches to improve crops for agriculture on marginal and degraded soils
CALS Impact Statement
The central theme of this work is the use of a systems biology approach integrating plant genomics, proteomics, molecular biology, molecular genetics, and plant physiology to better understand the molecular regulation of micronutrient metal transport and tolerance to toxic metals in soils. Specific objectives are: 1) to identify genes and associated mechanisms for aluminum tolerance in both cereal crops and Arabidopsis in order ultimately to enhance crop production on acid soils; 2) to elucidate the mechanisms underlying the extreme micronutrient (zinc) and heavy metal (cadmium) hyperaccumulation in Thlaspi caerulescens, in order to identify novel genes that can be used for the generation of plants better suited for the phytoremediation of metal-contaminated soils; and 3) to study the molecular regulation of micronutrient homeostasis in T. caerulescens and the related non-accumulator Arabidopsis thaliana in order to better understand how plants regulate the acquisition of essential yet potentially toxic micronutrients such as zinc and iron.
My research program uses an integrated molecular, genetic, and physiological approach to identify and characterize the mechanisms underlying toxic metal tolerance and transport in plants. The first component of the research deals with mechanisms plants use to tolerate toxic levels of aluminum that are found in acid soils and limit crop production in up to 50 percent of the land in the world. This involves the identification and characterization of genes and physiological mechanisms for aluminum tolerance in the important cereal crop species, maize and sorghum, with the long-term goal of improving crop production on acid soils. The second research component involves the extreme tolerance and accumulation of heavy metals exhibited by unique metal-hyperaccumulating plant species. The best known of the metal hyperaccumulators, Thlaspi caerulescens, can accumulate both the heavy metal cadmium and the essential micronutrient zinc in extremely high levels in the shoot. Research on this plant will provide the information and molecular tools that ultimately can be used to develop high biomass plants better suited for the phytoremediation of heavy metal-contaminated soils. Because our previous findings indicate that hyperaccumulation likely involves alterations in the processes plants use to acquire essential micronutrients, this research should also provide basic information on plant micronutrients that may be used to enhance the nutritional quality of food crops.
The first bona fide plant aluminum-tolerance gene was cloned in sorghum via map-based cloning approaches. This gene conditions the major sorghum aluminum tolerance locus, AltSB. AltSB encodes a novel membrane transporter that we have shown to mediate aluminum-activated citrate efflux from the sorghum root tip. AltSB is also the physiological mechanism of sorghum aluminum tolerance. The major difference in AltSB in tolerant versus sensitive genotypes is in expression and not function, in that it is expressed primarily in the root tip of only the aluminum-tolerant sorghum genotypes. We have now identified a number of different alleles of this gene, and have generated near isogenic lines harboring the AltSB introgression, in the same genetic background. This is allowing us to identify the best (alleles that confer the most acid soil tolerance) for breeding programs in Africa.
The discovery of this plant aluminum-tolerance gene opens up research aimed at elucidating the molecular mechanism of aluminum tolerance in plants and provides a tool for improving the acid soil tolerance of crop plants via both biotechnology and marker-assisted selection. This could have a significant impact on agriculture in developing countries in the tropics and subtropics, where acid soils are a primary limitation to food-crop production. A patent is pending regarding this discovery. Also, we are now beginning to work with sorghum breeders in Africa to identify the best alleles of our tolerance gene in their breeding germplasm. Also, we are identifying easy to generate markers for the best alleles and more acid tolerant sorghum lines will be generated for field testing in parts of Africa where acid soils predominate.
funding source description
Department of Agriculture
Funding from international agencies focusing on the resource poor in developing countries. This includes the McKnight Foundation and the Generation Challenge program.