Map-Based Dissection of Sorghum Drought Tolerance Gene Networks

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Cereals provide seventy percent of the world's calories and water is the most limiting natural resource for grain production worldwide. Sorghum, a grass with its origin in Africa, is the fifth most important cereal worldwide. Sorghum has evolved characteristics that permit grain production in hot dry environments (i.e., thick leaf wax, deep root system) and that facilitate continued growth when water availability is limited. Sorghum is also similar in gene sequence to other important cereals such as rice, corn, and wheat and has a relatively small genome (only twice the size of rice and 20-fold smaller than wheat). Some sorghum genotypes show distinct drought-tolerance. Of particular interest are plants that continue to grow when experiencing water limitation, thus showing a 'stay-green' phenotype. A genomics approach will allow scientists to understand the network of genes that form the basis to stay green traits. To accomplish this, genomic resources will be further developed in Sorghum. The TAMU-ARS sorghum genetic and physical map, already established, will be further developed and will be aligned to the rice genome sequence. Sorghum chromosomes will be characterized and a virus-induced gene silencing system (VIGS/RNAi) will be established. Breeders are developing the genetic populations that permit precise chromosomal localization of drought tolerance genes, which is essential for candidate gene identification. All these genetic tools will be used to fine map, isolate, and characterize this network of genes that control expression of the sorghum stay-green trait that is central to grain production in water limited environments.Information will be made publicly available through scientific and popular publications, presentations at meetings, and through collaboration with the groups developing Gramene, a national relational database for grasses (http://www.gramene.org) and on a local project web site (http://SorghumGenome.tamu.edu). The complete sequence of several sorghum BACs, BAC sequence and other sequence data will be submitted to GenBank and DNA sequence data will be provided to the curators of Gramene. The information and technology generated will help public and private cereal breeders to improve US crop drought tolerance and productivity and will facilitate the transfer of the 'stay green' trait to other cereal species that lack sorghum's tolerance to drought.