Functional Genomics of Sugar Content in Sweet Sorghum Stems

Enhancing the production and conversion of plant feedstocks to utilizable sources of energy will decrease the U.S. dependency on fossil fuels, while reducing greenhouse gas emissions. Sweet sorghum is a rapidly growing, high biomass, widely adaptable crop with tremendous potential for biofuel production. Sweet sorghum accumulates very high concentrations of sucrose in the stem, which can be efficiently converted to ethanol. We hypothesize that sucrose accumulation in sweet sorghum can be further improved if we understand the mechanisms regulating carbon allocation to stems. We are using a combination of approaches, spanning genomics, molecular genetics, biochemical phenotyping, and detailed physiological studies to identify bioenergy-relevant genes and to understand their functions in carbohydrate partitioning in sweet sorghum. Toward determining the mechanisms regulating the transport and partitioning of sucrose to sweet sorghum stem tissues, we are 1) mapping and characterizing quantitative trait loci (QTL) related to stem biomass, total biomass, and sugar accumulation in the stem in a population derived from a grain sorghum crossed by a sweet sorghum; 2) are determining the expression patterns and functions of a family of proteins, called sucrose transporters (SUTs), which are hypothesized to play essential roles in regulating carbon partitioning of sugar to sweet sorghum stems; and 3) are using detailed radiotracer (carbon-11) physiological and biochemical approaches to map and delineate the bottlenecks to sucrose allocation in sweet sorghum. From these data, we will generate a physiological knowledge base and determine which genes function in transport and allocation of assimilated carbon to stem tissues in sweet sorghum. The knowledge and germplasm generated by the project will make important contributions to advancing sweet sorghum for sustainable bioenergy production.