Updated December 2008
INVESTIGATORS: W. Vermerris, S. Kresovich, S. Murray, J. Pedersen, W. Rooney, Z. Xin, and S. Sattler
INSTITUTIONS: University of Florida, Cornell University, Texas A&M University, and USDA-ARS
NON-TECHNICAL SUMMARY: Sorghum, a plant species related to corn and sugar cane, has a number of characteristics that make it a very attractive biomass crop for ethanol production: low water and fertilizer requirements, tolerance to heat and drought, high biomass yield, and great genetic diversity. Two traits of particular interest are the sweet sorghum trait, which results in the accumulation of fermentable sugars in the juice of the stems, and the brown midrib (bmr) trait, which changes the color and the chemical composition of the vascular tissue, and results in higher yields of fermentable sugars obtained after enzymatic processing of the lignocellulosic biomass. The genetic basis of these traits, however, is poorly understood and impedes the full exploitation of sorghum for bioenergy production.
OBJECTIVES: The objectives of this proposal are to 1) identify the gene(s) underlying a major quantitative trait locus (QTL) for stem sugar concentration identified in a prior study, 2) identify QTL for stem juice volume, 3) classify a population of novel sorghum bmr mutants in allelic groups based on cell wall chemistry and allelism tests, 4) select representative bmr mutants from each allelic group for their potential value as feedstock for ethanol production, and 5) clone novel Bmr genes.
APPROACH: Obj. 1 Tissue from plants of heterogeneous inbred families (HIFs) that are genetically similar but that have contrasting genotypes at a major QTL for stem sugar concentration will be used for high-throughput expression profiling to identify differentially expressed genes.
Obj. 2: We have generated a population of recombinant inbred lines (RILs) derived from crossing a juicy sweet sorghum with a dry-stalk, non-sweet sorghum. Juice volume and sugar concentration will be measured for each of the RILs and QTL for these traits will be identified based on genotypic data obtained using single nucleotide polymorphisms (SNPs).
Obj. 3 and 4: A large collection of novel bmr mutants was identified in a TILLING population developed by the USDA. These mutants will be classified based on allelism tests, their chemical composition will be determined, and representatives of each allelic group will be used to analyze biomass conversion efficiency.
Obj. 5: Comparisons between the chemical composition of the stems and leaves of brown midrib mutants and control plants will provide information on the role of each of the Brown midrib genes. By combining genetic mapping, current information on genes involved in cell wall biosynthesis, and the sorghum genome sequence, we will be able to identify the genes that are mutated in the brown midrib mutants.
Name: W. Vermerris