4-01: Genetic dissection of bioenergy traits in sorghum

Sorghum 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 saccharification of the lignocellulosic biomass. The genetic basis of these traits, however, is poorly understood and impedes the full exploitation of sorghum as a bioenergy crop.  High throughput expression profiling using 454-sequencing is being applied to identify the gene(s) underlying a recently mapped quantitative trait locus (QTL) for stem sugar concentration. In addition, we are developing a population of recombinant inbred lines to map QTL for juice volume. To identify novel genes affecting cell wall composition, we are using a sorghum TILLING population to identify mutants, including bmr mutants, with improved saccharification properties. The Brown midrib genes from the most promising mutants are being cloned using a candidate-gene approach.  This approach recently resulted in the identification of Bmr6 as the gene encoding cinnamyl alcohol dehydrogenase2.  These combined approaches will enable the development of sorghums that offer maximum flexibility for the production of food, feed, fiber and fuel. Funding from the US Department of Energy for this project (DE-FG02-07ER64458) is gratefully acknowledged.