Location: Wheat, Sorghum and Forage ResearchTitle: Genetic dissection of bioenergy traits in sorghum Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/15/2011
Publication Date: 4/11/2011
Citation: Vermerris, W., Saballos, A., Felderoff, T., Mitchell, S., Rooney, W., Murray, S., Kresovich, S., Pedersen, J.F., Sattler, S.E., Xin, Z. 2011. Genetic dissection of bioenergy traits in sorghum. Meeting Abstract presented at Genomic Science Contractor-Grantee Workshop/USDA-DOE Plant Feedstock Genomics for Bioenergy Awardee Meeting, April 10-13, 2011. Published online at https://www.orau.gov/gtl2011/abstracts/vermerris_wilfred.pdf. Interpretive Summary:
Technical Abstract: Sorghum is an attractive biomass crop for ethanol production because of its low water and fertilizer requirements, tolerance to heat and drought, and high biomass yield. Because of the species’ great genetic diversity (Murray et al. 2009), and the fact that sorghum is a diploid, seed-propagated crop, development of cultivars and hybrids adapted to a wide range of environments is feasible. Sweet sorghums are sorghums that can reach heights of up to 6 m and that accumulate soluble sugars in their stems. After squeezing the stalks, these sugars can be fermented directly and conveniently to ethanol or other biofuels. The crushed stems (bagasse) can then be processed as lignocellulosic biomass. Sweet sorghum thus represents an ideal bridge between sugar-based and cellulosic fuels, and, given the rapid establishment of sweet sorghum, this species is expected to be of particular value in extending the processing window of sugarcane-based biorefineries (Vermerris, 2011). In order to expand the area where sweet sorghum can be produced, both in terms of geographic location (daylength, temperature, pests and diseases) and local conditions (soil quality, water and nutrient availability), regionally adapted cultivars and hybrids need to be developed. The goals of this project are to gain better understanding of the genetic basis of both sugar accumulation and cell wall biosynthesis, in order to facilitate development of improved germplasm. Quantitative trait loci (QTL) associated with sugar concentration of the juice were identified in a recombinant inbred line population derived from the sweet sorghum ‘Rio’ and the grain sorghum BTx623 (Murray et al. 2008). A major QTL for sugar concentration is located on chromosome 3. We are employing high-throughput transcriptome profiling using the Solexa next-generation sequencing platform to identify the gene(s) underlying this QTL. This approach relies on comparing gene expression profiles of heterogeneous inbred families that are genetically highly similar except for the region containing the QTL. RNA was extracted from several different tissues and developmental stages and expression data are in the process of being analyzed. In addition, we have mapped QTL for juice volume, using a population of recombinant inbred lines derived from the dry-stem, non-sweet grain sorghum BTx3197 and the sweet sorghum ‘Rio’. Novel germplasm with an overall higher sugar yield can be developed by combining QTL (and ultimately loci) controlling juice volume and juice concentration. In order to improve the biomass-to-fuel conversion, we are focusing on brown midrib (bmr) mutants. The bmr mutations change the color and the chemical composition of the vascular tissue. Four independent loci were identified by Saballos et al. (2008) in a collection of mutants first described by Porter et al. (1978). Additional bmr mutants were identified in the TILLING population of Xin et al. (2008). Several bmr mutants from both populations have been shown to result in enhanced yields of fermentable sugars following enzymatic saccharification of sorghum biomass, even after thermochemical pretreatment (Saballos et al. 2008; Dien et al., 2009; Pedersen et al.; in preparation). As part of this project we have also cloned the Bmr6 and Bmr2 genes. The Bmr6 gene encodes the monolignol biosynthetic gene cinnamyl alcohol dehydrogenase (CAD) (Saballos et al. 2009; Sattler et al. 2009). The Bmr2 gene also encodes a cell wall biosynthetic enzyme (Saballos et al.; in preparation). Knowing the identity of the Bmr genes and the nature of the mutations in these genes has enabled the development of allele-specific markers that will allow more efficient use of these mutations in commercial breeding programs. Funding from the Office of Science (BER), U.S. Department of Energy grant DE-FG02¬07ER64458 is gratefully acknowledged.