Large-scale cultivation of bioenergy crops on low-productivity land and with minimal inputs of fertilizer and chemicals can contribute to the sustainable production of fuels and chemicals as alternatives to petroleum-derived products. This requires, however, fundamentally different crop improvement strategies than the ones that have been implemented to maximize the yield of commodity crops since the Green Revolution.
Sorghum (Sorghum bicolor (L.) Moench), a diploid grass that originated in Africa, is a promising bioenergy crop due to its great yield potential with low input requirements. It is also tolerant to a wide range of growing conditions, due to its great genetic diversity. The availability of the sorghum genome sequence has facilitated genetics and genomics studies.
Genetic improvement of sorghum as a feedstock for renewable fuels and chemicals will benefit greatly from the elucidation of a number of quantitative traits: 1) Disease resistance: Successful expansion of the crop on low-productivity land, especially in the southeastern United States, depends on resistance against the most prevalent diseases, including anthracnose, a fungal disease that can result in yield losses of up to 70%. Several sources of anthracnose resistance have been identified and we recently fine-mapped two novel, major anthracnose QTL and are currently validating a small number of candidate genes using virus-induced gene silencing. 2) Flooding tolerance: Production of bioenergy crops on land that is prone to seasonal flooding minimizes competition with food production, but requires plants able to withstand water logging. We have identified a number of sorghum genotypes that can tolerate prolonged flooding by forming aerial roots that float on the water. High-throughput expression profiling of these roots revealed extensive changes to plant metabolism. 3) Cell wall composition: The efficiency of converting biomass to fermentable sugars is a function of cell wall composition, which can be modified by exploiting natural genetic variation, chemically induced mutants, and transgenic approaches. We have shown up to 30% improvement in the yield of fermentable sugars from biomass by using mutants with altered cell wall composition, cloned the underlying genes, and explained the impact of the mutations via structural analyses, including X-ray crystallography. Detailed understanding of the catalytic mechanisms of these enzymes is now forming the basis for protein engineering studies in which metabolic pathways can be reconfigured to meet specific applications.
This presentation will highlight the main findings of this multidisciplinary approach to dissect these complex traits.