One of the world’s leading grain crops, sorghum is also an important model for tropical grasses of worldwide importance with a collective minimum economic impact of $69 billion U.S. per year. As a model for the tropical grasses, sorghum is a logical complement to Oryza (rice), the first monocot plant to be sequenced. Sorghum is representative of the tropical grasses in that it has “C4” photosynthesis, using a complex combination of biochemical and morphological specializations resulting in more efficient carbon assimilation at high temperatures. By contrast, rice is more representative of temperate grasses, using “C3” photosynthesis.
In addition to its intrinsic value, the sorghum sequence will be a valuable reference for assembling and analyzing the fourfold larger genome of maize (corn), a tropical grass that is the leading U.S. fuel ethanol crop (sorghum is second). Sorghum is an even closer relative of sugarcane, arguably the most important biomass/biofuels crop worldwide with annual production of about 140 million metric tons and a net value of about $30 billion. Sorghum and sugarcane are thought to have shared a common ancestor about 5 million years ago. The two have retained largely common gene order, and some genotypes can still be intercrossed. However, sugarcane has undergone at least two cycles of whole-genome duplication, resulting in a genome larger than that of human and with four- or higher-fold redundancy of most genes. By contrast, sorghum is diploid with a genome about 25% the size of human, maize, or sugarcane.
The Sorghum genus is also noteworthy in that it includes one of the world’s most noxious weeds. The same features that make “Johnson grass” (Sorghum halepense) such a troublesome weed are actually desirable in many forage, turf, and biomass crops that are genetically complex. Therefore, sorghum offers novel learning opportunities relevant to weed biology as well as to improvement of a wide range of other forage, turf, and biomass crops.
Sorghum genome early release data is available via Phytozome.
CSP project participants: Andrew H. Paterson (proposer), John E. Bowers, and Alan R. Gingle (Univ. of Georgia); C. Thomas Hash (Int’l Crops Research Inst. for the Semi-Arid Tropics); Stephen E. Kresovich (Cornell Univ.); Joachim Messing (Rutgers); Daniel G. Peterson (Mississippi State Univ.); and Daniel S. Rokhsar (JGI and UC Berkeley).