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The oilseed plant castor bean (Ricinus communis) is a member of the family Euphorbiaceae. Cassava (Manihot esculenta), rubber tree (Hevea brasiliensis), ornamental poinsettias (Euphorbia pulcherrima), and the invasive weed leafy spurge (Euphorbia esula) are other important members of this family that includes nearly 250 genera comprising 6,300 species.

Castor oil is extracted from R. communis seeds and has multiple applications. Castor bean seed triacylglycerols (TAG) contain 90% ricinoleate (12-hydroxy-oleate) and is the only commercial source of hydroxy-fatty acid, an unusual fatty acid. The hydroxy group has special chemical and physical properties that make castor oil a vital industrial raw material for numerous products, including high quality lubricants, paints, coatings, plastics, soaps, medications for skin affections and cosmetics. Castor oil can be used as lubricity additive to replace sulfur-based lubricity components in petroleum diesel helping to reduce sulfur emissions.

Castor bean seeds also contain high concentrations of a type 2 ribosome-inactivating enzyme, ricin, which is one of the deadliest natural poisons. Therefore, there is also an interest in castor bean from the bio-defense point of view. The world annual castor oil production in 2004-5 was around 0.5 million tons but, due to the presence of ricin, castor bean is not grown commercially in the U.S. Rather, the U.S. is amongst the world largest importers of castor oil and its derivatives. Deeper understanding of the castor bean biology will allow improvements in castor oil production without the problem of ricin, either by engineering castor bean or other oilseed plants. We have sequenced and assembled a 4X draft of the ~400 Mbp castor bean genome using a whole genome shotgun strategy. In addition, ~50,000 ESTs from different tissues have been produced to help gene discovery and annotation. Preliminary comparisons between castor bean genes and ESTs from other available Euphorbiaceae species, showed that cassava shares the highest sequence similarity with castor bean. With the on-going DOE-JGI cassava genome sequencing project, castor bean and cassava will constitute a valuable comparative genomics system.

This project is funded by the NIAID-NIH, through the Microbial Genome Sequencing Center at TIGR (http://www.tigr.org/msc).