Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 27, 2008
Publication Date: July 20, 2008
Citation: Chen, G.Q. 2008. Searching for a Safe Source of Castor Oil Production through Metabolic Engineering. 18th International Symposium on Plant Lipids, Bordeaux, France, July 20-25, 2008. Interpretive Summary: Castor plant (Ricinus communis L.) produces an unique seed oil with numerous industrial applications. However, castor seed contains toxin ricin and hyper-allergenic 2S albumins detrimental to castor grower and processor. Our project goal is to develop a safe source of castor oil through genetic engineering. The general approach is to generate a safe castor crop by blocking expression of the ricin and 2S albumins in seed. An alternative approach would be transgenic production of ricinoleate from temperate oilseed plants.
Technical Abstract: Castor oil contains 90% ricinoleate (12-hydroxy-oleate) which has numerous industrial uses. The production of castor oil is hampered by the presence of the toxin ricin and hyper-allergenic 2S albumins in its seed. We are developing a safe source of castor oil by two approaches: blocking gene expression of the ricin and 2S albumins in castor seed and engineering a temperate oilseed crop to produce castor oil. In order to understand how ricinoleate/TAG synthesis is regulated, we conducted a series of seed development studies in castor, including endosperm morphogenesis, ricinoleate/TAG accumulation and gene expression. The entire course of seed development can be divided into eight stages with distinctive seed coat color and volume of cellular endosperm. Synthesis of ricinoleate/TAG occurred during cellular endosperm development. Concomitantly, we observed increased transcript levels of 12 genes involved in synthesis of ricinoleate/TAG, but with various temporal patterns and different maximal induction ranging from 4- to 43,000-fold. Clustering analysis of the expression data revealed five gene groups with distinct temporal patterns. These results indicate that gene transcription exerts a primary control in ricinloeate/TAG biosyntheses, and there are different transcriptional regulatory mechanisms involved in the gene expression. With the available sequence information from the castor genome sequence, we have identified and manually annotated ~300 castor lipid genes and their family members by searching the nucleotide database of TIGR gene models with either NCBI published castor lipid genes mRNA sequences or Arabidopsis lipid gene protein sequences from Arabidopsis Lipid Gene Database ( www.planbiology.msu.edu/lipids/genesurvey). We are currently conducting genome-wide analysis of castor lipid genes, including expression profiles and promoter organizations. By characterizing co-expressed genes and conserved promoter motifs, we will be able to identify key genes, promoters and transcription factors as suitable targets for future metabolic engineering of ricinoleate production in transgenic oilseeds, as well as genetic suppression of ricin and 2S albumin in castor.