Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/19/2008
Publication Date: 9/17/2009
Citation: Chen, G.Q. 2009. Seed Development in Castor (Ricinus communis L.): Morphology, Reserve Synthesis and Gene Expression. In: Hayworth, G, editor. Reliability Engineering Advances. Hauppauge, NY:Nova Science Publishers. p. 305-330. Interpretive Summary: Castor oil is the only commercial source of ricinoleate, 12-hydroxyoleic acid. The hydroxy group imparts unique chemical and physical properties that make castor oil a vital industrial raw material for numerous products such as lubricants, cosmetics, paints, coatings, plastics and anti-fungal products. Now with the growth of biodiesel, castor oil has an expanding new use. Castor oil biodiesel eliminates the need of adding sulfer-based lubricity components in conventional diesel fuel, significantly reducing air pollution. However, the presence of ricin toxin and hyper-allergenic 2S albumins in seed poses health concern during its cultivation and processing. In order to develop a safe source of castor oil, we conducted a series of seed developmental studies in castor. This chapter illustrates our results and findings which are critical to metabolic engineering of ricinoleate production in transgenic oil seeds, as well as genetic suppression of ricin and 2S albumin in castor.
Technical Abstract: Castor (Ricinus communis L.) is a non-eatable oilseed crop producing seed oil comprising 90% ricinoleate (12-hydroxy-oleate) which has numerous industrial uses. However, the production of castor oil is hampered by the presence of noxious seed storage proteins, the toxin ricin and hyper-allergenic 2S albumins. 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. To understand the mechanisms underlying the synthesis of ricin, 2S albumins and ricinoleate/oil, we conducted a series of seed development studies in castor, including endosperm morphogenesis, storage compound accumulation and gene expression. The entire course of seed development can be divided into four stages, which are recognizable by distinct seed coat color and volume of cellular endosperm. Synthesis of ricin, 2S albumins and oil occur during cellular endosperm development. Concomitantly, we observed increased transcript levels of 14 genes involved in synthesis of ricin, 2S albumin and oil, but with various temporal patterns and different maximal inductions ranging from 2 fold to 43,000 fold. The results indicate that gene transcription exerts a primary control in castor reserve biosyntheses. Based on the temporal pattern and level of gene expression, we classified these genes into five groups. These transcription-profiling data provide not only the initial information on promoter activity for each gene, but also a first glimpse of the global patterns of gene expression and regulation, which are critical to metabolic engineering of transgenic oilseeds. Since all these studies are illustrated based on a well-defined time course, the results also provide integrative information for understanding the relationships among endosperm morphogenesis, reserve biosynthesis and gene expression during castor seed development.