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Title: Expression profile of the genes involved in reserve synthesis in castor (Ricinus communis L.)

item Chen, Grace

Submitted to: Recent Progress in Medicinal Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2009
Publication Date: 6/3/2010
Citation: Chen, G.Q. 2010. Expression profile of the genes involved in reserve synthesis in castor (Ricinus communis L.). Recent Progress in Medicinal Plants.30:271-291.

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, plastics and anti-fungal products [1]. With the growth of biodiesel, castor qualifies as a superior biodiesel crop because of its non-food application, high oil content in seeds (60%) and agronomic traits capable of thriving in arid land. Castor oil biodiesel does not need the heat energy input required by other vegetable oils in the process of transesterfying oil to fuel [2], and it also eliminates the need of adding sulfur-based lubriciting components in conventional diesel fuel, significantly reducing air pollution [3]. However, the presence of ricin toxin and hyper-allergenic 2S albumins in seed poses health concern during castor cultivation and oil processing. To develop a safe source of castor oil, we conducted a series of seed development studies in castor. This review illustrates our results and findings which are useful for the metabolic engineering of ricinoleate production in transgenic oil seeds, as well as genetic suppression of ricin and 2S albumin in castor.

Technical Abstract: Oil derived from the seed of castor (Ricinus communis L.) contains 90% ricinoleate (12-hydroxy-oleate) and has numerous industrial uses. Despite its economic importance, the production of castor oil is hampered by the presence of detrimental seed storage proteins, the toxin ricin and hyper-allergenic 2S albumins. To develop approaches for safe castor oil production, we studied the mechanisms underlying the synthesis of ricin, 2S albumins and ricinoleate/oil. Seed developmental processes including morphogenesis, storage compound accumulation and gene expression were investigated. The entire course of seed development lasts about 61 days and can be divided into 8 stages recognizable by distinct seed coat color and cellular endosperm volume. 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 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. This 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 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.