Submitted to: Lipids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2006
Publication Date: 3/1/2007
Citation: Chen, G.Q., Turner, C., He, X., Nguyen, T.T., McKeon, T.A., Chingcuanco, D.L. 2007. Expression Profiles of Genes Involved in Fatty Acid and Triacyblycerol Syntheses in Castor Bean (Ricinus communis L.). Lipids. 41:263-274. Interpretive Summary: The castor plant (Ricinus communis) is a perennial shrub mainly cultivated in tropical and subtropical areas of India, China and Brazil as an oilseed crop. Its seeds accumulate 60% oil in the form of triacylglycerol (TAG) that serves as a major energy reserve for seed germination and seedling growth. Castor oil is unique in that 90% of its fatty acid content is ricinoleate, 12-hydroxyoleic acid. Castor oil is a vital industrial raw material for numerous products such as cosmetics, paints, coatings, plastics and anti-fungal products. One of the problems associated with castor seeds is that they contain the toxin ricin and hyper-allergenic 2S albumins that are detrimental to growers and processors. Therefore it is highly desirable to develop a safe source for castor oil production. Current efforts on metabolic engineering of new oilseeds have been focused on searching for regulatory factors or genes for enzymes that may up-regulate multiple activities or entire pathways leading to oil biosynthesis. Therefore, knowledge of expression of multiple genes and their regulation during castor oil biosynthesis is needed to further understand the regulatory mechanisms controlling castor oil metabolism. In this paper, we survey the available castor sequences in National Center for Biotechnology Information to identify 12 genes that participate in different steps of the pathways leading to fatty acid and TAG syntheses. Our results 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 for safe castor oil production.
Technical Abstract: Castor seed triacylglycerols (TAGs) contain 90% ricinoleate (12-hydroxy-oleate) which has numerous industrial applications. Due to the presence of the toxin ricin and potent allergenic 2S albumins in seed, it is desirable to produce ricinoleate from temperate oilseeds. To identify regulatory genes or genes for enzymes that may up-regulate multiple activities or entire pathways leading to the ricinoleate and TAG syntheses, we have analyzed expression profiles of twelve castor genes involved in fatty acid and TAG syntheses using quantitative reverse transcription-polymerase chain reaction technology. A collection of castor seeds with well-defined developmental stages and morphologies was used to determine the levels of mRNA, ricinoleate and TAG. The syntheses of ricinoleate and TAG occurred when seeds progressed to stages of cellular endosperm development. Concomitantly, most of the genes increased their expression levels, but showed various temporal expression patterns and different maximum inductions ranging from 4 fold to 43,000 fold. Clustering analysis of the expression data indicated five gene groups with distinct temporal patterns. We identified genes involved in fatty acid biosynthesis and transport that fell into two related clusters with moderate flat-rise or concave-rise patterns, and others that were highly expressed during seed development that displayed either linear-rise or bell-shaped patterns. Castor diacylglycerol acyltransferase 1 was the only gene having a higher expression level in leaf and a declining pattern during cellular endosperm development. The relationships among gene expression, cellular endosperm development and ricinoleate/TAG accumulation are discussed.