Submitted to: Plant and Animal Genome Conference
Publication Type: Abstract Only
Publication Acceptance Date: December 18, 2005
Publication Date: January 12, 2006
Citation: Chen, G.Q., Ahn, Y., Vang, L., Mckeon, T.A. 2006. Profiling of endosperm-regulated gene expression in developing castor seeds to study transcriptional regulation. Plant and Animal Genome Conference. Interpretive Summary: Castor oil contains 90% ricinoleate, an unusual fatty acid with numerous industrial applications. Although the biochemical pathways of ricinoleate biosynthesis have been well studied, the mechanism of such high accumulation of ricinoleate in castor seed remains unknown. In order to better understand the key steps of this biosynthetic process, we have conducted a series of seed development studies including morphogenesis and gene expression.
Technical Abstract: Castor oil contains 90% ricinoleate, an unusual fatty acid with numerous industrial applications. However, castor cultivation and processing generate highly hazardous seed storage proteins, the toxin ricin and hyper-allergenic 2S albumins. To develop a safe source of castor oil, we are using genetic approaches to eliminate the expression of ricin and 2S albumin genes from castor, or to produce castor oil from a temperate oilseed. To understand the regulatory process of storage protein and lipid biosynthesis during castor seed development, we conducted a series of seed developmental studies including endosperm morphogenesis, storage metabolites profiling and gene expression analysis. We established a set of simple criteria, which included two visual markers, seed coat color and endosperm volume, and defined three phases that encompass the course of castor seed development. By quantitative RT-PCR analysis, we investigated the transcript levels of ricin and 2S albumin genes and 14 lipid genes at each stage of seed development. All of the transcripts were induced to higher levels when the endosperm started development. The transcripts reached their peak levels at different stages, displaying various temporal patterns. Furthermore, the level of maximum induction varied dramatically among genes, ranging from 2 fold to >43,000 fold. Based on the temporal pattern and level of gene expression, we classified these genes into six 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 metabolic regulatory network governing biosynthesis of castor storage compounds.