Submitted to: Lipids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2004
Publication Date: 1/11/2005
Citation: He, X., Chen, G.Q., Lin, J.T., Mckeon, T.A. 2005. Regulation of diacylglycerol acyltransferase in developing seeds of castor. Lipids. 39: pp. 865-871
Interpretive Summary: In order to find new uses for vegetable oils in surplus, it is essential to develop alternative uses for them. One approach is to biochemically convert the oil to more valuable products. This paper reports the regulation of diacylglycerol acyltransferase, an enzyme that is essential in making castor oil. Castor oil is a vegetable oil with numerous industrial applications, including bio-based plastics, lubricants, bio-fuel additives and coatings. Currently, the domestic market consumes 110 million pounds of this strategically important oil, and it is all imported. The elucidation of this gene's regulation supports development of biochemical means to produce alternative sources of castor oil. Ultimately, this research will result in domestic capability for castor oil production, expanding the availability of bio-based products.
Technical Abstract: We have previously reported the cloning of castor diacylglycerol acyltransferase (RcDGAT) based on its homology to other plant type 1 DGATs. In order to elucidate the physiological role of the RcDGAT, we have investigated the regulation of RcDGAT expression in developing seeds of castor. The RcDGAT transcript appeared at 12 days after pollination (DAP), reached the highest level at 26 DAP, and declined rapidly after that. However, the RcDGAT protein started to accumulate at 26 DAP, reached its peak at 47 DAP, then remained at this high level until 54 DAP. The significant difference between the expression of mRNA and protein indicates that gene expression of RcDGAT in maturing castor seeds is controlled at the posttranscriptional level. We found that DGAT activity measured in microsomal membranes isolated from seed at different stages of development was parallel to RcDGAT protein level, suggesting DGAT activity is mainly a function of the level of RcDGAT protein. We monitored the TG composition and content during seed development. Compared to the overall rate of TG accumulation, DGAT activity appeared coincidently with the onset of lipid accumulation at 26 DAP; the highest DGAT activity occurred during the rapid phase of lipid accumulation at 40 DAP; and a decline in DGAT activity coincided with a decline in accumulation rate of TG after 40 DAP. The ricinoleate-containing TG content was very low (only 6.71%) in oil extracted from seeds before 19 DAP; however, it increased up to 76.62% of the oil at 26 DAP. The relative amount of triricinolein in oil at 26 DAP was 53 times higher than that at 19 DAP and it was about 76% of the amount present in oil from mature castor seeds. The close correlation between profiles of RcDGAT activity and oil accumulation confirms the role of RcDGAT in castor oil biosynthesis.