ARS | Publication request: Er-Localized Omega-3 Fatty Acid Desaturases Are Short-Lived Proteins That Contain Degradation Signals in Their N Termini

Submitted to: Meeting Abstract
Publication Type: Abstract
Publication Acceptance Date: April 15, 2005
Publication Date: June 10, 2005
Citation: Dyer, J.M., Bryan, J., Bourassa, L., Shockey, J.M., and Mullen, R.T. 2005. ER-localized omega-3 fatty acid desaturases are short-lived proteins that contain degradation signals in their N termini (abstract). 2005 Biochemistry and Molecular Biology of Plant Fatty Acids and Glycerolipids Symposium, Abstract A3, page 6, June 10-14, Fallen Leaf Lake, CA. 2005:17

Technical Abstract: ER-localized omega-3 fatty acid desaturases (FAD3s) play a central role in plant lipid metabolism by providing polyunsaturated fatty acids for both cellular membranes and storage oil triglycerides. FAD3s also participate in the adaptation of plants to chilling stress, a process that results in an increase in the proportion of polyunsaturated fatty acids in cellular membranes. Evidence acquired to date suggests that the FAD3s are regulated primarily at the post-transcriptional level, although the details of this process have not been clearly defined. To gain insight to potential regulatory mechanisms of ER-localized FAD3s, we expressed two different FAD3 genes in yeast cells and characterized their protein steady-state amounts and half-lives. We selected the tung (Vernicia fordii) and Brassica napus FAD3 genes for this study because the enzymes are 70% identical, yet the tung enzyme produces a 10-fold higher amount of linolenic acid in yeast cells when compared to the Brassica enzyme. Consistent with these observations, quantitative western blotting of yeast lysates revealed that the tung FAD3 protein was present in significantly higher amounts and had a longer half-life than the Brassica FAD3 protein. Furthermore, swapping the amino termini of these two proteins resulted in a rapid degradation of the tung enzyme and stabilization of the Brassica enzyme, indicating that the Brassica sequence contained a putative degradation signal that was both necessary and sufficient for imparting a short half-life to the protein. The Brassica FAD3 protein half-life could also be increased by cultivation of yeast cells at cooler growth temperatures, and microarray analysis was used to identify at least one yeast gene that was specifically involved in this process. Implications for the regulation of FAD activity in plants are discussed.