Submitted to: Plant Signaling and Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 16, 2010
Publication Date: March 1, 2011
Citation: Khuu, N., Gidda, S., Shockey, J.M., Dyer, J.M., Mullen, R.T., 2011. The N termini of Brassica and tung omega-3 fatty acid desaturases mediate proteasome-dependent protein degradation in plant cells. Plant Signaling and Behavior. 6(3):422-425. Interpretive Summary: Plants are sessile organisms that must rapidly adapt to changes in their environment in order to survive. Some plants can tolerate high or low temperature extremes, but others, such as cotton, are particularly susceptible to chilling damage, especially at the early stages of plant development during seedling establishment. Damage to crop plants by temperature, therefore, represents a major challenge for agricultural production systems, and knowledge of plant adaptation to temperature is important for improving overall crop performance and yield. In this study, ARS scientists, in collaboration with colleagues at the University of Guelph, have characterized the underlying molecular mechanisms involved in the regulation of a plant enzyme called Fatty acid desaturase-3 (Fad3). This enzyme is extensively regulated in plants to help them adapt to temperature change, and the results described herein provide new insight to how this process occurs. While this information will have the greatest impact in the short-term on scientists interested in understanding basic aspects of temperature adaptation and regulation in plants, the knowledge may also be used by molecular breeders to help identify specific Fad3 genes in crop plants that confer greater resistance to variations in environmental temperature.
Technical Abstract: The regulation of fatty acid desaturase activity in plants is important for determining the polyunsaturated fatty acid content of cellular membranes, which is often rapidly adjusted in plant cells in response to temperature change. Recent studies have demonstrated that the endoplasmic reticulum (ER)-localized omega-3 desaturases (Fad3s) are regulated extensively at the post-transcriptional level by both temperature-dependent changes in translational efficiency, as well as modulation of protein half-life. While the N-terminal sequences of Fad3 proteins were shown to contain information that mediates their rapid, proteasome-dependent protein turnover in both plant and yeast cells, it is currently unknown whether these sequences alone are sufficient to direct protein degradation. In this report, we fused the N-terminal sequences of two different Fad3 proteins to an ER-localized fluorescent protein reporter, consisting of the green fluorescent protein and the ER integral membrane protein cytochrome b5, and then measured (via microscopy) the degradation of the resulting fusion proteins in plant suspension-cultured cells relative to a second, co-expressed fluorescent reporter protein. Overall, the results demonstrate that the N-termini of both Fad3 proteins are sufficient for conferring rapid, proteasome-dependent degradation to an ER-bound marker protein.