Temperature-dependent translational regulation of the ER omega-3 fatty acid desaturase gene in wheat root tips.

The proportion of alpha-linolenic acid (18:3) among the total fatty acids in root tissue increases as the growth temperature decreases. Endoplasmic reticulum omega-3 fatty acid desaturase is responsible for the production of most of the 18:3 in root tissue. In this study, the effect of temperature on expression of the TaFAD3 gene, which encodes endoplasmic reticulum omega-3 desaturase in wheat (Triticum aestivum L. cv. Chihoku), was analysed at the mRNA and protein levels. In wheat root tips grown at 30 and 10 degrees C, the proportions of 18:3 among total fatty acids were 22% and 55%, respectively. The level of TaFAD3 protein in microsomal preparations of the root tips grown at 10 degrees C was approximately 7.5 times higher than that of the root tips grown at 30 degrees C. The increased level of TaFAD3 protein at the lower temperature was accompanied by enhanced association of TaFAD3 mRNA with polyribosomes. In contrast, the level of TaFAD3 mRNA in root tips grown at 10 degrees C was slightly higher than in those grown at 30 degrees C. These results suggest that, in root tips, the increase in the 18:3 level at low temperature is achieved directly by an increase in the amount of TaFAD3 protein, and that temperature-dependent translational regulation of the TaFAD3 gene, rather than its transcriptional regulation, contributes to modulation of the TaFAD3 protein accumulation.