Differential temperature regulation of three sunflower microsomal oleate desaturase (FAD2) isoforms overexpressed in Saccharomyces cerevisiae

The oxygen‐independent temperature regulation of three sunflower microsomal oleate desaturase (FAD2) isoforms has been investigated using Saccharomyces cerevisiae cells expressing each FAD2 gene. Yeast cells transformed with the FAD2‐1 gene showed the highest percentage of dienoic acids when they were grown at 10–15 °C. In contrast, the maximal level of dienoic acids for S. cerevisiae cells expressing the FAD2‐2 and FAD2‐3 genes were obtained at 30 and 35 °C, respectively. Temperature shifts in the phase of exponential growth, from 30 to 15 °C or from 15 to 30 °C, produced changes in the final percentage of dienoic acids, mostly in yeast cells transformed with the FAD2‐1 gene, to reach the content corresponding to the new temperature. Low temperature (15 °C) increased the amount of neutral lipids in all transformed yeast cells, mainly because it favored triacylglycerol accumulation. In addition, the FAD2 ‐expressing yeast cells showed a higher polar lipid content than those transformed with the empty vector. Dienoic acids were present in all lipids, although high temperature (30 °C) favored their accumulation in neutral lipids. As the main conclusion, the low thermal stability observed for the major and seed specific isoform (FAD2‐1) is the key factor controlling the direct temperature regulation in sunflower seeds.