Low-temperature-induced desaturation of fatty acids and expression of desaturase genes in the cyanobacterium Synechococcus sp. PCC 7002.

Changes in response to temperature of lipid classes, fatty acid composition and mRNA levels for acyl-lipid desaturase genes were studied in the marine unicellular cyanobacterium, Synechococcus sp. PCC 7002. The degree of unsaturation of C18 fatty acids increased in cells grown at lower temperature for all lipid classes, and omega 3 desaturation occurred specifically in cells grown at low temperature. While the level of 18:1(9) fatty acids declined, desaturation at the omega 3 position of C18 fatty acids increased gradually during a 12-h period after a temperature shift-down to 22 degrees C. However, the mRNA levels of the desA (delta 12 desaturase), desB (omega 3 desaturase) and desC (delta 9 desaturase) genes increased within 15 min after a temperature shift-down to 22 degrees C; the desaturase gene mRNA levels also rapidly declined within 15 min after a temperature shift-up to 38 degrees C. Therefore, the elevation of mRNA levels for the desaturase genes is not the rate-limiting event for the increased desaturation of membrane lipids after a temperature shift-down. The rapid, low-temperature-induced changes in mRNA levels occurred even when cells were grown under light-limiting conditions for which the growth rates at 22 degrees C and 38 degrees C were identical. These studies indicate that the ambient growth temperature, and not some other growth rate-related process, regulates the expression of acyl lipid desaturation in this cyanobacterium.