Temperature-regulated mRNA accumulation and stabilization for fatty acid desaturase genes in the cyanobacterium Synechococcus sp. strain PCC 7002

Abstract

Cyanobacteria acclimate to low-temperature conditions by desaturating their membrane lipids. The desB (ω3 desaturase) and desC (Δ9 desaturase) genes of Synechococcus sp. strain PCC 7002 were cloned and characterized, and the expression of the desA (Δ12 desaturase), desB and desC genes was studied as a function of temperature. The steady-state mRNA abundance for the desA gene was threefold higher in cells grown at 22°C than in cells grown at 38°C. desB transcripts were not detected at 38°C, but were abundant in cells grown at 22°C. Levels of desC mRNA were similar at both growth temperatures. The mRNA levels of each desaturase gene increased within 15 min of a temperature shift-down to 22°C, and mRNA levels recovered within 15 min after a shift-up to 38°C. The cold-induced accumulation of transcripts from the desA and desB genes was suppressed by the addition of chloramphenicol, but the transient elevation of the desC transcript levels at 22°C was not affected by chloramphenicol. The half-lives of the desA and desB mRNAs were significantly longer in cells grown at 22°C than in cells grown at 38°C, but the desC mRNA had a similar half-life at both temperatures. These studies reveal three patterns of temperature requlation for the desaturase genes, whose expression is tightly controlled by a combination of mRNA synthesis and stabilization. These studies demonstrate that elevation of desaturase mRNA levels is not the rate-limiting event during the low-temperature acclimation of cyanobacteria.