Integrated regulation triggered by a cryophyte ω-3 desaturase gene confers multiple-stress tolerance in tobacco

ω-3 fatty acid desaturases (FADs) are thought to contribute to plant stress tolerance mainly through linolenic acid (C18:3)-induced membrane stabilization, but a comprehensive analysis of their roles in stress adaptation is lacking. Here, we isolated a microsomal ω-3 FAD gene (CbFAD3) from a cryophyte (Chorispora bungeana) and elucidated its functions in stress tolerance. CbFAD3, exhibiting a high identity to Arabidopsis AtFAD3, was up-regulated by abiotic stresses. Its functionality was verified by heterogonous expression in yeast. Overexpression of CbFAD3 in tobacco constitutively increased C18:3 in both leaves and roots, which maintained the membrane fluidity, and enhanced plant tolerance to cold, drought, and salt stresses. Notably, the constitutively increased C18:3 induced a sustained activation of plasma membrane Ca(2+)-ATPase, thereby, changing the stress-induced Ca(2+) signaling. The reactive oxygen species (ROS) scavenging system, which was positively correlated with the level of C18:3, was also activated in the transgenic lines. Microarray analysis showed that CbFAD3-overexpressing plants increased the expression of stress-responsive genes, most of which are affected by C18:3, Ca(2+), or ROS. Together, CbFAD3 confers tolerance to multiple stresses in tobacco through the C18:3-induced integrated regulation of membrane, Ca(2+), ROS, and stress-responsive genes. This is in contrast with previous observations that simply attribute stress tolerance to membrane stabilization.