Stress-induced expression of an activated form of AtbZIP17 provides protection from salt stress in Arabidopsis

Membrane-associated basic-leucine zipper (bZIP) transcription factors that reside in the endoplasmic reticulum represent a newly described class of plant stress sensor/transducers. The bZIP factors are anchored in endoplasmic reticulum (ER) membranes with their C-terminal tails facing the ER lumen and their N terminii, which contain transcriptional components, facing the cytosol. In response to stress, cytosolic components of the transcription factors are released by proteolysis and move to the nucleus where they promote the up-regulation of stress response genes. One such stress sensor/transducer in Arabidopsis is AtbZIP17, which is activated in response to salt stress. With the aim of enhancing salt tolerance, a constitutively activated form of AtbZIP17, truncated before its membrane-anchor domain, was introduced into transgenic plants. When placed under the control of a constitutive promoter, the activated form of AtbZIP17 up-regulated stress response genes under unstressed conditions, but caused a substantial delay in plant development. When the activated form of AtbZIP17 was placed under the control of stress-inducible promoter, development was normal under unstressed conditions. Under salt stress conditions, the stress-inducible expression of the activated AtbZIP17 enhanced salt tolerance as demonstrated by chlorophyll bleaching and seedling survival assays.