Liu, Jianxiang , Srivastava, Renu , Che, Ping , Howell, S.H .
Two membrane-bound bZIP transcription factors of Arabidopsis are activated in response to ER stress.
Stresses leading to the accumulation of misfolded proteins in the ER elicit a highly conserved response in plants called the unfolded protein response (UPR). We have identified two ER-resident bZIP transcription factors in Arabidopsis that are candidates for stress sensors/transducers. The candidates are type II membrane proteins with a cytoplasm-facing b-ZIP domain, a transmembrane segment, and a lumen-facing region with a canonical S1P cleavage site. One of the sensors/transducers, AtbZIP17, is activated by salt stress while another, AtbZIP28, is activated in response to treatment by tunicamycin. Following salt or tunicamycin stress, the respective bZIP sensors/transducers are translocated to the Golgi where they are processed by AtS1P, a subtilisin-like serine protease. To show that AtS1P directly targets AtbZIP17 and AtbZIP28, cleavage of the transducers was demonstrated in an in vitro pull-down assay using agarose bead-immobilized AtS1P. A fluorogenic peptide representing the canonical S1P site present in AtbZIP28 was also shown to be processed specifically by AtS1P. A GFP-tagged N-terminal fragment of AtbZIP17 and AtbZIP28 was translocated to the nucleus in response to the respective stresses. Thus, stress-induced processing releases the N-terminal, cytoplasmic bZIP domain of the sensor, which is then translocated to the nucleus. The released transcriptional activation domains of AtbZIP17 and AtbZIP28 upregulate the expression of corresponding stress response genes in the nucleus. Therefore, the two different stresses are sensed by two different sensors/transducers that activate different sets of genes, which then mitigate the corresponding stress.
This work supported by the NSF 2010 program (IBN0420015).
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Plant Subtilase Database (PSDB)
1 - Plant Sciences Institute, Iowa State University
bZIP transcription factors
Presentation Type: ASPB Minisymposium
Location: International Ballroom South/Hilton
Date: Wednesday, July 11th, 2007
Time: 11:05 AM