The Arabidopsis redox-sensitive bZIP68 protein: does it function as a redox sensor in the oxidative stress response?

Redox signaling occurs when cellular redox homeostasis is perturbed. Redox signaling has increasingly been recognized as an important mechanism in regulating a variety of biological processes. Adverse environmental conditions often cause overproduction of reactive oxygen species (ROS), which can act as signals in activating the oxidative stress response. Redox signaling is largely mediated by redox-sensitive proteins that undergo oxidative modifications in response to environmental and internal cues that alter cellular redox homeostasis. Some transcription factors have been found to undergo oxidative modification under oxidative stress which alters their activity and/or subcellular localization, leading to activation of stress-responsive genes. The mechanism that regulates the oxidative stress response in plants remains largely unknown.

Through redox proteomics analysis, we recently found that the Arabidopsis basic region/leucine zipper transcription factor AtbZIP68 underwent reversible oxidation at its Cys320 residue in Arabidopsis cells under oxidative stress. We found that bZIP68 is localized in the nucleus under normal conditions but translocates to the cytosol under oxidative stress. We hypothesize that bZIP68 might act as a transcriptional repressor to suppress oxidative stress-responsive genes under normal conditions. Under oxidative stress, it undergoes oxidation which causes its translocation from the nucleus to the cytosol, thereby leading to activation of oxidative stress-responsive genes. In this study, we will use molecular, genetic, and functional genomics approaches to define the molecular mechanism that controls nucleocytoplasmic shuttling of bZIP68 and its transcriptional regulation. We will identify bZIP68’s target genes through chromatin immunoprecipitation followed by high throughput sequencing (ChIP-seq) and by comparison of transcriptomes between the bzip68 mutant and wildtype plants. Additional mutational analysis and the target gene identification will allow us to define biological pathways regulated by bZIP68. The study will reveal whether bZIP68 acts as a redox sensor in regulating the stress response and provide novel insights into the molecular mechanism governing the stress response in plants.