Minisymposium 4: Oxidative stress

Abs # 14001: Arabidopsis OXS2 is a transcription factor in the oxidative stress response

Presenter:	Robert, Blanvillain , robertab@uclink.berkeley.com
Authors	Robert, Blanvillain  (A)   David, OW  (A)
Affiliations:	(A): Plant Gene Expression Center, UC Berkeley, USDA

The growth and reproduction of plants, which are sedentary organisms, are highly dependent on their ability to weather the environment. Sudden and extreme changes in external conditions require immediate and effective biochemical responses. In an attempt to define the molecular basis of environmental stress tolerance, a functional selection strategy was conducted in the fission yeast Schizosaccharomyces pombe. Plant cDNA libraries were expressed in S. pombe and screened for an enhanced ability to tolerate diamide-induced oxidative stress. Here, we report the identification of an Arabidopsis thaliana oxidative stress tolerance gene, OXS2. This gene belongs to a five-member family of C3H zinc-finger protein genes, with each protein member possessing a canonical C2-H2-type zinc finger, two C3-H-type zinc-fingers, and an ANKYRIN motif. The OXS2 protein, when fused to a GAL4 DNA binding domain, can activate the transcription of a promoter with an upstream GAL4 binding site. Full transcription activation requires a poly-glutamine rich region within the OXS2 activation domain. Interestingly, OXS2 can also autoactivate its own promoter, and this correlates with the elevated accumulation of OXS2 mRNA during oxidative stress. A selection and amplification binding assay (SAAB) revealed a nine-base-pair CT-rich target sequence that is also present in the OXS2 promoter. OXS2 protein is also regulated at the level of subcellular localization, as OXS2-enhanced green florescence protein fusions showed movement from the cytoplasm to the nucleus during stress. Deletion analysis of the OXS2 protein delimited a 17aa nuclear export signal (NES) related to the published consensus. This nucleocytoplasmic shuttling is sensitive to leptomycin B, a specific inhibitor of Exportin I (XPOI or Crm1) that blocks the interaction between Exportin I and the cargo protein NES. Nuclear accumulation, along with the auto-activation of its own gene, accounts for the higher accumulation of OXS2 mRNA during stress. Transgenic plants expressing OXS2 from the 35S promoter accelerates a commonly recognized survival strategy during stress, the redirection from vegetative growth to flowering. Taken together, these results lead to a model where oxidative stress causes the inactivation of Exportin-mediated export and hence nuclear accumulation of OXS2, the autoactivation of its own gene, followed by the activation of a stress-induced flowering pathway.