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Research Interests

I am interested in understanding how transcriptional activators work in plants; in particular, those that work at environmental and/or stress responsive promoters. The underlying question is, how do these proteins, which often work at DNA target sites quite far removed from the transcription start site, bring about the huge increases in transcription that they do? For environmentally responsive genes in which the gene product directly affects the survival of that plant in that environment, this understanding will likely have far reaching implications for plant breeding programs where the goal is to increase the level of environmental stress tolerance of the plant. This study entails identifying those players functioning at such promoters and constructing a model of how they interact with each other and with the DNA to "activate" transcription. While significant bodies of work in yeast and other non-plant eukaryotic systems have described transcriptional activators and numerous of their associated proteins, fundamental knowledge of how transcriptional activators bring about the huge increases in gene expression of those genes affected largely remains unclear.

Using the low temperature cis-acting element, the C-repeat (CRT/DRE) from an Arabidopsis COR (cold-responsive) gene promoter as "bait" in a yeast one-hybrid screen, I isolated the acidic transcriptional activator CBF1 (CRT/DRE binding factor 1). More recent experiments have demonstrated that constitutive overexpression of CBF1 in transgenic Arabidopsis results in the accumulation of the COR gene transcripts in the absence of any low temperature stimulus and this is associated with an increased freezing tolerance of those transgenic plants. A key question now is: how does CBF1 redirect the nuclear transcription apparatus to the COR gene promoter? To answer this question I am taking a multifaceted approach: (1) identification, through searching the Arabidopsis database for homologs to known transcriptional activation facilitators from other eukaryotic systems and characterizing their role in CBF1 mediated transcriptional activation; (2) mutagenesis and subsequent genetic screening for mutants affected in their ability to interact with and fully potentiate activation by CBF1; and (3) biochemical copurification from plants of nuclear factors complexed with CBF1.

Knowing how CBF1 activates transcription reaches beyond just understanding how it induces expression of the COR genes. The striking evolutionary conservation of the low temperature cis-acting element from the Arabidopsis COR gene promoters with the low temperature cis-acting elements found in the promoters of numerous diverse plant taxa together with the accumulating evidence that CBF1 homologs exist in these other plant species strongly supports the premise that a similar mode of action by a CBF1 homolog in these other plant species works to protect the plant against freeze injury. Given the limitations on plant productivity by abiotic stresses in agricultural systems and the central role CBF1 has in the response to abiotic stress in Arabidopsis, a thorough characterization of its mechanism of action in Arabidopsis should significantly aid in both increasing our understanding of the process in all plants and our ability to increase the environmental stress tolerance of all economically importants plants.

Selected References

• Stockinger, E.J., Gilmour, S.J., and Thomashow, M.F. (1997) Arabidopsis thaliana CBF1 encodes an AP2 domain containing transcriptional activator that binds to the C-repeat/DRE, a cis-acting DNA regulatory element that stimulates transcription in response to low temperature and water deficit. Proc. Natl. Acad. Sci. U.S.A. 94: 1035-1040.
• Gilmour, S.J., Zarka, D.G., Stockinger, E.J., Salazar, M.P., Houghton, J.M. and Thomashow, M.F. (1998) Low temperature regulation of the Arabidopsis CBF family of AP2 transcriptional activators as an early step in cold-induced COR gene expression. Plant J. 16: 433-442.

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