Date of Graduation

2005

Document Type

Thesis

Degree Type

MS

Committee Chair

Keqiang Wu

Abstract

ERFs (ethylene-responsive element binding factors) belong to a large family of transcription factors that are found exclusively in plants. A small subfamily of ERF proteins can act as transcriptional repressors. The Arabidopsis genome contains eight ERF repressors, namely AtERF3, AtERF4, AtERF7, AtERF8, AtERF9, AtERF10, AtERF11, and AtERF12. The different ERF repressors show differential expression, suggesting that they may have different function. The expression of AtERF4 can be induced by ethylene, jasmonic acid, or abscisic acid. AtERF7 can be induced by abscisic acid only. Using a transient expression system, we demonstrated that AtERF4 and AtERF7 can function as transcriptional repressors. By using green fluorescent protein fusion, we demonstrated that AtERF4 and AtERF7 accumulated in the nuclear bodies of Arabidopsis cells. Expression of 35S::AtERF4-GFP and 35S::AtERF7-GFP in transgenic Arabidopsis plants conferred the ethylene-insensitive phenotype. Compared to wild-type plants, 35S::AtERF4-GFP and 35S::AtERF7-GFP transgenic plants had decreased sensitivity to abscisic acid. In addition, 35S::AtERF4-GFP and 35S::AtERF7-GFP transgenic plants showed hypersensitive to sodium chloride, drought and freezing. The expression of the abscisic acid responsive genes, ABI2, rd29B and rab18, was decreased in the 35S::AtERF4-GFP and 35S::AtERF7-GFP transgenic plants. Our study provides evidence that AtERF4 and AtERF7 are negative regulators capable of modulating abscisic acid responses. The GCC-box is a cis-acting sequence (AGCCGCC) that is found in the promoters of many pathogen-responsive genes in plants. The GCC-box has been shown to function as an ethylene-responsive element(s) that is sufficient for the regulation of transcription by ethylene. Several members of ERF proteins bind specifically to the sequence AGCCGCC through the conserved ERF domain. Here, we identified and classified all GCC-box containing genes in Arabidopsis. We found that there are 867 genes containing a GCC-box within 1000 bp upstream of their start codons. Of these genes, 656 are represented in the ATH1 Arabidopsis GeneChip from Affymetrix and can be classified into five major classes: metabolism, defense and stress response, signal transduction, transcription, and cellular organization. About 18% of these genes have been classified into the defense and stress category. In addition to their roles in defense and stress responses, our analysis indicated that the GCC-box containing genes may also be involved other cellular processes.

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