| Summary: | 碩士 === 國立臺灣大學 === 植物科學研究所 === 97 === Various abiotic stresses, including drought, high salinity, heat, and cold, affect plant growth. Drought deprived plants of water supply, thus interrupting the normal function. Plants use combination of different physiological and biochemical strategies against drought. Regulation of genes at transcriptional level has been described in response to drought stresses (Shinozaki and Yamaguchi- Shinozaki, 1997; Reddy et al., 2004). According to the microarray data (Seki et al., 2002), we selected At4g28140, which was highly induced to 37.7 fold after drought treatment for 2 hours. This putative transcription factor belongs to AP2/ERF superfamily and has a highly conserved AP2 domain. Our northern blot results revealed that At4g28140 was induced by drought stress, high salinity, and osmotic stress, but not by cold stress and heat stress. In addition, it was demonstrated that At4g28140 was not induced under ABA, ethylene, and methyl jasmonate treatments, and is involved in the ABA-independent pathway. We have found that At4g28140 was expressed in roots, stems, leaves, flowers and siliques, especially in vascular tissues by promoter-GUS assay. Using a fusion protein composed of the full length of At4g28140 coding region and GFP under the control of 35S promoter, subcellular localization study revealed that the GFP fluorescence was detected in the nuclei of onion epidermal cells. The amino acid sequence analysis predicted that this protein contains a nuclear localization signal. Electrophoretic mobility shift assay confirmed that the At4g28140 protein can bind to both GCC box (-AGCCGCCAC-) and DRE/CRT element (-TACCGACAT-) in the promoter regions of responsive genes. Loss-of-function study which used T-DNA knockout mutant did not show significant differences from wild-type plant. The finding suggested some functional redundancy of other stress-related genes. With respect to overexpression approach, 35S::HA-At4g28140 transgenic plants failed to produce detectable protein due to proteasome activity. In conclusion, in this study we provided evidence to show At428140 is an ABA-independent, dehydration-inducible transcription factor. Along with the overexpression approach deleting the C-terminal of At4g28140 (performed by Jui-Hung Chen), this gene may function a positive regulator in drought stress response pathway.
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