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1.  ATHB17 Is a Positive Regulator of Abscisic Acid Response during Early Seedling Growth 
Molecules and Cells  2013;35(2):125-133.
We performed activation tagging screen to isolate abscisic acid (ABA) response mutants. One of the mutants, designated ahs10 (ABA-hypersensitive10), exhibited ABA-hypersensitive phenotypes. TAIL-PCR analysis of the mutant revealed that T-DNA was inserted in the promoter region of the Arabidopsis gene, At2g01430, which encodes a homeodomain-leucine zipper protein ATHB17. Subsequent expression analysis indicated that ATHB17 was activated in ahs10. To recapitulate the mutant phenotypes, we prepared ATHB17 OX lines and investigated their phenotypes. The results showed that ATHB17 confers ABA-hypersensitivity and drought tolerance. On the contrary, ATHB17 knockout lines were ABA-insensitive and drought-sensitive, further demonstrating that ATHB17 is involved in ABA and water-stress responses. Interestingly, the ATHB17 effect on seedling growth in the presence of ABA was observed only during the postgermination seedling establishment stage, suggesting that it functions during a narrow developmental window of early seedling growth.
doi:10.1007/s10059-013-2245-5
PMCID: PMC3887901  PMID: 23456334
abscisic acid (ABA); activation tagging; drought tolerance; HD-Zip protein
2.  Isolation and functional characterization of CE1 binding proteins 
BMC Plant Biology  2010;10:277.
Background
Abscisic acid (ABA) is a plant hormone that controls seed germination, protective responses to various abiotic stresses and seed maturation. The ABA-dependent processes entail changes in gene expression. Numerous genes are regulated by ABA, and promoter analyses of the genes revealed that cis-elements sharing the ACGTGGC consensus sequence are ubiquitous among ABA-regulated gene promoters. The importance of the core sequence, which is generally known as ABA response element (ABRE), has been demonstrated by various experiments, and its cognate transcription factors known as ABFs/AREBs have been identified. Although necessary, ABRE alone is not sufficient, and another cis-element known as "coupling element (CE)" is required for full range ABA-regulation of gene expression. Several CEs are known. However, despite their importance, the cognate transcription factors mediating ABA response via CEs have not been reported to date. Here, we report the isolation of transcription factors that bind one of the coupling elements, CE1.
Results
To isolate CE1 binding proteins, we carried out yeast one-hybrid screens. Reporter genes containing a trimer of the CE1 element were prepared and introduced into a yeast strain. The yeast was transformed with library DNA that represents RNA isolated from ABA-treated Arabidopsis seedlings. From the screen of 3.6 million yeast transformants, we isolated 78 positive clones. Analysis of the clones revealed that a group of AP2/ERF domain proteins binds the CE1 element. We investigated their expression patterns and analyzed their overexpression lines to investigate the in vivo functions of the CE element binding factors (CEBFs). Here, we show that one of the CEBFs, AtERF13, confers ABA hypersensitivity in Arabidopsis, whereas two other CEBFs enhance sugar sensitivity.
Conclusions
Our results indicate that a group of AP2/ERF superfamily proteins interacts with CE1. Several CEBFs are known to mediate defense or abiotic stress response, but the physiological functions of other CEBFs remain to be determined. Our in vivo functional analysis of several CEBFs suggests that they are likely to be involved in ABA and/or sugar response. Together with previous results reported by others, our current data raise an interesting possibility that the coupling element CE1 may function not only as an ABRE but also as an element mediating biotic and abiotic stress responses.
doi:10.1186/1471-2229-10-277
PMCID: PMC3016407  PMID: 21162722

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