Abstract
The DREB (dehydration-responsive element binding)-type transcription factors regulate the expression of stress-inducible genes by binding the DRE/CRT cis-elements in promoter regions. The upstream transcription factors that regulate the transcription of DREB transcription factors have not been clearly defined, although the function of DREB transcription factors in abiotic stress is known. In this study, an abscisic acid (ABA)-responsive DREB-binding protein gene (SiARDP) was cloned from foxtail millet (Setaria italica). The transcript level of SiARDP increased not only after drought, high salt, and low temperature stresses, but also after an ABA treatment in foxtail millet seedlings. Two ABA-responsive elements (ABRE1: ACGTGTC; ABRE2: ACGTGGC) exist in the promoter of SiARDP. Further analyses showed that two ABA-responsive element binding (AREB)-type transcription factors, SiAREB1 and SiAREB2, could physically bind to the ABRE core element in vitro and in vivo. The constitutive expression of SiARDP in Arabidopsis thaliana enhanced drought and salt tolerance during seed germination and seedling development, and overexpression of SiARDP in foxtail millet improved drought tolerance. The expression levels of target genes of SiARDP were upregulated in transgenic Arabidopsis and foxtail millet. These results reveal that SiARDP, one of the target genes of SiAREB, is involved in ABA-dependent signal pathways and plays a critical role in the abiotic stress response in plants.
Highlights
The growth of plants and productivity of crops are limited by environmental stresses, such as drought, high salinity, soils, and low temperatures
SiAREB1 and SiAREB2 strongly activated β-galactosidase compared with the negative control (Supplementary Figure S4 at JXB online). These results suggest that SiAREB1 and SiAREB2 are ABA-responsive element binding (AREB)-type transcription factors associated with abiotic stress in foxtail millet
With the addition of the unlabelled core probe, the signal was reduced, but the addition of the mutant probe did not interfere with binding. These results indicate that SiAREB1 and SiAREB2 bind to the ABRE2 element in the promoter of SiARDP
Summary
The growth of plants and productivity of crops are limited by environmental stresses, such as drought, high salinity, soils, and low temperatures. To respond and adapt to these stresses, a large number of specific genes are induced, such as molecular chaperones, osmotic adjustment proteins (Tamura et al, 2003), ion channels (Ward and Schroeder, 1994) and others (Ingram and Bartels, 1996; Thomashow, 1999). Most of these functional proteins are regulated by specific transcription factors (Zhu, 2002; Chinnusamy et al, 2004; Bartels and Sunkar, 2005; Yamaguchi-Shinozaki and Shinozaki, 2006). The AREB transcription factors respond mainly to drought and high salinity stresses and are involved in the regulation of gene expression in the ABA-dependent signal transduction pathway (Finkelstein et al, 2002; Fujita et al, 2005)
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