GmDREB2A;2, a Canonical DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN2-Type Transcription Factor in Soybean, Is Posttranslationally Regulated and Mediates Dehydration-Responsive Element-Dependent Gene Expression    

Abstract

Soybean (Glycine max) is an important crop around the world. Abiotic stress conditions, such as drought and heat, adversely affect its survival, growth, and production. The DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN2 (DREB2) group includes transcription factors that contribute to drought and heat stress tolerance by activating transcription through the cis-element dehydration-responsive element (DRE) in response to these stress stimuli. Two modes of regulation, transcriptional and posttranslational, are important for the activation of gene expression by DREB2A in Arabidopsis (Arabidopsis thaliana). However, the regulatory system of DREB2 in soybean is not clear. We identified a new soybean DREB2 gene, GmDREB2A;2, that was highly induced not only by dehydration and heat but also by low temperature. GmDREB2A;2 exhibited a high transactivation activity via DRE and has a serine/threonine-rich region, which corresponds to a negative regulatory domain of DREB2A that is involved in its posttranslational regulation, including destabilization. Despite the partial similarity between these sequences, the activity and stability of the GmDREB2A;2 protein were enhanced by removal of the serine/threonine-rich region in both Arabidopsis and soybean protoplasts, suggestive of a conserved regulatory mechanism that involves the recognition of serine/ threonine-rich sequences with a specific pattern. The heterologous expression of GmDREB2A;2 in Arabidopsis induced DREregulated stress-inducible genes and improved stress tolerance. However, there were variations in the growth phenotypes of the transgenic Arabidopsis, the induced genes, and their induction ratios between GmDREB2A;2 and DREB2A. Therefore, the basic function and regulatory machinery of DREB2 have been maintained between Arabidopsis and soybean, although differentiation has also occurred.

Functionality of soybean CBF/DREB1 transcription factors

“…None of the soybean genes similar to AtDREB2 or 3 were up-regulated at 1 h cold treatment, indicating that the GmCBF/DREB1 gene group are the immediate cold responsive genes acting as primary cold transcription factors ( Figure 3). By 24 h of cold treatment, transcripts of four DREB2-like genes (Glyma18g43750, Glyma14g06080, Glyma02g42960, and Glyma10g07756) were significantly accumulated, consistent with the previous observations of GmDREB2A;1 (Glyma02g42960) and GmDREB2A;2 (Glyma14g06080) cold responses [24]. The cold transcription factors, SCOF-1 (Glyma17g35430) and SCOF-1 like genes (Glyma06g04840, Glyma04g04760, Glyma20g26940, Glyma14g09760 and Glyma10g40400) were also significantly upregulated within 1 h of cold treatment and most sustained a significantly high level of transcript at 24 h ( Figure S1).…”

“…Consistent with these observations, some members of the DREB2 family, both in Arabidopsis [12] and in soybean [24], are more strongly up-regulated in response to dehydration and salt stress than cold stress.…”

“…At least 44 DREB candidates ( Figure 1) were found including those previously described such as GmDREB2 [30] and GmDREB2A;2 [24].…”

“…Overexpression of AtDREB1A or AtDREB2A in Arabidopsis transgenic plants induces the expression of cold responsive genes such as RD29a and COR47 without exposure to low temperature [18][19][20]. The accumulation of downstream genes mediated by CBF/DREB1 genes, increases abiotic stress tolerances to freezing, dehydration, and high salt [14,[20][21][22][23][24]. In cold-intolerant tomato, the transgenic expression of AtCBF1 gene increased cold regulated genes [25] [ 26,27] and the expression of AtCBF1 in tomato increases freezing tolerance [26][27][28].…”

Arabidopsis DPB3-1, a DREB2A Interactor, Specifically Enhances Heat Stress-Induced Gene Expression by Forming a Heat Stress-Specific Transcriptional Complex with NF-Y Subunits

“…In the 35S:DPB3-1 plants, 110 genes were upregulated more than 2-fold in comparison to vector control plants. Among the 110 genes, 24 genes were also upregulated in 35S:DREB2A CA plants (Sakuma et al, 2006b;Mizoi et al, 2013), and 14 genes were induced after 5 h of heat stress at 37°C (Sakuma et al, 2006b) (Supplemental Data Set 2). HsfA1s are master regulators of the heat shock response in Arabidopsis, and most heat stressinducible genes, including DREB2A, are drastically impaired in quadruple hsfa1 mutants (hsfa1a hsfa1b hsfa1d hsfa1e) (Liu et al, 2011;Yoshida et al, 2011).…”