Soybean DREB1/CBF‐type transcription factors function in heat and drought as well as cold stress‐responsive gene expression
Soybean (Glycine max) is a globally important crop, and its growth and yield are severely reduced by abiotic stresses, such as drought, heat, and cold. The cis‐acting element DRE (dehydration‐responsive element)/CRT plays an important role in activating gene expression in response to these stresses. The Arabidopsis DREB1/CBF genes that encode DRE‐binding proteins function as transcriptional activators in the cold stress responsive gene expression. In this study, we identified 14 DREB1‐type transcription factors (GmDREB1s) from a soybean genome database. The expression of most GmDREB1 genes in soybean was strongly induced by a variety of abiotic stresses, such as cold, drought, high salt, and heat. The GmDREB1 proteins activated transcription via DREs (dehydration‐responsive element) in Arabidopsis and soybean protoplasts. Transcriptome analyses using transgenic Arabidopsis plants overexpressing GmDREB1s indicated that many of the downstream genes are cold‐inducible and overlap with those of Arabidopsis DREB1A. We then comprehensively analyzed the downstream genes of GmDREB1B;1, which is closely related to DREB1A, using a transient expression system in soybean protoplasts. The expression of numerous genes induced by various abiotic stresses were increased by overexpressing GmDREB1B;1 in soybean, and DREs were the most conserved element in the promoters of these genes. The downstream genes of GmDREB1B;1 included numerous soybean‐specific stress‐inducible genes that encode an ABA receptor family protein, GmPYL21, and translation‐related genes, such as ribosomal proteins. We confirmed that GmDREB1B;1 directly activates GmPYL21 expression and enhances ABRE‐mediated gene expression in an ABA‐independent manner. These results suggest that GmDREB1 proteins activate the expression of numerous soybean‐specific stress‐responsive genes under diverse abiotic stress conditions.
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