Cold-induced modulation and functional analyses of the DRE-binding transcription factor gene, GmDREB3, in soybean (Glycine max L.)

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Abstract
DREB (dehydration-responsive element-binding protein) transcription factors have important roles in the stress-related regulation network in plants. A DREB orthologue, GmDREB3, belonging to the A-5 subgroup of the DREB subfamily, was isolated from soybean using the RACE (rapid amplification of cDNA ends) method. Northern blot analysis showed that expression of GmDREB3 in soybean seedlings was induced following cold stress treatment for 0.5 h and was not detected after 3 h. However, it was not induced by drought and high salt stresses or by abscisic acid (ABA) treatment. This response was similar to those of members in the A-1 subgroup and different from those of other members in the A-5 subgroup, suggesting that the GmDREB3 gene was involved in an ABA-independent cold stress-responsive signal pathway. Furthermore, analysis of the GmDREB3 promoter elucidated its cold-induced modulation. A promoter fragment containing bases −1058 to −664 was involved in response to cold stress, and its effect was detected for 1 h after treatment, but a transcriptional repressor appeared to impair this response by binding to a cis-element in the region −1403 to −1058 at 24 h after the beginning of cold stress. Moreover, the GmDREB3 protein could specifically bind to the DRE element in vitro, and activated expression of downstream reporter genes in yeast cells. In addition, overexpression of GmDREB3 enhanced tolerance to cold, drought, and high salt stresses in transgenic Arabidopsis. Physiological analyses indicated that the fresh weight and osmolality of GmDREB3 transgenic Arabidopsis under cold stress were higher than those of wild-type controls. GmDREB3 transgenic tobacco accumulated higher levels of free proline under drought stress and retained higher leaf chlorophyll levels under high salt stress than wild-type tobacco. In addition, constitutive expression of GmDREB3 in transgenic Arabidopsis caused growth retardation, whereas its expression under control of the stress-inducible Rd29A promoter minimized negative effects on plant growth under normal growth conditions, indicating that a combination of the Rd29A promoter and GmDREB3 might be useful for improving tolerance to environmental stresses in crop plants.

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