Info

ABA ABA

Independent Independent ABA

Transcription Transcription

Trans-elements DREB1/CBF1 DREB2

rd29A promoter Cis-elements

Modification

DRE

ABRE

To resolve the problem of growth retardation, we used the stress inducible rd29A promoter to cause overexpression of DREB1A in transgenic plants (rd29A:DREB1A plants).21 Because the rd29A promoter was stress inducible and contained binding sites for the DREB1A protein, it did not cause expression of the DREB1A transgene at high levels under unstressed conditions; instead, it rapidly amplified expression of the DREB1A transgene only under dehydration, salt, and low temperature stress. The rd29A:DREB1A plants revealed strong stress tolerance even though their growth retardation under normal growing conditions was not significant. Moreover, the growth and the productivity of these plants were almost the same as those of the wild type plants under normal growing conditions.21

On the contrary, the rd29A:DREB1A transgenic plants are more tolerant to the stresses than the 35S:DREB1A plants that exhibited growth retardation under normal growing conditions (Fig. 20.4).21 As the rd29A gene is one of the target genes of the DREB1A protein, the rd29A promoter is more suitable for the tissue specific expression of the DREB1A gene in plants than the 35S CaMV promoter. In the rd29A:DREB1A plants, the target gene products seem to be strongly accumulated in the same tissues that express the products under stress conditions. These results indicate that combination of the DREB1A cDNA with the rd29A promoter would be quite useful for improving drought, salt and freezing stress tolerance in transgenic plants.

In a previous studies, we showed that DRE also functions in gene expression in response to stress in tobacco plants,2,13 which suggests the existence of similar regulatory systems in tobacco and other crop plants. DRE-related motifs have been reported in the promoter region of cold inducible Brassica

Fig. 20.4. Freezing and drought stress tolerance of the 35S:DREB1Ab, 35S:DREB1Ac and rd29A:DREB1Aa transgenic plants. The stress treatments were conducted as described in the text. Control: 3 week old plants growing under normal conditions; Freezing: plants exposed to a temperature of -6°C for 2 days and returned to 22°C for 5 days; Drought: water withheld for 2 weeks. Percentages of surviving plants and numbers of surviving plants per total tested plants are shown under the pictures.

Drought Stress Rd29a

Fig. 20.4. Freezing and drought stress tolerance of the 35S:DREB1Ab, 35S:DREB1Ac and rd29A:DREB1Aa transgenic plants. The stress treatments were conducted as described in the text. Control: 3 week old plants growing under normal conditions; Freezing: plants exposed to a temperature of -6°C for 2 days and returned to 22°C for 5 days; Drought: water withheld for 2 weeks. Percentages of surviving plants and numbers of surviving plants per total tested plants are shown under the pictures.

napus and wheat genes.23,24 These observations suggest that both the DREB1A cDNA and the rd29A promoter can be used to improve the dehydration, salt and freezing tolerance of crops by gene transfer.

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