In this article we will discuss about the transgenic strategy of stress in plants.
In Arabidopsis, overexpression of cDNA encoding DREB1 and DREB2 triggered expression of many stress tolerance genes under normal growing conditions. Thus, transgenic strategy resulted in increased tolerance to drought, salinity and cold stress. Researchers from Japan International Research Center for Agricultural Science (JIRCAS) identified 12 stress-inducible genes which are targeted by DREBIA transcription factor protein.
In the transgene construct DREBIA) was driven under the control of Camv 35S promoter (35S:DREB1A). In the notable observation, all the transgenic plants carrying 35S:DREB1A transgene exhibited severe retardation under normal growth condition. This negative effect is probably due to different levels of expression of DREBIA transgenes.
Over production of transcription factor proteins resulted in the expression of all stress inducible target genes, rd29A, rdl7, cor 6.6, cor 15a, erd 10 and kinl. Under normal conditions, plants under this situation suffer heavily due to unnecessary drenching of energy for the production of several hundreds of proteins. This problem was effectively tackled by using stress inducible rd 29A promoter.
In an extended transgenic strategy DREBIA gene expressed under the control of stress inducible rd 29A promoter provides protection and shows minimal effect on plant growth. In addition, it provides high degree of tolerance to stress condition rather when it is expressed under 35S Camv promoter. Since rd 29A promoter is stress inducible, it did not cause expression of the transcription factor gene (DREB).
Under unstressed conditions, instead, it rapidly enhances the expression of DREBIA transgene only under dehydration, high salt and low temperature conditions (Fig. 15.5). Overall rd 29A promoter may be useful to improve stress tolerance of agriculturally important crops by gene transfer. In the earlier transgenic work, Shinozaki and coworkers have amplified signalling pathway by overexpressing gene containing fusion of a DRE-containing promoter with a DREB gene.
This enhances further DREBIA expression in response to stress. This amplified strategy led to strong induction of DRE-containing target genes. Some contrasting experiments show that DREBIA cannot induce the expression of other drought-responsive genes (such as PSCS, erdl, rd22 and rd 29B) which contain no DRE element in their promoter region.