Abstract
The most popular CaMV 35S promoter used for the construction of transgenic plants is a constitutive promoter. The use of conditionally expressed promoters would be a better option as the energy towards expression would be accounted for when the need for expression is indicated. The Acacia nilotica has been known to sustain severe moisture stress. The ALDH7 gene has been reported to be an antiquitin. The PCR amplicon for the ALDH7 promoter from A. nilotica was obtained and sequenced from both the ends to decipher nucleotide sequence. Nucleotide sequence analysis of the A. nilotica ALDH7 promoter indicated the presence of a response element. The nucleotide analysis using PLACE indicated presence of the ACGT, drought and salinity stress response element whereas NNPP indicated existence of seven transcriptional start sites and TSSP indicated presence of two promoters. The PCR amplified ALDH7 promoter of A. nilotica was cloned into a binary vector carrying a promoter-less GUS cassette. Thus, the GUS gene could be expressed under the influence of the A. nilotica ALDH7 promoter. Transgenic tobacco plants expressing the GUS gene under the A. nilotica ALDH7 promoter were constructed. Using histochemical staining, the GUS gene expression levels in transgenic tobacco plants during moisture stress and under irrigation were studied. Histochemical staining experiments demonstrated that the GUS gene in transgenic plants was expressed only during moisture stress and remained unexpressed while irrigation was maintained. In contrast, transgenic tobacco plants expressing the GUS gene under the CaMV 35S promoter were found to be constitutive. The histochemical studies also indicated that the GUS expression was stable at least for two generations. Studies of the gene indicated that transgene segregation was in agreement with that of a monogenic trait described by Mendelian inheritance. The ALDH7 promoter of A. nilotica is a conditionally expressible promoter, expressed during moisture stress and suppressed during irrigation.
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