Inducibility of three salinity/abscisic acid-regulated promoters in transgenic rice with gusA reporter gene

The present study evaluates the pattern of stress inducibility of one natural promoter (from rice Rab16A) and two synthetically designed promoters, viz., 4X ABRE (abscisic acid-responsive element, having four tandem repeats of ABRE) and 2X ABRC (abscisic acid-responsive complex, having two tandem repeats of ABRE and two copies of coupling elements), in response to varying concentrations of NaCl and abscisic acid (ABA). Each promoter, independently linked to gusA (that encodes beta glucuronidase, GUS), was introduced into rice (cv. Khitish) through particle bombardment. The T-2 progenies showed integration of gusA in their genome. The accumulation of gusA transcript, driven by each promoter in T-2 transgenics, increased with increasing salt/ABA concentration, with ABA being the better activator of each promoter. Induction in GUS expression, driven by different promoters, was noted on exogenous salt/ABA treatments in a concentration-dependent manner. The maximum induction was observed with 2X ABRC promoter. All the three promoters could drive stress-inducible GUS expression in both vegetative and floral organs. However, prominent GUS expression was noted in the whole seed (both embryo and aleurone layer of endosperm) only by 2X ABRC, whereas it was localized only in the embryo for the other two promoters. Thus, our observation characterizes three efficient salinity/ABA-inducible promoters that have the potentiality in crop biotechnology to drive transgene expression for stress tolerance, whenever abiotic stress is encountered.