Comparative functional analysis of two wheat Na⁺/H⁺ antiporter SOS1 promoters in Arabidopsis thaliana under various stress conditions

The bread wheat TaSOS1 has been previously shown to be induced by salt stress treatment. To further investigate the regulation of the TaSOS1 gene, the two genomic fragments Pr_SOS1-AB and Pr_SOS1-D have been isolated and sequenced. Pr_SOS1-AB and Pr_SOS1-D are the promoter regions of SOS1 alleles, which are localised on genomes A and/or B, and on genome D, respectively. Sequence analysis of these two promoters revealed the presence of cis-regulatory elements which could be required for abiotic stress and abscisic acid (ABA) responsiveness. Histochemical assays of stably transformed Arabidopsis T3 plants showed that Pr_SOS1-AB and Pr_SOS1-D are active in this heterologous system, and their activities were almost the same at early developmental stages (4-, 8- and 12-day-old transgenic Arabidopsis seedlings). Nevertheless, β-glucuronidase (GUS) activity was detected only in plants carrying the Pr_SOS1-AB–gusA construct grown for 20 or 30 days. Furthermore, in these plants, the application of abiotic stress produced an accumulation in gusA transcripts. Taken together, these results show that, in this heterologous dicot system and under normal growth conditions, Pr_SOS1-AB and Pr_SOS1-D are age-dependent and organ-specific promoters. However, in the presence of different stress conditions, the activities of these two promoters became different and only Pr_SOS1-AB is an abiotic stress-inducible promoter at different developmental stages. Thus, Pr_SOS1-AB can be used for the development of abiotic stress-tolerant transgenic plants.