ABSTRACT
HKT transporters which mediate Na+-specific transport or Na+-K+ co-transport, play an important role in protecting plants from salinity stress by preventing Na+-over-accumulation in leaves. In this work, a 1508-bp genomic fragment upstream of the TmHKT1;4-A1 translated sequence from Triticum monococcum has been isolated, cloned, and designated as the ''PrTmHKT1;4-A1'' promoter. Sequence analysis of ''PrTmHKT1;4-A1'' revealed the presence of cis-regulatory elements which could be required for abiotic stress and abscisic acid (ABA) responsiveness. The PrTmHKT1;4-A1 sequence was fused to the ß-glucuronidase gene and the resulting construct was transferred into Arabidopsis plants. Histochemical assays of stably transformed Arabidopsis plants showed that PrTmHKT1;4-A1 is active in this heterologous system. Under control conditions, GUS histochemical staining was observed significantly only in leaves of 20-day-old plants. Histological sections prepared at this stage and in leaves revealed activity localized in leaf veins (phloem and bundle sheath). In flowers, GUS activity was detected only in sepals. After 3 days of challenging the plants with salt, dehydration or ABA treatments, the PrTmHKT1;4-A1 transformed Arabidopsis plants showed a substantial increase in the GUS staining in leaves, compared to untransformed plants under the same conditions. Real time qPCR expression analysis of the uidA gene, showed that GusA transcripts were up-regulated by salt, dehydration, and ABA treatments. All together, these results showed that PrTmHKT1;4-A1 is an age-dependent, abiotic-stress-inducible, organ-specific and tissue-specific promoter in a heterologous dicot system.
