Evaluation of Drought Stress-Inducible Wsi18 Promoter in Brachypodium distachyon

The rice Wsi18 promoter confers drought-inducible gene expression. This property makes it a useful candidate to drive relevant genes for developing drought resistant traits for different monocot crops. In this study, we showed that the Bradi2G47700 gene, the closest homologue to rice Wsi18, was upregulated in Brachypodium distachyon plants exposed to ABA and mannitol. Wsi18: uidA transgenic B. distachyon plants were produced and then subjected to ABA or mannitol treatment. The expression of uidA in three transgenic lines (line 10, 18 and 37) was significantly upregulated in plants exposed to ABA (fold increases of 5.61 ± 0.98, 2.88 ± 0.75 and 9.13 ± 1.96, respectively) compared to the same transgenic plant lines without treatment. The expression of uidA in two transgenic lines (lines 18 and 37) also showed upregulation when treated with mannitol (fold increases of 4.43 ± 1.07 and 8.47 ± 2.90, respectively) compared to the same transgenic plant lines without mannitol treatment. Moreover, GUS histochemical assay showed increased Wsi18 promoter activity in the leaves and stems of transgenic lines upon treatment with ABA or mannitol. This is the first report of the drought inducible rice Wsi18 promoter being active in B. distachyon which is a model plant for molecular biology research of various monocot plants. Taken together, the results indicate that the Wsi18 promoter and its homologue may be explored as a useful tool for drought stress-inducible gene expression in different monocot crops.