Cloning and characterization of the Oryza sativa wall-associated kinase gene OsWAK11 and its transcriptional response to abiotic stresses

To examine heavy metal-induced regulatory mechanisms at the transcriptional level, a cell wall-associated receptor kinase (WAK) gene, OsWAK11 and its upstream promoter region (-946/+28) were isolated from Oryza sativa. OsWAK11 expression in response to abiotic stress was examined using a beta-glucuronidase (GUS) gene fusion. Semi-quantitative RT-PCR was used to analyze expression of the OsWAK11 gene. Histochemical detection of GUS was conducted by X-gluc staining methods, and fluorometric measurements of GUS activity were made with 4-methyl umbelliferyl glucuronide (MUG) substrate. The WAK promoter (-946/+28) responded to aluminum chloride, sodium chloride, and copper (II) sulfate with 3.0-, 2.2-, or 6.4-fold induction of GUS activity, respectively. Sodium nitroprusside and wounding treatment stimulated GUS activity. A histochemical analysis revealed strong GUS staining in the hypocotyls, cotyledons, first leaf, and petiole of cotyledons in transgenic tobacco seedlings. Strong GUS staining was also observed in the stigma and ovary of mature flowers, but not in the stamens. OsWAK11 expression is regulated by aluminum, sodium, and copper. The GUS expression observed in transgenic tobacco carrying WAK11 promoter demonstrated significant tissue-specificity. The OsWAK11 promoter was strongly upregulated in response to metals and wounding.