The mitogen-activated protein kinase (MAPK) phosphatases (MKPs) are important negative regulators in the MAPK signaling pathways, which play crucial roles in plant growth, regulation of development and response to environment stresses. Several MAPKs have been reported to be involved in the drought stress response, however, there is no evidence for the specific function of MKPs in drought stress. Here, a putative MKP in rice (Oryza sativa), OsIBR5, was characterized. Expression of OsIBR5 was induced by PEG6000, abscisic acid (ABA) and hydrogen peroxide (H(2)O(2)). Overexpression of OsIBR5 in tobacco plants resulted in hypersensitivity to drought and H(2)O(2) treatments. Drought and ABA-induced stomatal closure was significantly reduced in OsIBR5-overexpressing tobacco plants compared with controls. Moreover, OsIBR5 was found to interact with tobacco MAPKs SIPK and WIPK, and drought-induced WIPK activity was impaired in OsIBR5-overexpressing tobacco plants. These results indicated that OsIBR5 is a MKP which was induced by abiotic stresses and decreased tolerance to drought stress in transgenic tobacco plants.
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