Rice MAPK phosphatase IBR5 negatively regulates drought stress tolerance in transgenic Nicotiana tabacum
Yuge Li ^§, Dongru Feng^§, Deli Zhang^§, Jianbin Su, Yang Zhang, Zhangqun Li, Peiqiang Mu, Bing Liu*, Hong-Bin Wang*, Jinfa Wang

State Key Laboratory of Biocontrol, Key Laboratory of Gene Engineering of the Ministry of Education and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, 510275 Guangzhou, People’s Republic of China.
^§These authors contributed equally to this work.
*Corresponding Author：Tel/ Fax: (+8620) 8403 9179; E-mail: liubing@mail.sysu.edu.cn, wanghb@mail.sysu.edu.cn

Abstract
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 gene in rice (Oryza sativa), OsIBR5, was characterized. Expression of OsIBR5 was induced by PEG6000, abscisic acid (ABA) and hydrogen peroxide (H₂O₂). Overexpression of OsIBR5 in tobacco plants resulted in hypersensitivity to drought and H₂O₂ 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.

Key Words: Drought; MAPKs; MAPK phosphatases (MKPs); OsIBR5; Rice; Stomata