Plant Physiology Preview
Published on June 23, 2006; 10.1104/pp.106.080697
Received March 21, 2006
Returned for revision May 9, 2006
Accepted June 16, 2006
Activation of Ntf4, a tobacco MAPK, during plant defense response and its involvement in hypersensitive response-like cell death
Dongtao Ren , Kwang-Yeol Yang , Guo-Jing Li , Yidong Liu , and Shuqun Zhang *
State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100094, China; Department of Biochemistry, University of Missouri-Columbia, 109 Life Sciences Center, Columbia, MO 65211, USA
Department of Biochemistry, University of Missouri-Columbia, 109 Life Sciences Center, Columbia, MO 65211, USA; Current address: Department of Plant Biotechnology, College of Agriculture & Life Sciences, Chonnam National University, Gwangju 500-757, Repubilic of Korea
Department of Biochemistry, University of Missouri-Columbia, 109 Life Sciences Center, Columbia, MO 65211, USA; Current address: College of Bioengineering, Inner Mongolia Agricultural University, Huhhot 010018, China
Department of Biochemistry, University of Missouri-Columbia, 109 Life Sciences Center, Columbia, MO 65211, USA
* Corresponding author; email: zhangsh{at}missouri.edu.
Mitogen-activated protein kinase (MAPK) cascades are important signaling modules in eukaryotic cells. They function downstream of sensors/receptors and regulate cellular responses to external and endogenous stimuli. Recent studies demonstrated that SIPK and WIPK, two tobacco MAPKs, are involved in signaling plant defense responses to various pathogens. Ntf4, another tobacco MAPK that shares 93.6% and 72.3% identity with SIPK and WIPK, respectively, was reported to be developmentally regulated and function in pollen germination. We found that Ntf4 is also expressed in leaves and suspension cultured cells. Genomic analysis excluded the possibility that Ntf4 and SIPK are orthologs from the two parental lines of the amphidiploid common tobacco. In vitro and in vivo phosphorylation and activation assays revealed that Ntf4 shares the same upstream MAPKK, NtMEK2, with SIPK and WIPK. Similar to SIPK and WIPK, Ntf4 is also stress responsive and can be activated by cryptogein, a proteinaceous elicitin from oomycetic pathogen Phytophthora cryptogea. Tobacco recognition of cryptogein induces rapid hypersensitive response (HR) cell death in tobacco. Transgenic Ntf4 plants with elevated levels of Ntf4 protein showed accelerated HR cell death when treated with cryptogein. In addition, conditional over-expression of Ntf4, which results in high cellular Ntf4 activity, is sufficient to induce HR-like cell death. Based on these results, we concluded that Ntf4 is multi-functional. In addition to its role in pollen germination, Ntf4 is also a component downstream of NtMEK2 in the MAPK cascade that regulates pathogen-induced HR cell death in tobacco.
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