Nakagami Hirofumi, Kiegerl Stefan, Hirt Heribert
Institute of Microbiology and Genetics, Vienna Biocenter, University of Vienna, Dr. Bohrgasse 9, A-1030 Vienna, Austria.
J Biol Chem. 2004 Jun 25;279(26):26959-66. doi: 10.1074/jbc.M312662200. Epub 2004 Mar 19.
In common with other eukaryotes, plants utilize mitogen-activated protein kinase (MAPK) cascades to mediate responses to a wide variety of stimuli. In contrast to other eukaryotes, plants have an unusually large number of MAPK components, such as more than 20 MAPKs, 10 MAPK kinases (MAPKKs), and 60 MAPKK kinases (MAPKKKs) in Arabidopsis (MAPK Group (2002) Trends Plant Sci. 7, 301-308). Presently it is mostly unknown how MAPK signaling specificity is generated in plants. Here we have isolated OMTK1 (oxidative stress-activated MAP triple-kinase 1), a novel MAPKKK from alfalfa (Medicago sativa). In plant protoplasts, OMTK1 showed basal kinase activity and was found to induce cell death. Among a panel of hormones and stresses tested, only H(2)O(2) was found to activate OMTK1. Out of four MAPKs, OMTK1 specifically activated MMK3 resulting in an increased cell death rate. Pull-down analysis between recombinant proteins indicated that OMTK1 directly interacts with MMK3 and that OMTK1 and MMK3 are part of a protein complex in vivo. These results indicate that OMTK1 plays a MAPK scaffolding role and functions in activation of H(2)O(2) -induced cell death in plants.
与其他真核生物一样，植物利用丝裂原活化蛋白激酶（MAPK）级联反应来介导对多种刺激的反应。与其他真核生物不同的是，植物拥有异常大量的MAPK组分，例如拟南芥中有20多种MAPK、10种MAPK激酶（MAPKK）和60种MAPKK激酶（MAPKKK）（MAPK Group (2002) Trends Plant Sci. 7, 301 - 308）。目前，植物中MAPK信号特异性是如何产生的大多仍不清楚。在此，我们从紫花苜蓿（Medicago sativa）中分离出了OMTK1（氧化应激激活的MAP三激酶1），一种新型的MAPKKK。在植物原生质体中，OMTK1表现出基础激酶活性，并被发现可诱导细胞死亡。在测试的一系列激素和胁迫中，仅发现H₂O₂能激活OMTK1。在四种MAPK中，OMTK1特异性激活MMK3，导致细胞死亡率增加。重组蛋白之间的下拉分析表明，OMTK1直接与MMK3相互作用，且OMTK1和MMK3是体内一种蛋白质复合物的组成部分。这些结果表明，OMTK1发挥MAPK支架作用，并在植物中H₂O₂诱导的细胞死亡激活过程中起作用。
