Xu Juan, Li Yuan, Wang Ying, Liu Hongxia, Lei Lei, Yang Hailian, Liu Guoqin, Ren Dongtao
State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100094, China.
J Biol Chem. 2008 Oct 3;283(40):26996-7006. doi: 10.1074/jbc.M801392200. Epub 2008 Aug 7.
Mitogen-activated protein kinase (MAPK) cascades play important roles in regulating plant growth, development, and responses to various environmental stimuli. We demonstrate that MKK9, an MKK, is an upstream activator of the MPKs MPK3 and MPK6 both in vitro and in planta. Expression of active MKK9 protein in transgenic plants induces the synthesis of ethylene and camalexin through the activation of the endogenous MPK3 and MPK6 kinases. As a consequence, transcription of multiple genes responsible for ethylene biosynthesis, ethylene responses, and camalexin biosynthesis is coordinately up-regulated. The activation of MKK9 inhibits hypocotyl elongation in the etiolated seedlings. MKK9-mediated effects on hypocotyl elongation were blocked by the ethylene biosynthesis inhibitor, aminoethoxyvinylglycine, and ethylene receptor antagonist, Ag(+). Expression of active MKK9 protein enhances the sensitivity of transgenic seedlings to salt stress, whereas loss of MKK9 activity reduces salt sensitivity indicating a role for MKK9 in the salt stress response. The results reported here reveal that the MKK9-MPK3/MPK6 cascade participates in the regulation of the biosynthesis of ethylene and camalexin and may be an important axis in the stress responses of Arabidopsis.
丝裂原活化蛋白激酶（MAPK）级联在调节植物生长、发育以及对各种环境刺激的反应中发挥着重要作用。我们证明，MKK9（一种MKK）在体外和植物体内都是MPK3和MPK6的上游激活剂。在转基因植物中表达活性MKK9蛋白通过激活内源性MPK3和MPK6激酶诱导乙烯和camalexin的合成。因此，负责乙烯生物合成、乙烯反应和camalexin生物合成的多个基因的转录被协同上调。MKK9的激活抑制了黄化幼苗下胚轴的伸长。乙烯生物合成抑制剂氨基乙氧基乙烯基甘氨酸和乙烯受体拮抗剂Ag(+)阻断了MKK9介导的对下胚轴伸长的影响。活性MKK9蛋白的表达增强了转基因幼苗对盐胁迫的敏感性，而MKK9活性的丧失降低了盐敏感性，表明MKK9在盐胁迫反应中发挥作用。此处报道的结果表明，MKK9-MPK3/MPK6级联参与乙烯和camalexin生物合成的调节，可能是拟南芥应激反应中的一个重要轴。
