A MAP Kinase Kinase Interacts with SymRK and Regulates Nodule Organogenesis in Lotus japonicus
A MAP Kinase Kinase Interacts with SymRK and Regulates Nodule Organogenesis in Lotus japonicus
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DOI：
10.1105/tpc.112.095984
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发表时间：
2012-02-01
期刊：
影响因子：
11.6
通讯作者：
Zhang, Zhongming
中科院分区：
文献类型：
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作者：
Chen, Tao;Zhu, Hui;Zhang, Zhongming
共生受体激酶SymRK是根瘤发育所必需的。一种与SymRK相互作用的蛋白（SIP2）在体外和植物体内都被发现能与SymRK形成蛋白复合物。SymRK和SIP2之间的相互作用在豆科植物中是保守的。SIP2基因在所检测的所有日本百脉根组织中都有表达。SIP2是一种典型的植物促分裂原活化蛋白激酶激酶（MAPKK），具有自磷酸化和转磷酸化活性。重组SIP2蛋白能够磷酸化酪蛋白和拟南芥MAP激酶MPK6。SymRK和SIP2不能相互作为磷酸化的底物。相反，当以MPK6为底物时，SymRK作为SIP2激酶的抑制剂，这表明SymRK可能作为SIP2信号通路的负调控因子。通过RNA干扰（RNAi）降低SIP2的表达导致转基因毛状根中形成的根瘤急剧减少。很大一部分SIP2 RNAi毛状根未能形成根瘤。在这些根中，SIP2以及感染线和根瘤原基形成的三个标记基因的表达水平急剧下调，而另外两个MAPKK基因的表达没有改变。这些观察结果表明SIP2在早期共生信号传导和根瘤器官发生中起着至关重要的作用。
The symbiosis receptor kinase, SymRK, is required for root nodule development. A SymRK-interacting protein (SIP2) was found to form protein complex with SymRK in vitro and in planta. The interaction between SymRK and SIP2 is conserved in legumes. The SIP2 gene was expressed in all Lotus japonicus tissues examined. SIP2 represents a typical plant mitogen-activated protein kinase kinase (MAPKK) and exhibited autophosphorylation and transphosphorylation activities. Recombinant SIP2 protein could phosphorylate casein and the Arabidopsis thaliana MAP kinase MPK6. SymRK and SIP2 could not use one another as a substrate for phosphorylation. Instead, SymRK acted as an inhibitor of SIP2 kinase when MPK6 was used as a substrate, suggesting that SymRK may serve as a negative regulator of the SIP2 signaling pathway. Knockdown expression of SIP2 via RNA interference (RNAi) resulted in drastic reduction of nodules formed in transgenic hairy roots. A significant portion of SIP2 RNAi hairy roots failed to form a nodule. In these roots, the expression levels of SIP2 and three marker genes for infection thread and nodule primordium formation were downregulated drastically, while the expression of two other MAPKK genes were not altered. These observations demonstrate an essential role of SIP2 in the early symbiosis signaling and nodule organogenesis.