Kinase mediated signaling in the rice defense response

描述(申请人提供)：细胞表面受体对细胞外信号的感知对真核发育和免疫至关重要。这些受体中的许多在其胞浆区(RKS)具有内在的蛋白激酶活性，并通过磷酸化和去磷酸化事件来调节靶基因的转录。调节异常可导致多种疾病，因此了解RK的特异性和功能是如何控制的是重要的。 与大多数蛋白激酶通过激活片段的磷酸化来调节不同，激活片段是一个位于中心位置的环，靠近催化中心，对于一些RK来说，一个新的主题是膜旁(JM)结构域在它们的激活中发挥关键的调节作用。在这种情况下，JM结构域中的残基既有积极的调节功能，也有消极的调节功能。在非磷酸化状态下，它们抑制催化活性，一旦磷酸化，它们就成为下游信号蛋白的高亲和力结合部位。到目前为止，通过JM结构域调节RK信号是只有少数控制重要细胞过程的受体家族所特有的，因此人们对探索这种控制的分子基础非常感兴趣。 水稻Xa21基因在胞外区编码一个富含亮氨酸重复序列(LRRs)的RK，是天然免疫应答中的关键识别和信号决定因素，天然免疫应答是植物和动物之间广泛保守的病原体防御途径。XA21在激活段不是自动磷酸化的，至少有四个XA21结合蛋白(XB)需要JM区的磷酸化残基才能相互作用。这些基因包括Xb10和Xb15，Xb10编码一个假定的转录调节因子，Xb15编码一个PP2c磷酸酶样蛋白。 根据这些结果，我们推测Xa21 JM结构域在XA21激酶介导的信号转导中起关键作用，JM结合蛋白作为正性或负性调节因子控制防御相关基因的转录。为了进一步检验这一假设，我们建议： 1.确定Xb10和Xb15在XA2‘L介导和鞭毛蛋白激活的防御反应中的作用。 2.进一步鉴定XA21 JM结构域，鉴定XA21与XA21相互作用的结构域，并评估XA21依赖的磷酸化作用 3.研究XA2jl和XBS的细胞相互作用，并在体内鉴定新的复合体成分。

DESCRIPTION (provided by applicant): Perception of extracellular signals by cell surface receptors is of central importance to eukaryotic development and immunity. Many of these receptors possess intrinsic protein kinase activity in their cytoplasmic domains (RKs) and regulate transcription of target genes through phosphorylation and dephosphorylation events. Abnormal regulation can lead to a variety of diseases and it is therefore important to understand how RK specificity and function are controlled. In contrast to most protein kinases that are regulated by phosphorylation of the activation segment, a centrally located loop that sits close to the catalytic center, an emerging theme for some RKs is that the juxtamembrane (JM) domain plays a key regulatory role in their activation. In this case, residues in the JM domain perform both positive and negative regulatory functions. In their unphosphorylated state they repress catalytic activity and upon phosphorylation they serve as high affinity binding sites for downstream signaling proteins. Regulation of RK signaling through the JM domain is so far unique to only a few receptor families controlling important cellular processes and consequently there is great interest in exploring the molecular basis for this control. The rice XA21 gene, encoding a RK with leucine rich repeats (LRRs) in the extracellular domain, is a key recognition and signaling determinant in the innate immune response, a pathogen defense pathway widely conserved between plants and animals. XA21 is not autophosphorylated in the activation segment and at least four XA21 binding proteins (Xbs) require phosphorylated residues in the JM region for interaction. These include Xb10, encoding a putative transcriptional regulator and Xb15 encoding a PP2c phosphatase-like protein. Based on these results we hypothesize that the XA21 JM domain plays a key role in XA21 kinase-mediated signal transduction and that JM-binding protein's act as positive or negative regulators to control transcription of defense related genes. To further test this hypothesis we propose to: 1. Determine the role of Xb10 and Xb15 in Xa2'l -mediated and flagellin-activated defense responses. 2. Further characterize the XA21 JM domain, identify Xb kinase interaction domains and assess the role of XA21-dependent phosphorylation 3. Characterize the cellular interactions of XA2jl and Xbs and identify new components in the in vivo complexes.