Molecular Determinants Governing the Rice XA21/Xoo Interaction

受体激酶（RKs）在生物体感知和响应环境信号的机制中发挥重要作用，调节动物和植物的生长发育。本项目的长期目标是阐明植物RKs调控的信号转导级联。随着水稻抗病基因Xa21的克隆，水稻对水稻黄单胞菌具有抗性。oryzae(Xoo) (Song et al., 1995)，该实验室在阐明RK介导的植物抗病的分子基础方面处于有利地位。Xa21编码一个受体样激酶，该激酶携带一个假定的糖基化亮氨酸富重复（LRR）结构域、一个单通道跨膜结构域和一个丝氨酸苏氨酸激酶（STK结构域）。基于Xa21基因产物（Xa21）的序列和来自细菌和动物系统中受体激酶的信息，我们提出Xa21蛋白的LRR结构域位于细胞外并与配体相互作用。配体结合诱导蛋白质构象改变，激活胞内激酶结构域，触发下游防御反应，限制病原体生长。为了支持这一模型，已经证明激酶结构域能够进行自磷酸化，而LRR结构域足以进行种族特异性识别。本研究的具体目标是：1。2.确定XA21蛋白的亚细胞定位。克隆Xoo编码的无毒基因（avrXa21）。这些目标的实现不仅将导致确定水稻Xa21/avrXa21相互作用中抗病性的决定因素的特征，而且将扩大我们对植物中RK介导的信号转导的认识。从这些研究中获得的信息将有助于制定环境安全战略，以控制水稻和其他重要农学作物的疾病。

Receptor kinases (RKs) play an important role in the mechanism with which organisms perceive and respond to environmental signals, regulating growth and development in both animals and plants. The long-germ goal of this project is to elucidate the signal transduction cascade regulated by plant RKs. With the cloning of the rice disease resistance gene, Xa21, conferring resistance to Xanthomonas oryzae pv.oryzae(Xoo) (Song et al., 1995), this laboratory is in an excellent position to elucidate the molecular basis of RK mediated disease resistance in plants. Xa21 encodes a receptor-like kinase carrying a presumed glycosylated leucine rich repeat (LRR) domain, a single pass transmembrane domain, and a serine threonine kinase (STK domain). Based on the sequence of the Xa21 gene product (XA21) and information from receptor kinases in bacterial and animal systems, it is proposed that the LRR domain of the XA21 protein is extracellular and interacts with a ligand. Ligand binding induces a conformational change in the protein, activates the intracellular kinase domain, triggers a downstream defense response and restricts pathogen growth. In support of this model it has been demonstrated that the kinase domain is capable of autophosphorylation and that the LRR domain is sufficient for race-specific recognition. The specific objectives of this research are to: 1. Define the sub-cellular localization of the XA21 protein and 2. Clone the Xoo encoded avirulence gene (avrXa21). Accomplishment of these objectives will not only lead to the characterization of the determinants specifying disease resistance in the rice Xa21/avrXa21 interaction but will expand our knowledge of RK mediated signal transduction in plants. Information gained from these studies will facilitate the development of environmentally safe strategies for disease control in rice and other agronomically important crops.