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着重要作用，调节动植物的生长发育。这个项目的长期目标是阐明受植物RKS调控的信号转导级联。随着水稻抗病基因Xa21的克隆(Song等人，1995)，本实验室为阐明RK介导的植物抗病的分子基础奠定了基础。XA21编码一个受体样激酶，携带一个糖基化的富含亮氨酸重复序列(LRR)结构域、一个单通跨膜结构域和一个丝氨酸苏氨酸激酶(STK结构域)。根据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，认为XA21蛋白的LRR结构域是细胞外的，并与配体相互作用。配体结合诱导蛋白质的构象变化，激活细胞内的激酶域，触发下游防御反应，限制病原体的生长。为了支持这一模型，已经证明了激酶结构域能够自动磷酸化，并且LRR结构域足以进行种族特异性识别。本研究的具体目的是：1.确定Xa21蛋白的亚细胞定位；2.克隆Xoo编码的无毒基因(AvrXa21)。这些目标的实现不仅将导致鉴定水稻Xa21/avrXa21相互作用中决定抗病的决定因素，而且将扩大我们对RK介导的植物信号转导的了解。从这些研究中获得的信息将有助于制定对环境无害的水稻和其他重要农艺作物的疾病控制战略。

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.