MOLECULAR GENETIC ANALYSIS OF RICE DISEASE RESISTANCE

对许多植物病原菌相互作用的遗传分析表明 抗性植物通常含有指定抗性的单个基因座。 含有互补无毒基因的病原体。这种遗传模式 是“基因对基因”假说的基础，该假说认为植物 抗病是由单个显性抗病基因座控制的 对特定交互的产品(S)进行编码(直接或间接) 以及相应无毒基因的产物。澄清： 由这些基因座编码的基因产物的功能受到 没有克隆的基因。在水稻白叶枯病中， 寄主(Oryza Sativa)和病原(Xanthomonas campestris PV.Oryzae，XCO) 是服从分子遗传学的，这使得这一系统对 抗病研究。只有一个基因座，Xa21，对 XCO的所有种族。基因对基因假说预测XCO菌株 含有一个单一的基因座avrXa21，它赋予病原体无毒。 该方案的具体目标是：1)建设一个高层次的 植物抗病基因座Xa21的分辨率遗传图谱；2)鉴定 并分析了水稻Xa21品系的易感突变 XCO感染；3)构建Xa21基因组区域物理图谱 分离出含Xa21的重叠酵母人工染色体克隆； 4)克隆和鉴定Xa21基因(S)；5)对Xa21基因进行化学和分子生物学鉴定 转座子诱导的XCO突变体可在Xa21植株上致病； 5)通过对突变体的互补克隆avrXa21无毒基因 表型。 指定寄主和病原体基因的分子特征 抗病能力将有助于回答有关病毒复杂性的问题 抗性基因座Xa21。Xa21和avrXa21的克隆将代表 第一次既有抗病基因又有相应的 已从任何作物中分离出无毒基因。基因分析 由这些基因座编码的产物将有助于对 信号转导途径，蛋白质-蛋白质相互作用和调控 基因表达。最后，克隆基因增加了 利用基因技术拓展其他作物抗病种质资源 传递实验。

Genetic analysis of many plant pathogen interactions has demonstrated that resistant plants often contain single loci that specify resistance against pathogens containing complementary avirulence genes. This genetic pattern is the basis of the "gene-for-gene" hypothesis which states that plant disease resistance is controlled by a single dominant resistance locus that encodes a product(s) that specifically interacts (directly or indirectly) with the product of a corresponding avirulence gene. Elucidation of the function of the gene products encoded by these loci has been impeded by the absence of cloned genes. In the bacterial blight disease of rice, both the host (Oryza sativa) and pathogen (Xanthomonas campestris pv. oryzae, Xco) are amenable to molecular genetics, making this an attractive system for studies of disease resistance. Only one locus, Xa21, confers resistance to all races of Xco. The gene-for-gene hypothesis predicts that Xco strains contain a single locus, avrXa21, that confers avirulence to the pathogen. The specific objectives of this proposal are: 1) To construct a high resolution genetic map of the plant resistance locus Xa21; 2) To identify and analyze mutants of the Xa21 line of rice that are susceptible to infection by Xco; 3) To construct a physical map of the Xa21 genomic region and isolate overlapping yeast artificial chromosome clones containing Xa21; 4) To clone and characterize the Xa21 gene(s); 5) To identify chemical and transposon induced mutants of Xco that can cause disease on Xa21 plants; and 5) T clone the avrXa21 avirulence gene by complementation of the mutant phenotype. Molecular characterization of the host and pathogen genes that specify disease resistance will help answer questions regarding the complexity of the resistance locus Xa21. Cloning of Xa21 and avrXa21 would represent the first time that both a disease resistance gene and the corresponding avirulence gene have been isolated from any crop. Analysis of the gene products encoded by these loci will contribute to a basic understanding of signal transduction pathways, protein-protein interactions, and control of gene expression. Finally, having the gene cloned raises the possibility of expanding the resistant germplasm of other crop species through gene transfer experiments.