MOLECULAR GENETIC ANALYSIS OF RICE DISEASE RESISTANCE

许多植物病原体相互作用的遗传分析表明， 抗性植物通常含有单一的基因座， 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，该假说指出， 抗病性由一个显性抗性位点控制， 编码一种（或多种）特异性相互作用的产物（直接或间接） 与相应的无毒基因的产物。 阐明 由这些基因座编码的基因产物的功能已被 没有克隆基因。 在水稻白叶枯病中， 寄主水稻（Oryza sativa）和病原菌野油菜黄单胞菌（Xanthomonascampestris pv.）Xco） 都可以应用于分子遗传学，这使得它成为一个有吸引力的系统， 抗病性的研究。 只有一个基因座Xa 21赋予对 Xco的所有种族。 基因对基因假说预测Xco菌株 含有单一基因座avrXa 21，其赋予病原体无毒力。 本建议的具体目标是：1）建设一个高 植物抗性位点Xa 21的解析遗传图谱; 2）鉴定 并分析了Xa 21水稻品系的突变体， 3）构建Xa 21基因组区域的物理图谱 分离含有Xa 21的重叠酵母人工染色体克隆; 4)克隆和表征Xa 21基因; 5）鉴定化学和生物学特性; 转座子诱导的Xco突变体可在Xa 21植物上引起疾病; 5）通过突变体的互补，T克隆avrXa 21无毒基因 表型。 宿主和病原体基因的分子特征， 抗病性将有助于回答有关复杂性的问题， 抗性位点Xa 21。 Xa 21和avrXa 21的克隆将代表 第一次发现抗病基因和相应的 无毒基因已从任何作物中分离出来。 分析基因 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，以及 基因表达。 最后，克隆基因提高了 通过基因改造， 转移实验

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.