Agrobacterium transient expression system as a tool for the isolation of disease resistance genes:: application to the Rx2 locus in potato
Agrobacterium transient expression system as a tool for the isolation of disease resistance genes:: application to the Rx2 locus in potato
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DOI：
10.1046/j.1365-313x.2000.00654.x
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发表时间：
2000-01-01
期刊：
影响因子：
7.2
通讯作者：
Baulcombe, DC
中科院分区：
文献类型：
--
作者：
Bendahmane, A;Querci, M;Baulcombe, DC
Rx 2赋予对马铃薯病毒X（PVX）的抗性。为了克隆Rx 2，我们开发了一个系统的基础上，农杆菌介导的瞬时表达的候选R基因在转基因烟草叶片表达的PVX外壳蛋白激发子Rx 2介导的抗性。利用该系统，鉴定了在诱导子存在下特异性地诱导HR的马铃薯基因。根据遗传学和功能分析，确定所克隆的基因为Rx 2。该瞬时表达系统具有克隆其它抗性基因的潜力。Rx 2基因位于马铃薯V染色体上，编码的蛋白质与马铃薯XII染色体上编码的Rx 1和Rxh 1的产物高度相似。Rxh 1已在其他地方显示编码马铃薯孢囊线虫抗性基因Gpa 2。所有三种蛋白质都是在亮氨酸拉链-核苷酸结合位点-富含亮氨酸的重复类抗性基因产物中。Rx 1和Rx 2在功能上相同，并且在C末端区域几乎相同，这与富含亮氨酸的重复序列在识别PVX外壳蛋白中的作用一致。在N端，一半有一些区域，其中Rx 1和Rx 2蛋白彼此比Rxh 1蛋白更相似。然而，在其他区域，这些蛋白质与Rxh 1的相似性比彼此更大。基于这种序列相似性的镶嵌模式，我们得出结论，通过基因转换的过程，在遗传上不连锁的抗病基因之间重复发生序列交换。
Rx2 confers resistance against potato virus X (PVX). To clone Rx2, we developed a system based on Agrobacterium-mediated transient expression of candidate R genes in transgenic tobacco leaves expressing the PVX coat protein elicitor of Rx2-mediated resistance. Using this system, a potato gene eliciting HR specifically in the presence of the elicitor was identified. Based on genetical and functional analysis, it is concluded that the cloned gene is Rx2. The transient expression system is potentially adaptable to cloning of any other resistance gene. The Rx2 locus is on chromosome V of potato and the encoded protein is highly similar to the products of Rx1 and Rxh1 encoded on potato chromosome XII. Rxh1 has been shown elsewhere to encode a potato cyst nematode resistance gene Gpa2. All three proteins are in the leucine zipper-nucleotide binding site-leucine rich repeat class of resistance gene products. Rx1 and Rx2 are functionally identical and are almost identical in the C terminal region consistent with a role of the leucine rich repeats in recognition of the PVX coat protein. In the N terminal, half there are some regions where the Rx1 and Rx2 proteins are more similar to each other than to the Rxh1 protein. However, in other regions these proteins are more similar to Rxh1 than to each other. Based on this mosaic pattern of sequence similarity, we conclude that sequence exchange occurs repeatedly between genetically unlinked disease resistance genes through a process of gene conversion.