Shan Weixing, Cao Minh, Leung Dan, Tyler Brett M
Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
Mol Plant Microbe Interact. 2004 Apr;17(4):394-403. doi: 10.1094/MPMI.2004.17.4.394.
We have used map-based approaches to clone a locus containing two genes, Avr1b-1 and Avr1b-2, required for avirulence of the oomycete pathogen Phytophthora sojae (Kaufmann & Gerdemann) on soybean plants carrying resistance gene Rps1b. Avr1b-1 was localized to a single 60-kb bacterial artificial chromosome (BAC) clone by fine-structure genetic mapping. Avr1b-1 was localized within the 60-kb region by identification of an mRNA that is expressed in a race-specific and infection-specific manner and that encodes a small secreted protein. When the Avr1b-1 protein was synthesized in the yeast Pichia pastoris and the secreted protein infiltrated into soybean leaves, it triggered a hypersensitive response specifically in host plants carrying the Rps1b resistance gene. This response eventually spread to the entire inoculated plant. In some isolates of P. sojae virulent on Rps1b-containing cultivars, such as P7081 (race 25) and P7076 (race 19), the Avr1b-1 gene had numerous substitution mutations indicative of strong divergent selection. In other isolates, such as P6497 (race 2) and P9073 (race 25), there were no substitutions in Avr1b-1, but Avr1b-1 mRNA did not accumulate. Genetic complementation experiments with P6497 revealed the presence of a second gene, Avr1b-2, required for the accumulation of Avr1b-1 mRNA. Avr1b-2 was genetically mapped to the same BAC contig as Avr1b-1, using a cross between P7064 (race 7) and P6497. The Avr1k gene, required for avirulence on soybean cultivars containing Rps1k, was mapped to the same interval as Avr1b-1.
我们采用基于图谱的方法克隆了一个包含两个基因Avr1b - 1和Avr1b - 2的位点，这两个基因是卵菌病原体大豆疫霉（考夫曼和格德曼）对携带抗性基因Rps1b的大豆植株无毒力所必需的。通过精细结构遗传图谱分析，Avr1b - 1被定位到一个单一的60 kb细菌人工染色体（BAC）克隆上。通过鉴定一种以小种特异性和感染特异性方式表达且编码一种小分泌蛋白的mRNA，Avr1b - 1被定位在60 kb区域内。当Avr1b - 1蛋白在毕赤酵母中合成且分泌蛋白渗入大豆叶片时，它在携带Rps1b抗性基因的寄主植物中特异性引发过敏反应。这种反应最终蔓延到整个接种的植株。在一些对含Rps1b品种有毒力的大豆疫霉菌株中，如P7081（小种25）和P7076（小种19），Avr1b - 1基因有许多替代突变，表明存在强烈的趋异选择。在其他菌株中，如P6497（小种2）和P9073（小种25），Avr1b - 1没有替代突变，但Avr1b - 1 mRNA不积累。用P6497进行的遗传互补实验揭示了存在第二个基因Avr1b - 2，它是Avr1b - 1 mRNA积累所必需的。利用P7064（小种7）和P6497之间的杂交，Avr1b - 2被遗传定位到与Avr1b - 1相同的BAC重叠群上。在含Rps1k的大豆品种上无毒力所必需的Avr1k基因被定位到与Avr1b - 1相同的区间。
