Kalavacharia V, Stavely J R, Myers J R, McClean P E
Department of Plant Sciences, North Dakota State University, Fargo 58105, USA.
Mol Plant Microbe Interact. 2000 Nov;13(11):1237-42. doi: 10.1094/MPMI.2000.13.11.1237.
Race-specific resistance to the bean rust pathogen (Uromyces appendiculatus) is provided by a number of loci in common bean (Phaseolus vulgaris). The Ur-3 locus controls hypersensitive resistance (HR) to 44 of the 89 races curated in the United States. To better understand resistance mediated by this locus, we developed new genetic material for analysis. We developed a population of mutagenized seed of cv. Sierra (genotype = Ur-3 ur-4 ur-6) that was screened with a bean rust race that is normally incompatible (HR response) on Ur-3 genotypes. We discovered two mutants of common bean, crg and ur3-delta3, in which uredinia formed on leaves (a compatible interaction) following infection. The F1 generation from a cross of these two mutants expressed the HR response, and the F2 generation segregated in a ratio of 9:7 (HR/uredinia formation). Therefore, the two genes are unlinked. Further genetic analysis determined that the mutation in ur3-delta3 was in the Ur-3 locus, and the mutation in crg was in a newly discovered gene given the symbol Crg (Complements resistance gene). Each mutation was inherited in a recessive manner. Unlike ur3-delta3, crg expressed reduced compatibility to bean rust races 49 and 47 that are normally fully compatible on genotypes, such as Sierra, that are homozygous recessive at the Ur-4 and Ur-6 loci. This suggests a gene mutated in crg is normally a positive compatibility factor for the bean-bean rust interaction. Polymerase chain reaction analysis of crg with primers to common bean resistance gene analogs (RGA) that contain a nucleotide-binding site sequence similar to those found in a number of plant disease resistance genes revealed that crg is missing the SB1 RGA, but not the linked SB3 and SB5 RGAs. Genetic analyses revealed that Crg cosegregates with the SB1 RGA. These results demonstrate that Crg is located near a RGA cluster in the common bean genome.
菜豆（Phaseolus vulgaris）中的多个基因座提供了对菜豆锈病病原体（Uromyces appendiculatus）的种族特异性抗性。Ur-3基因座控制对美国收集的89个小种中44个小种的过敏反应抗性（HR）。为了更好地理解该基因座介导的抗性，我们开发了用于分析的新遗传材料。我们开发了一个cv. Sierra（基因型=Ur-3 ur-4 ur-6）诱变种子群体，用一种在Ur-3基因型上通常不亲和（HR反应）的菜豆锈病小种进行筛选。我们发现了两个菜豆突变体，crg和ur3-delta3，感染后叶片上形成了夏孢子堆（一种亲和互作）。这两个突变体杂交的F1代表现出HR反应，F2代以9:7（HR/夏孢子堆形成）的比例分离。因此，这两个基因不连锁。进一步的遗传分析确定ur3-delta3中的突变位于Ur-3基因座，crg中的突变位于一个新发现的基因，命名为Crg（互补抗性基因）。每个突变均以隐性方式遗传。与ur3-delta3不同，crg对菜豆锈病小种49和47的亲和性降低，这两个小种在诸如Sierra等在Ur-4和Ur-6基因座纯合隐性的基因型上通常完全亲和。这表明crg中突变的基因通常是菜豆与菜豆锈病互作的正亲和因子。用与菜豆抗性基因类似物（RGA）的引物对crg进行聚合酶链反应分析，这些引物含有与许多植物抗病基因中发现的核苷酸结合位点序列相似的序列，结果显示crg缺失SB1 RGA，但不缺失连锁的SB3和SB5 RGA。遗传分析表明Crg与SB1 RGA共分离。这些结果证明Crg位于菜豆基因组中的一个RGA簇附近。
