Mago Rohit, Tabe Linda, Vautrin Sonia, Šimková Hana, Kubaláková Marie, Upadhyaya Narayana, Berges Hélène, Kong Xiuying, Breen James, Doležel Jaroslav, Appels Rudi, Ellis Jeffrey G, Spielmeyer Wolfgang
BMC Plant Biol. 2014 Dec 30;14:379. doi: 10.1186/s12870-014-0379-z.
The adult plant stem rust resistance gene Sr2 was introgressed into hexaploid wheat cultivar (cv) Marquis from tetraploid emmer wheat cv Yaroslav, to generate stem rust resistant cv Hope in the 1920s. Subsequently, Sr2 has been widely deployed and has provided durable partial resistance to all known races of Puccinia graminis f. sp. tritici. This report describes the physical map of the Sr2-carrying region on the short arm of chromosome 3B of cv Hope and compares the Hope haplotype with non-Sr2 wheat cv Chinese Spring.
Sr2 was located to a region of 867 kb on chromosome 3B in Hope, which corresponded to a region of 567 kb in Chinese Spring. The Hope Sr2 region carried 34 putative genes but only 17 were annotated in the comparable region of Chinese Spring. The two haplotypes differed by extensive DNA sequence polymorphisms between flanking markers as well as by a major insertion/deletion event including ten Germin-Like Protein (GLP) genes in Hope that were absent in Chinese Spring. Haplotype analysis of a limited number of wheat genotypes of interest showed that all wheat genotypes carrying Sr2 possessed the GLP cluster; while, of those lacking Sr2, some, including Marquis, possessed the cluster, while some lacked it. Thus, this region represents a common presence-absence polymorphism in wheat, with presence of the cluster not correlated with presence of Sr2. Comparison of Hope and Marquis GLP genes on 3BS found no polymorphisms in the coding regions of the ten genes but several SNPs in the shared promoter of one divergently transcribed GLP gene pair and a single SNP downstream of the transcribed region of a second GLP.
Physical mapping and sequence comparison showed major haplotype divergence at the Sr2 locus between Hope and Chinese Spring. Candidate genes within the Sr2 region of Hope are being evaluated for the ability to confer stem rust resistance. Based on the detailed mapping and sequencing of the locus, we predict that Sr2 does not belong to the NB-LRR gene family and is not related to previously cloned, race non-specific rust resistance genes Lr34 and Yr36.
成株期抗秆锈病基因Sr2是从四倍体二粒小麦品种雅罗斯拉夫（cv Yaroslav）导入到六倍体小麦品种（cv）马奎斯中的，于20世纪20年代培育出抗秆锈病的品种霍普（cv Hope）。随后，Sr2被广泛应用，并对所有已知的小麦秆锈病菌生理小种都提供了持久的部分抗性。本报告描述了霍普品种3B染色体短臂上携带Sr2区域的物理图谱，并将霍普单倍型与不含Sr2的中国春小麦品种进行了比较。
在霍普中，Sr2定位在3B染色体上一个867 kb的区域，在中国春中对应一个567 kb的区域。霍普的Sr2区域含有34个推定基因，但在中国春的可比区域中只有17个被注释。这两个单倍型在侧翼标记之间存在广泛的DNA序列多态性，并且存在一个主要的插入/缺失事件，包括霍普中存在而中国春中缺失的10个类萌发素蛋白（GLP）基因。对少数感兴趣的小麦基因型进行单倍型分析表明，所有携带Sr2的小麦基因型都具有GLP基因簇；而在那些不携带Sr2的基因型中，一些（包括马奎斯）具有该基因簇，而一些则没有。因此，该区域代表了小麦中一种常见的存在/缺失多态性，基因簇的存在与Sr2的存在不相关。对3BS上霍普和马奎斯的GLP基因进行比较发现，10个基因的编码区没有多态性，但在一对反向转录的GLP基因的共享启动子中有几个单核苷酸多态性（SNP），在第二个GLP基因转录区域下游有一个SNP。
物理图谱绘制和序列比较显示，霍普和中国春在Sr2位点存在主要的单倍型差异。正在评估霍普Sr2区域内的候选基因赋予秆锈病抗性的能力。基于该位点的详细图谱绘制和测序，我们预测Sr2不属于NB-LRR基因家族，并且与先前克隆的、对小种非特异性的抗锈病基因Lr34和Yr36无关。
