Yahiaoui Nabila, Brunner Susanne, Keller Beat
Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, 8008 Zürich, Switzerland.
Plant J. 2006 Jul;47(1):85-98. doi: 10.1111/j.1365-313X.2006.02772.x. Epub 2006 Jun 1.
Plant defence against pathogens is controlled by disease resistance (R) gene products that directly or indirectly detect specific pathogen effectors. Plant-pathogen interactions have been proposed to follow a co-evolutionary arms-race model where R genes are recent and evolve rapidly in response to structural changes in matching pathogen effectors. However, the longevity and extensive polymorphism of R genes studied were more consistent with balancing selection maintaining ancient and diverse R genes or alleles. In bread wheat (Triticum aestivum), the Pm3 locus confers race-specific resistance to wheat powdery mildew (Blumeria graminis f.sp. triticii). Here we describe recently generated Pm3 resistance alleles that all derive from one susceptible allele, Pm3CS, which is widespread among hexaploid bread-wheat lines. One group of four Pm3 resistance alleles shows few, clearly delimited, polymorphic sequence blocks of ancient origin, embedded in sequences identical to Pm3CS and possibly derived from gene conversion. A second group of three alleles differs from Pm3CS by only two to five mutations, all non-synonymous, and all in the leucine-rich repeat-encoding region. Transient transformation experiments confirmed that Pm3 resistance specificities are based on one or few amino acid changes. The Pm3CS allele was found in wild tetraploid wheat, the ancestor of hexaploid bread wheat, specifically from southern Turkey, a region proposed to be the site of wheat domestication. Based on these data, we propose that the Pm3 resistance alleles were generated in agricultural ecosystems after domestication of wheat 10,000 years ago. The evolution of Pm3 alleles in wheat is best described by the model of evolved recycling, where novel genetic variation is integrated in plant populations together with recycling of old variation.
植物对病原体的防御由抗病（R）基因产物控制，这些产物直接或间接检测特定的病原体效应子。植物与病原体的相互作用被认为遵循一种共同进化的军备竞赛模型，其中R基因是新近出现的，并随着匹配病原体效应子的结构变化而迅速进化。然而，所研究的R基因的长寿性和广泛多态性更符合平衡选择维持古老且多样的R基因或等位基因的情况。在面包小麦（普通小麦）中，Pm3位点赋予对小麦白粉病（禾本科布氏白粉菌小麦专化型）的小种特异性抗性。在这里，我们描述了最近产生的Pm3抗性等位基因，它们都源自一个易感等位基因Pm3CS，该等位基因在六倍体面包小麦品系中广泛存在。一组四个Pm3抗性等位基因显示出很少的、明确界定的、起源古老的多态性序列块，这些序列块嵌入与Pm3CS相同的序列中，可能源自基因转换。另一组三个等位基因与Pm3CS的差异仅在于两到五个突变，所有这些突变都是非同义的，并且都位于富含亮氨酸重复序列编码区域。瞬时转化实验证实，Pm3抗性特异性基于一个或几个氨基酸变化。在野生四倍体小麦中发现了Pm3CS等位基因，野生四倍体小麦是六倍体面包小麦的祖先，具体来自土耳其南部，该地区被认为是小麦驯化的地点。基于这些数据，我们提出Pm3抗性等位基因是在一万年前小麦驯化后的农业生态系统中产生的。小麦中Pm3等位基因的进化最好用进化循环模型来描述，即新的遗传变异与旧变异的循环一起整合到植物群体中。
