Key Laboratory of Horticulture Biology, Ministry of Education, and Department of Vegetable Crops, College of Horticulture and Forestry, Huazhong Agricultural University, Wuhan, China.
Mol Biol Evol. 2011 Jan;28(1):313-25. doi: 10.1093/molbev/msq216. Epub 2010 Aug 16.
Disease-resistance genes (R-genes) in plants show complex evolutionary patterns. We investigated the evolution of the Rp1 R-gene family in Poaceae, and 409 Rp1 fragments were sequenced from 21 species. Our data showed that the common ancestor of Poaceae had two Rp1 loci, but the number of Rp1 locus in extant species varies from one to five. Some wheat and Zea genotypes have dozens of Rp1 homologues in striking contrast to one or two copies in Brachypodium distachyon. The large number of diverse Rp1 homologues in Zea was the result of duplications followed by extensive sequence exchanges among paralogues, and all genes in maize have evolved in a pattern of Type I R-genes. The high frequency of sequence exchanges did not cause concerted evolution in Zea species, but concerted evolution was obvious between Rp1 homologues from genera Zea and Sorghum. Differentiation of Type I and Type II Rp1 homologues was observed in Oryza species, likely occurred in their common ancestor. One member (Type II R-gene) in the Oryza Rp1 cluster did not change sequences with its paralogues, whereas the other paralogues (Type I R-genes) had frequent sequence exchanges. The functional Pi37 resistance gene in rice was generated through an unequal crossover between two neighboring paralogues followed by four point mutations. The Rp1 homologues in wheat and barley were most divergent, probably due to lack of sequence exchanges among them. Our results shed more light on R-gene evolution, particularly on the differentiation of Type I and Type II R-genes.
植物中的抗病基因（R 基因）表现出复杂的进化模式。我们研究了禾本科植物 Rp1 基因家族的进化，从 21 个物种中测序了 409 个 Rp1 片段。我们的数据表明，禾本科植物的共同祖先有两个 Rp1 基因座，但现存物种的 Rp1 基因座数量从一个到五个不等。一些小麦和玉米基因型有数十个 Rp1 同源物，与拟南芥中的一个或两个拷贝形成鲜明对比。玉米中大量不同的 Rp1 同源物是复制的结果，随后在旁系同源物之间发生了广泛的序列交换，并且玉米中的所有基因都以 I 型 R 基因的模式进化。大量的序列交换并没有导致玉米物种的协同进化，但玉米和高粱属 Rp1 同源物之间的协同进化是明显的。在水稻物种中观察到 I 型和 II 型 Rp1 同源物的分化，可能发生在它们的共同祖先中。水稻 Rp1 基因座中的一个成员（II 型 R 基因）与其旁系同源物没有改变序列，而其他旁系同源物（I 型 R 基因）则发生了频繁的序列交换。水稻中 Pi37 抗性基因的功能是通过两个相邻旁系同源物之间的不等交换和四个点突变产生的。小麦和大麦中的 Rp1 同源物差异最大，可能是由于它们之间缺乏序列交换。我们的研究结果为 R 基因进化提供了更多的信息，特别是 I 型和 II 型 R 基因的分化。
