Tan Shengjun, Wang Dan, Ding Jing, Tian Dacheng, Zhang Xiaohui, Yang Sihai
State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, China.
Genetica. 2011 Dec;139(11-12):1465-75. doi: 10.1007/s10709-012-9645-x. Epub 2012 Mar 27.
The XA21 protein has broad spectrum resistance against Xanthomonas oryzae pv. oryzae. Although Xa21-mediated immunity is well characterized, little is known about the origin and evolutionary history of this gene in grasses. Therefore, we analyzed all Xa21 gene homologs in eight whole-genome sequenced rice lines, as well as in four gramineous genomes, rice, Brachypodium, sorghum and maize; using Arabidopsis Xa21 homologs as outgroups, 17, 7, 7 and 3 Xa21 homologs were detected in these four grasses, respectively. Synteny and phylogenetic analysis showed that frequent gene translocation, duplication and/or loss, have occurred at Xa21 homologous loci, suggesting that they have undergone or are undergoing rapid generation of copy number variations. Within the rice species, the high level of nucleotide diversity between Xa21-like orthologs showed a strong association with the presence/absence haplotypes, suggesting that the genetic structure of rice lines plays an important role in the variations between these Xa21-like orthologs. Strongly positive selection was detected in the core region of the leucine-rich repeat domains of the Xa21 subclade among the rice lines, indicating that the rapid gene diversification of Xa21 homologs may be a strategy for a given species to adapt to the changing spectrum of species-specific pathogens.
XA21蛋白对水稻白叶枯病菌具有广谱抗性。尽管Xa21介导的免疫反应已得到充分表征，但对于该基因在禾本科植物中的起源和进化历史却知之甚少。因此，我们分析了8个全基因组测序水稻品系以及水稻、短柄草、高粱和玉米这4个禾本科基因组中的所有Xa21基因同源物；以拟南芥Xa21同源物作为外类群，在这4种禾本科植物中分别检测到17个、7个、7个和3个Xa21同源物。共线性和系统发育分析表明，Xa21同源位点发生了频繁的基因易位、复制和/或丢失，这表明它们已经经历或正在经历拷贝数变异的快速产生。在水稻物种内，Xa21样直系同源物之间高水平的核苷酸多样性与存在/缺失单倍型密切相关，这表明水稻品系的遗传结构在这些Xa21样直系同源物之间的变异中起着重要作用。在水稻品系中，Xa21亚分支富含亮氨酸重复结构域的核心区域检测到强烈的正选择，这表明Xa21同源物的快速基因多样化可能是特定物种适应物种特异性病原体不断变化的谱系的一种策略。
