Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is the most devastating bacterial disease of rice (Oryza sativa L.), a staple food crop that feeds half of the world’s population. In management of this disease, the most economical and effective approach is cultivating resistant varieties. Due to rapid change of pathogenicity in the pathogen, it is necessary to identify and characterize more host resistance genes for breeding new resistant varieties. We have previously identified the BB resistance (R) gene Xa23 that confers the broadest resistance to Xoo strains isolated from different rice-growing regions and preliminarily mapped the gene within a 1.7 cm region on the long arm of rice chromosome 11. Here, we report fine genetic mapping and in silico analysis of putative candidate genes of Xa23. Based on F2 mapping populations derived from crosses between Xa23-containing rice line CBB23 and susceptible varieties JG30 or IR24, six new STS markers Lj36, Lj46, Lj138, Lj74, A83B4, and Lj13 were developed. Linkage analysis revealed that the new markers were co-segregated with or closely linked to the Xa23 locus. Consequently, the Xa23 gene was mapped within a 0.4 cm region between markers Lj138 and A83B4, in which the co-segregating marker Lj74 was identified. The corresponding physical distance between Lj138 and A83B4 on Nipponbare genome is 49.8 kb. Six Xa23 candidate genes have been annotated, including four candidate genes encoding hypothetical proteins and the other two encoding a putative ADP-ribosylation factor protein and a putative PPR protein. These results will facilitate marker-assisted selection of Xa23 in rice breeding and molecular cloning of this valuable R gene.
白葉枯?。˙B）由水稻白葉枯黃單胞菌（Xoo）引起，對(duì)世界上一半左右人口主食的水稻是最具毀滅性的細(xì)菌性病害。對(duì)這種疾病的控制最經(jīng)濟(jì)和有效的方法就是培育抗性品種。由于病原菌致病性的快速變化，鑒定更多的宿主抗性基因?qū)ε嘤碌目共∑贩N非常必要。我們鑒定了BB抗性基因Xa23，該基因?qū)牟煌旧L(zhǎng)區(qū)域分離獲得的Xoo菌株具有光譜抗性，該基因被初定位于第11條染色體長(zhǎng)臂上1.7cM區(qū)域內(nèi)。本研究我們報(bào)道了精細(xì)遺傳圖譜，并對(duì)推定的候選基因Xa23進(jìn)行了計(jì)算機(jī)模擬分析。基于攜帶Xa23水稻株系CBB23與感性品種JG30或IR24雜交所構(gòu)建的F2作圖群體，開發(fā)了6個(gè)新的STS標(biāo)記Lj36、Lj46、Lj138、Lj74、A83B4和Lj13。連鎖分析表明新標(biāo)記與Xa23位點(diǎn)共分離或緊密連鎖。結(jié)果，Xa23基因被定位于標(biāo)記Lj138和A83B4之間0.4cM的區(qū)域內(nèi)，并鑒定該基因在該區(qū)域與標(biāo)記Lj74共分離。在日本晴基因組中，與Lj138和A83B4之間區(qū)域相對(duì)應(yīng)的物理距離為49.8kb。6個(gè)Xa23候選基因被注釋，包括4個(gè)編碼假定蛋白的基因和其他2個(gè)編碼推定ADP-核糖基化因子蛋白以及1個(gè)推定PPR蛋白。這些研究結(jié)果將有利于在水稻育種中對(duì)Xa23進(jìn)行分子標(biāo)記選擇，以及對(duì)有價(jià)值的抗性基因進(jìn)行分子克隆。