The majority of plant disease resistance (R) genes encode proteins that share common structural features. However, the transcription activator-like effector (TALE)-associated executor type R genes show no considerable sequence homology to any known R genes. We adopted a map-based cloning approach and TALE-based technology to isolate and characterize Xa23, a new executor R gene derived from wild rice (Oryza rufipogon) that confers an extremely broad spectrum of resistance to bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo). Xa23 encodes a 113 amino acid protein that shares 50% identity with the known executor R protein XA10. The predicted transmembrane helices in XA23 also overlap with those of XA10. Unlike Xa10, however, Xa23 transcription is specifically activated by AvrXa23, a TALE present in all examined Xoo field isolates. Moreover, the susceptible xa23 allele has an identical open reading frame of Xa23 but differs in promoter region by lacking the TALE binding element (EBE) for AvrXa23. XA23 can trigger a strong hypersensitive response in rice, tobacco, and tomato. Our results provide the first evidence that plant genomes have an executor R gene family of which members execute their function and spectrum of disease resistance by recognizing the cognate TALEs in the pathogen.
大多數(shù)植物抗病基因編碼的蛋白質(zhì)具有共同的結(jié)構(gòu)特征。然而，類(lèi)轉(zhuǎn)錄激活因子效應(yīng)物（TALE）相關(guān)的執(zhí)行器型R基因與任何已知R基因沒(méi)有明顯的同源性。我們采用圖位克隆方法并基于TALE技術(shù)對(duì)Xa23基因進(jìn)行了分離鑒定，Xa23是一個(gè)來(lái)源于普通野生稻中的一個(gè)新的執(zhí)行器R基因，該基因?qū)Π兹~枯病菌(Xoo)引起的白葉枯病抗譜極廣。Xa23編碼一個(gè)含113個(gè)氨基酸殘基的蛋白質(zhì)，該蛋白質(zhì)具有與已知執(zhí)行器R蛋白XA10 50%的一致性。XA23中預(yù)測(cè)的跨膜螺旋結(jié)構(gòu)與XA10中的相同。然而，不同于Xa10，Xa23轉(zhuǎn)錄是通過(guò)AvrXa23特異誘導(dǎo)的，AvrXa23是存在于所有供試Xoo場(chǎng)地隔離群中的一個(gè)TALE。而且，敏感性的xa23等位基因具有與Xa23完全相同的開(kāi)放閱讀框，但不同的是在啟動(dòng)子區(qū)域缺少一個(gè)針對(duì)AvrXa23的TALE結(jié)合元件（EBE）。XA23能觸發(fā)水稻、煙草和番茄的強(qiáng)烈過(guò)敏反應(yīng)。我們的研究結(jié)果為植物基因組具有一個(gè)執(zhí)行器R基因家族提供第一個(gè)證據(jù)，其成員通過(guò)識(shí)別病原菌中同源TALEs來(lái)執(zhí)行它們的功能和廣譜抗病性。