Bacterial blight (BB) is a globally devastating rice disease caused by Xanthomonas oryzae pv. oryzae (Xoo). The use of disease resistance (R) genes in rice breeding is an effective and economical strategy for the control of this disease. Nevertheless, a majority of R genes lack durable resistance for long-term use under global warming conditions. Here, we report the isolation of a novel executor R gene, Xa7, that confers extremely durable, broad-spectrum, and heat-tolerant resistance to Xoo. The expression of Xa7 was induced by incompatible Xoo strains that secreted the transcription activator-like effector (TALE) AvrXa7 or PthXo3, which recognized effector binding elements (EBEs) in the Xa7 promoter. Furthermore, Xa7 induction was faster and stronger under high temperatures. Overexpression of Xa7 or co-transformation of Xa7 with avrXa7 triggered a hypersensitive response in plants. Constitutive expression of Xa7 activated a defense response in the absence of Xoo but inhibited the growth of transgenic rice plants. In addition, analysis of over 3000 rice varieties showed that the Xa7 locus was found primarily in the indica and aus subgroups. A variation consisting of an 11-bp insertion and a base substitution (G to T) was found in EBEAvrXa7 in the tested varieties, resulting in a loss of Xa7 BB resistance. Through a decade of effort, we have identified an important BB resistance gene and characterized its distinctive interaction with Xoo strains; these findings will greatly facilitate research on the molecular mechanism of Xa7-mediated resistance and promote the use of this valuable gene in breeding.
白葉枯病是由水稻黃單胞菌(Xoo)引起的一種全球性毀滅性病害。在水稻育種中利用抗病R基因是防治該病的一種經(jīng)濟(jì)有效的策略。然而，大多數(shù)R基因缺乏持久的抵抗力，無(wú)法在全球變暖條件下長(zhǎng)期使用。本文我們報(bào)道了一個(gè)新的R基因Xa7，該基因?qū)?em>Xoo具有非常持久和廣譜的抗性，且耐熱。Xa7的表達(dá)受Xoo不親和菌株誘導(dǎo)，后者能分泌轉(zhuǎn)錄激活因子樣效應(yīng)子（TALE）AvrXa7或PthXo3，能識(shí)別Xa7啟動(dòng)子中的效應(yīng)子結(jié)合元件（EBEs）。高溫下，Xa7的誘導(dǎo)速度更快、強(qiáng)度更強(qiáng)。Xa7的過(guò)度表達(dá)或Xa7與avrXa7的共轉(zhuǎn)化引發(fā)了植物的超敏反應(yīng)。Xa7的組成性表達(dá)在Xoo缺失的情況下激活了防御反應(yīng)，但抑制了轉(zhuǎn)基因水稻的生長(zhǎng)。此外，對(duì)3000多個(gè)水稻品種的分析表明，Xa7基因位點(diǎn)主要存在于秈稻和aus亞群。在供試品種的EBEAvrXa7中發(fā)現(xiàn)了一個(gè)由11bp插入和堿基替換（G到T）組成的變異，導(dǎo)致了Xa7抗性的喪失。