Xa1-mediated resistance to rice bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo), is triggered by transcription activator-like effectors (TALEs) and suppressed by interfering TALEs (iTALEs). TALEs interact with the rice transcription factor OsTFIIAγ1 or OsTFIIAγ5 (Xa5) to transcriptionally activate expression of target resistance and/or susceptibility genes. However, it is not clear whether OsTFIIAγ is involved in TALE-triggered and iTALE-suppressed Xa1 resistance. In this study, genome-edited mutations in OsTFIIAγ5 or OsTFIIAγ1 of Xa1-containing rice IRBB1 and Xa1-transgenic plants of xa5-containing rice IRBB5 did not impair the activation or suppression of Xa1 resistance. Correspondingly, the expression pattern of Xa1 in mutated OsTFIIAγ5 and OsTFIIAγ1 rice lines and IRBB1 rice was similar. In contrast, the expression of OsSWEET11 was repressed in mutated OsTFIIAγ5 and OsTFIIAγ1 rice lines. Biomolecular fluorescence complementation (BiFC) and co-immunoprecipitation (Co-IP) showed that both the TALE PthXo1 and iTALE Tal3a interacted with OsTFIIAγ1 and OsTFIIAγ5 in plant nuclei. These results indicate that TALE-triggered and iTALE-suppressed Xa1 resistance to BB is independent of OsTFIIAγ1 or OsTFIIAγ5 in rice and suggest that an unknown factor is potentially involved in the interaction of Xa1, TALEs and iTALEs in rice.
黃單胞菌TALE蛋白需要與植物基礎轉錄因子TFIIAγ形成復合體啟動寄主靶標基因的轉錄表達。本研究通過體外生化試驗與轉基因水稻材料的抗病性測定，不僅發(fā)現了TALE和iTALE蛋白都能夠與OsTFIIAγ1和OsTFIIAγ5互作，而且還發(fā)現TALE激活和iTALE抑制Xa1抗性，不依賴于水稻基礎轉錄因子OsTFIIAγ1和OsTFIIAγ5。同時，還明確了Xa1定位于植物細胞核，提示Xa1抗性的激活與抑制發(fā)生在植物細胞核中。
水稻Xa1抗性可被稻黃單胞菌95%以上的菌株所克服，原因在于這些菌株均含有iTALE，這也是Xa1基因在水稻白葉枯病抗病育種中不被廣泛應用的原因。經非寄主煙草上HR測定和平行試驗，推測Xa1抗性的激發(fā)和抑制可能是通過與水稻中未知因子在蛋白質水平上相互作用的結果。因此，解析Xa1抗性被抑制的機理，將為培育廣譜持久抗白葉枯病水稻具有重要的實踐意義。