Map-Based Cloning of Rice Bacterial Blight Resistance Gene Xa23

Natural selection drives pathogens to acquire new effectors to avoid effector-triggered immunity (ETI); reciprocally, natural selection also drives plants to evolve new resistance (R) genes to recognize these effectors and trigger ETI. However, how new R genes have evolved to interact with diverse effectors remains largely unknown. Here, we adopted a map-based cloning approach and transcription activator-like effector(TALE)-based technology to isolate and characterize Xa23, a new executor R gene derived from wild rice (Oryza rufipogon) that confers broad-spectrum resistance against bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo). XA23 can trigger strong hypersensitive response in rice, tobacco and tomato. Resistant (Xa23) and susceptible (xa23) alleles of rice varieties have identical open reading frames, but different upstream regulatory regions, with and without the effector binding-element(EBE), respectively. In resistant varieties, the AvrXa23 TALE activates Xa23 expression during Xoo infection, thereby producing disease resistance. Xa23 triggers the hypersensitive response in monocots and dicots, indicating that it may have wide utility in engineering disease resistance in crop plants.