Plants evolved a wide range of defense mechanisms against pathogens, e.g., morphological barriers, immunity systems, and chemical defense. Pathogens infect hosts to gain access to nutrients needed for reproduction. After initiation of infection, reproduction requires the full spectrum of essential nutrients. Host metabolites are also used as signals to trigger specific virulence mechanisms. We hypothesize that the host may try to limit access to nutrients and metabolites. Limitation of one single essential nutrient will protect the host. We further surmise that therefore, pathogens evolved active mechanisms to overcome such limitations. Similarly, the host may try to adapt metabolism to modulate metabolites used for signaling by the pathogen. We found that virulence of the important rice xylem pathogen Xanthomonas oryzae pv. oryzae (Xoo) depends critically on the ability to induce SWEET sucrose uniporters via Type III secretion system-mediated injection of Transcription Activator-Like effectors. Sucrose released by xylem parenchyma cells may serve either as a limiting nutrient for the pathogen, or as a critical signal, or both. This discovery enabled generation of rice elite varieties for Asia and Africa by genome editing with broad-spectrum resistance against diverse Xoo strains. The lines did not show obvious differences to controls in field tests. Thorough analysis validated effective outcrossing of transgenes used for editing. Elite lines are provided to government organizations in countries with suitable regulations for further dissemination. To prepare for the potential evolution of Xoo that overcome the resistance, we explore both the infection process, the use of sucrose by Xoo and the defense mechanisms of the host.
