A Specific High Toxicity of Xinjunan (Dioctyldiethylenetriamine) to Xanthomonas by Affecting the Iron Metabolism

Xanthomonas spp. encompass a wide range of phytopathogens that brings great economic losses to various crops. Rational use of pesticides is one of the effective means to control the diseases. Xinjunan (Dioctyldiethylenetriamine) is structurally unrelated to traditional bactericides, and is used to control fungal, bacterial, and viral diseases with their unknown mode of actions. Here, we found that Xinjunan had a specific high toxicity toward Xanthomonas spp., especially to the Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of rice bacterial leaf blight. Transmission electron microscope (TEM) confirmed its bactericidal effect by morphological changes, including cytoplasmic vacuolation and cell wall degradation. DNA synthesis was significantly inhibited, and the inhibitory effect enhanced with the increase of the chemical concentration. However, the synthesis of protein and EPS was not affected. RNA-seq revealed differentially expressed genes (DEGs) particularly enriched in iron uptake, which was subsequently confirmed by siderophore detection, intracellular Fe content and iron-uptake related genes transcriptional level. The laser confocal scanning microscopy and growth curve monitoring of the cell viability in response to different Fe condition proved that the Xinjunan activity relied on the addition of iron. Taken together, we speculated that Xinjunan exerted bactericidal effect by affecting cellular iron metabolism as a novel mode of action. IMPORTANCE Sustainable chemical control for rice bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae need to be developed due to limited bactericides with high efficiency, low cost, and low toxicity in China. This present study verified a broad-spectrum fungicide named Xinjunan possessing a specific high toxicity to Xanthomonas pathogens, which were further confirmed by affecting the cellular iron metabolism of Xoo as a novel mode of action. These findings will contribute to the application of the compound in the field control of Xanthomonas spp.-caused diseases, and be directive for future development of novel specific drugs for the control of severe bacterial diseases based on this novel mode of action.