Bacterial canker, caused by Xanthomonas citri spp.citri, is an important bacterial disease of citrus plants.The efficient preventive measure is to spray copper-based chemicals.This paper reported that the outer membrane protein XAC1347 is involved in chemical tolerance in X.citri spp.citri.The inhibition experiments on plates indicated that the maximum dilutions of 46% Cu (OH)2 and 33% SC · Cu (OH)2were 2000 and 2500 folds, respectively.In the 2000-fold dilution conditions,inhibition zones of mutant △XAC1347 were increased 10-fold and 5-fold.When interaction with citrus plants, the transcription levels of copA and copB were decreased 37% and 15% in mutant △XAC1347.Constitutive expression of XAC1347 gene in mutant partially restored the phenotypes.These results suggest that outer membrane protein XAC1347 of X.citrispp.citri plays a role in the tolerance to copper-based bactericides.