Copper-induced stress mechanisms in Erwinia amylovora: a comparative phenotypic and transcriptomic study using copper-sensitive and -tolerant strains
Erwinia amylovora causes fire blight. Copper is widely used for fire blight management but there is limited information on the pathogen's copper homeostasis mechanisms. Upon identifyingE. amylovora strains with unusually high (EaR2, Ea17) and intermediate (Ea19) copper sensitivity, we characterized them phenotypically to find potential correlations with other traits.The highly copper-sensitive strains EaR2 and Ea17 grew slower, showed increased sensitivity to paraquat and cadmium, and developed a characteristic copper-dependent overproduction of amylovoran and levan, with patterns not observed in strain, Ea273, with regular copper tolerance. Copper sensitivity was also associated with higher copper-shock death rates after copper pre-exposure during growth. RNA-Seq analysis revealed similar responses to copper-shock in EaR2 and Ea273 but very different transcriptomic responses during copper adaptation(prolonged growth with copper). EaR2 responded to copper adaptation with earlier activation ofstress responses, exopolysaccharide biosynthesis pathways, and protein quality control systems, while reducing the expression of genes linked to iron uptake. Ea273 mostly displayed an activation of copper homeostasis-related genes, with a characteristic downregulation of histidine catabolism. Overall design: RNA-seq profiling of copper shock and copper adaptation responses in Erwinia amylovora strains with regular and hypersensitive copper tolerance