Applied and Basic Aspects of Copper Interaction with Xylella fastidiosa

Abstract

Xylella fastidiosa, a gram-negative, xylem-limited plant pathogenic bacterium that causes severe diseases and asymptomatic colonization in more than 600 different plants worldwide, including many economically important crops. Great economic impact and job losses are caused by this pathogen, therefore broad attention was drawing from science and society. Copper (Cu) as a widely used antimicrobial agent is hardly used to control X. fastidiosa in the field, but is often applied to its hosts for other pathogens’ management. High Cu accumulations in field soils were found in X. fastidiosa living environment and threatened its survival. In my dissertation, I attempted to understand the interactions between Cu and X. fastidiosa, especially in aspects of X. fastidiosa virulence, molecular basis of Cu resistance/homeostasis, and further features that may influence Cu resistance ability in X. fastidiosa. First, I conducted in planta experiments to determine the influence of Cu in X. fastidiosa infection using tobacco as a model. Uptake of Cu was noticed in plants treated with CuSO4- amended water. However, this did not help to control disease symptoms development, nor the growth of X. fastidiosa in planta. Then, molecular basis of Cu resistance/homeostasis was studied in relation to virulence. Mutants of Cu-related genes copA, copB and cutC were more sensitive to Cu than the wild-type (WT) strain. All the mutants increased disease severity under Cu-amended conditions, and the increments were higher than WT. Last, our analysis showed that no clear correlation was found between Cu resistance/homeostasis ability and X. fastidiosa phylogeny, host and/or location of isolation. In general, I found that Cu content in plant could influence virulence of X. fastidiosa. Cu resistance/homeostasis in X. fastidiosa is important for its in planta colonization and disease symptoms development, which is associated with copA, copB and cutC genes that function differently to fulfill Cu resistance/homeostasis. Meanwhile, Cu resistance/homeostasis in X. fastidiosa is not simply decided by host and/or location of isolation. My research help to unveil the mechanisms of Cu resistance/homeostasis in X. fastidiosa, and highlight the important role that Cu plays in X. fastidiosa full virulence as well as its interaction with host plants.