Abstract
Copper-based compounds are widely used in agriculture as a chemical strategy to limit the spread of multiple plant diseases; however, the continuous use of this heavy metal has caused environmental damage as well as the development of copper-resistant strains. Thus, it is important to understand how the bacterial phytopathogens evolve to manage with this metal in the field. The MqsRA Toxin–Antitoxin system has been recently described for its function in biofilm formation and copper tolerance in Xylella fastidiosa, a plant-pathogen bacterium responsible for economic damage in several crops worldwide. Here we identified differentially regulated genes by X. fastidiosa MqsRA by assessing changes in global gene expression with and without copper. Results show that mqsR overexpression led to changes in the pattern of cell aggregation, culminating in a global phenotypic heterogeneity, indicative of persister cell formation. This phenotype was also observed in wild-type cells but only in the presence of copper. This suggests that MqsR regulates genes that alter cell behavior in order to prime them to respond to copper stress, which is supported by RNA-Seq analysis. To increase cellular tolerance, proteolysis and efflux pumps and regulator related to multidrug resistance are induced in the presence of copper, in an MqsR-independent response. In this study we show a network of genes modulated by MqsR that is associated with induction of persistence in X. fastidiosa. Persistence in plant-pathogenic bacteria is an important genetic tolerance mechanism still neglected for management of phytopathogens in agriculture, for which this work expands the current knowledge and opens new perspectives for studies aiming for a more efficient control in the field.
Highlights
Xylella fastidiosa is a phytopathogen with a broad host range that affects plants worldwide (Almeida et al, 2019)
Our results show that MqsR is a key gene regulator in the pathway tolerance of X. fastidiosa to copper stress, mediating several genes that prompt the cells to enter in a state that suggests the formation of persisters
To access the phenotypic and genetic regulation mediated by MqsR, we used the same condition, where copper was added after 15 days of bacterial growth
Summary
Xylella fastidiosa is a phytopathogen with a broad host range that affects plants worldwide (Almeida et al, 2019). Plant diseases caused by this bacterium include citrus variegated chlorosis (CVC), Pierce’s disease (PD) in grapevines, and the olive quick decline syndrome (OQDS), which constitute important threats for these crops (Almeida et al, 2019; Saponari et al, 2019; Coletta-Filho et al, 2020). Copper has an important contribution in crop protection; there are many issues related to the use of this heavy metal such as phytotoxicity, soil accumulation, negative effects on soil biota, and development of copper-resistant strains (Lamichhane et al, 2018). Regarding plant-pathogen interaction, it is important to understand how the bacterial phytopathogens evolve to deal with this metal in the field
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