AraC/XylS Family Stress Response Regulators Rob, SoxS, PliA, and OpiA in the Fire Blight Pathogen Erwinia amylovora

Abstract

bTranscriptional regulators of the AraC/XylS family have been associated with multidrug resistance, organic solvent tolerance, oxidative stress, and virulence in clinically relevant enterobacteria. In the present study, we identified four homologous AraC/ XylS regulators, Rob, SoxS, PliA, and OpiA, from the fire blight pathogen Erwinia amylovora Ea1189. Previous studies have shown that the regulators MarA, Rob, and SoxS from Escherichia coli mediate multiple-antibiotic resistance, primarily by upregulating the AcrAB-TolC efflux system. However, none of the four AraC/XylS regulators from E. amylovora was able to induce a multidrug resistance phenotype in the plant pathogen. Overexpression of rob led to a 2-fold increased expression of the acrA gene. However, the rob-overexpressing strain showed increased resistance to only a limited number of antibiotics. Furthermore, Rob was able to induce tolerance to organic solvents in E. amylovora by mechanisms other than efflux. We demonstrated that SoxS from E. amylovora is involved in superoxide resistance. A soxS-deficient mutant of Ea1189 was not able to grow on agar plates supplemented with the superoxide-generating agent paraquat. Furthermore, expression of soxS was induced by redox cycling agents. We identified two novel members of the AraC/XylS family in E. amylovora. PliA was highly upregulated during the early infection phase in apple rootstock and immature pear fruits. Multiple compounds were able to induce the expression of pliA, including apple leaf extracts, phenolic compounds, redox cycling agents, heavy metals, and decanoate. OpiA was shown to play a role in the regulation of osmotic and alkaline pH stress responses.

Transcriptional response of Erwinia amylovora to copper shock: in vivo role of the copA gene

“…However, both our current study with Ea and the previous study with E. coli include the hitherto identified copA gene, encoding a Cu + ‐translocating P‐type ATPase pump that exports copper from the cytoplasm to the periplasm, which is directly involved in the maintenance of copper homeostasis in E. coli (Rensing et al ., ; Yamamoto and Ishihama, ). In addition to copA , the transcription factor for the superoxide response regulon SoxS was also activated by copper (Pletzer et al ., ; Yamamoto and Ishihama, ). We observed some differences in gene expression between the microarray results and quantitative real‐time PCR for a few of the genes examined, most notably copA .…”

Comparative transcriptome analysis of a lowly virulent strain of Erwinia amylovora in shoots of two apple cultivars – susceptible and resistant to fire blight

“…These systems include two component signal transduction systems (TCSTs), regulating amylovoran biosynthesis and swarming motility [ 6 , 7 ], c-di-GMP, which positively regulates the secretion of the main exopolysaccharide in E. amylovora , amylovoran, leading to increased biofilm formation and quorum sensing [ 8 , 9 ], the bacterial alarmone ppGpp, crucial for T3SS regulation [ 10 ], and small RNAs (sRNAs) [ 11 ]. For successful infection other important factors are: i/ motility [ 12 ], ii/ biofilm formation [ 5 ], iii/ adhesion [ 13 ], iv/ stress responses including efficient expulsion of a wide range of compounds toxic to bacteria [ 14 , 15 ], v/ resistance towards host plant toxins, such as phytoalexins [ 16 ], vi/ adaptation to the environmental niche via catabolism of available carbohydrates, such as sucrose [ 17 ] and sorbitol [ 18 ], vii/ production of siderophores for iron acquisition [ 19 ], viii/ the production of metalloproteases, which are important for tissue colonization [ 20 ].…”

Backbone Interactions Between Transcriptional Activator ExsA and Anti-Activator ExsD Facilitate Regulation of the Type III Secretion System in Pseudomonas aeruginosa

“…II type transcriptional activator belonging to the prominent AraC/XylS family of proteins 20 . AraC proteins are involved in regulating a variety of processes, including cellular metabolism and virulence [22][23][24][25][26][27][28][29][30][31] . The characteristic AraC domain consists of two helix-turn-helix motifs that bind to cognate promoter elements 26 .…”