The transcriptional activator LdtR from 'Candidatus Liberibacter asiaticus' mediates osmotic stress tolerance.
The causal agent of Huanglongbing disease, 'Candidatus Liberibacter asiaticus', is a non-culturable, gram negative, phloem-limited α-proteobacterium. Current methods to control the spread of this disease are still limited to the removal and destruction of infected trees. In this study, we identified and characterized a regulon from 'Ca. L. asiaticus' involved in cell wall remodeling, that contains a member of the MarR family of transcriptional regulators (ldtR), and a predicted L,D-transpeptidase (ldtP). In Sinorhizobium meliloti, mutation of ldtR resulted in morphological changes (shortened rod-type phenotype) and reduced tolerance to osmotic stress. A biochemical approach was taken to identify small molecules that modulate LdtR activity. The LdtR ligands identified by thermal shift assays were validated using DNA binding methods. The biological impact of LdtR inactivation by the small molecules was then examined in Sinorhizobium meliloti and Liberibacter crescens, where a shortened-rod phenotype was induced by growth in presence of the ligands. A new method was also developed to examine the effects of small molecules on the viability of 'Ca. Liberibacter asiaticus', using shoots from HLB-infected orange trees. Decreased expression of ldtRLas and ldtPLas was observed in samples taken from HLB-infected shoots after 6 h of incubation with the LdtR ligands. These results provide strong proof of concept for the use of small molecules that target LdtR, as a potential treatment option for Huanglongbing disease.
Microbiology and Cell Science Department, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America.
Fernando A
FA
Pagliai
Microbiology and Cell Science Department, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America.
Christopher L
CL
Gardner
Microbiology and Cell Science Department, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America.
Lora
L
Bojilova
Microbiology and Cell Science Department, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America.
Amanda
A
Sarnegrim
Microbiology and Cell Science Department, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America.
Cheila
C
Tamayo
Microbiology and Cell Science Department, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America.
Anastasia H
AH
Potts
Microbiology and Cell Science Department, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America; Soil and Water Science Department, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America.
Max
M
Teplitski
Department of Plant Pathology, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America.
Svetlana Y
SY
Folimonova
Microbiology and Cell Science Department, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America.
Claudio F
CF
Gonzalez
Microbiology and Cell Science Department, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, Florida, United States of America.
Graciela L
GL
Lorca
D001419:Bacteria / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002957:Citrus / Q000382:microbiology*; D009997:Osmotic Pressure; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D015534:Trans-Activators