Abstract
CLIBASIA_01510, PrbP, is a predicted RNA polymerase binding protein in Liberibacter asiaticus. PrbP was found to regulate expression of a small subset of ribosomal genes through interactions with the β-subunit of the RNA polymerase and a short, specific sequence on the promoter region. Molecular screening assays were performed to identify small molecules that interact with PrbP in vitro. Chemical hits were analyzed for therapeutic efficacy against L. asiaticus via an infected leaf assay, where the transcriptional activity of L. asiaticus was found to decrease significantly after exposure to tolfenamic acid. Similarly, tolfenamic acid was found to inhibit L. asiaticus infection in highly symptomatic citrus seedlings. Our results indicate that PrbP is an important transcriptional regulator for survival of L. asiaticus in planta, and the chemicals identified by molecular screening assays could be used as a therapeutic treatment for huanglongbing disease.
Highlights
Liberibacter asiaticus is the prevalent causative agent of huanglongbing (HLB; citrus greening), the most devastating citrus disease worldwide
Genome analyses have revealed a drastic reduction of the genetic information encoded by the L. asiaticus genome, Tolfenamic Acid Inhibits L. asiaticus suggesting this microorganism is highly adapted to life within its host (Duan et al, 2009)
We explored the possibility of identifying specific ligands in vitro, that affect the activity of PrbP in vivo, as a means to disrupt gene expression, and decrease viability of L. asiaticus in the citrus host
Summary
Liberibacter asiaticus is the prevalent causative agent of huanglongbing (HLB; citrus greening), the most devastating citrus disease worldwide. Liberibacter asiaticus is a phloem-limited pathogen with uneven distribution throughout the plant It is transmitted by the Asian citrus psyllid Diaphorina citri and it behaves as intracellular plant pathogen and as an insect symbiont. PrbP shares low sequence identity with the transcription factor CdnL in Myxococcus xanthus and with CarD in the Mycobacteriaceae family (García-Moreno et al, 2010). Members of this protein family have been linked to pathogenesis, persistence, cell viability, and resistance to both antibiotics and environmental stress (Stallings et al, 2009; Stallings and Glickman, 2011; Weiss et al, 2012). PrbP represents an excellent therapeutic target for the design of antimicrobial strategies against L. asiaticus
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