Identifying key mechanisms of interaction in L. asiaticus-citrus pathosystem
Kaylie A. Padgett, Christopher L. Gardner, Danilo R. da Silva, Fernando A. Pagliai, Lei Pan, Marcelo Merli, Jose X. Chaparro, Graciela L. Lorca and Claudio F. Gonzalez
IFAS University of Florida, USA
Citrus greening disease, or huanglongbing, may entirely eradicate all varieties of citrus cultivars worldwide in the near future. Thus far there is no natural resistance identified in all citrus species and commercial cultivars analyzed. A diverse array of treatments used in the field has fallen short to identify effective methods to control this disease progression. Citrus greening is caused by Liberibacter species (L. asiaticus, L. americanus, L. africanus), a phloem restricted non-cultivable Gram negative bacteria, transmitted from tree to tree by an insect vector. The lack of reliable laboratory culturing conditions for this bacterium has significantly impaired the ability to rationally design effective therapeutic treatments to eliminate the pathogen from infected groves. There is a critical and urgent need to understand the bacteria’s basic biology to define new strategies for disease treatment. As such, the scientific research should be centered on efforts to define central mechanisms of host microbial interaction, thereby identifying vulnerabilities in the pathosystem. Our laboratory is using a functional genomics based approach to understand the fundamental biology of L. asiaticus. This experimental design was successfully used to elucidate biochemical aspects of key pathogenicity factors as well as for the selection of small molecules directed to inactivate vital metabolic pathways in L. asiaticus. We have demonstrated that the transcription factor LdtR is a central regulator of L. asiaticus physiology, modulating the expression of several genes potentially involved in pathogenesis. Together with the accessory protein PrbP, LdtR modulates the expression of key enzymes like LdtP, a transpeptidase/esterase involved in the peptidoglycan and LPS modification, and LotP, a chaperone interacting protein mediating L. asiaticus adaptation to the citrus host. Our findings suggest that the therapeutic treatments to eliminate L. asiaticus from the citrus hosts should be directed to the genetic mechanisms governing the early infection process, avoiding bacterial adaptation and persistence in the citrus host. Secondly, the LdtR regulon should be considered one of the most important targets to design potential strategies of control due to its wide transcriptional regulation.
Audience Take Away:
Dr Gonzalez is an Associate Professor at the University of Florida (UF). He obtained his PhD. at the National University of Tucuman, Argentina and completed his postdoctoral training at Stanford University, UCSD and UofT. He is a microbiologist expert in the field of genetic regulation, protein purification and enzyme characterization. His research team at UF is committed to identify and understand molecular mechanisms mediating host/microbiota interactions. The actual efforts of his research team is directed to define basic pathogenicity mechanisms of L. asiaticus to help the citrus industry survive the actual crisis as a consequence of citrus greening disease.