Poster Session: Molecular and Cellular Plant-Microbe Interactions - Molecular Plant-Microbe Interactions
699-P
Quorum sensing controls Candidatus Liberibacter asiaticus interactions with host plant and insect vector .
N. KILLINY (1)
(1) University of Florida, Citrus Research and Education Center, Lake Alfred, FL, U.S.A.
The typical LuxR bacterial "quorum sensing" or cell-to-cell communication system consists of two components, LuxR protein and Acyl-Homoserine Lactone (AHL). Genome of Candidatus Liberibacter asiaticus (CLas) contains luxR gene that encodes LuxR protein and the absence of luxI to produce AHL. We have confirmed the functionality of the CLas-LuxR by constructing a luxR gene promoter fused with a GFP reporter to generate a functional CLas luxR::GFP monitor E. coli. Several AHLs as well as extractions from insect, Diaphorina citri- Asian citrus psyllid (ACP) vector of CLas, or from the citrus plant, have been shown to activate CLas-luxR. The plant derived extracts may functionally be related to AHL but likely to be structurally unrelated. As a response to infection by CLas, citrus plants may induce the production of AHL mimic(s), which would bind to LuxR and trigger cell aggregation, and consequently limit bacterial growth and movement in planta. Additionally, the psyllid extract AHL produced by the endosymbiontic bacteria may bind to CLas-LuxR. As a result of this binding, Clas form biofilm on the surface of ACP gut. We expressed CLas LuxR in citrus using the CTV-based vector system. These citrus plants showed evenly distributed severe symptoms when infected with HLB (by graft inoculation). However, infection of healthy LuxR-citrus plants by CLas positive ACP (‘hot’ psyllids) showed diminished CLas titer. Thus, study of how CLas cells communicate in citrus and psyllids would help understanding the pathogenicity and transmission of this bacterium and potentially will lead to identify compounds that interfere with its growth and biofilm formation.