APS Homepage

Poster: Molecular & Cellular Plant-Microbe Interactions: MPMI


Ca. Liberibacter asiaticus carries a highly conserved, chromosomal CI repressor that binds an early gene promoter in its prophage.
L. FLEITES (1), M. Jain (1), S. Zhang (1), D. Gabriel (1) (1) University of Florida, Gainesville, FL, U.S.A.

Candidatus Liberibacter asiaticus (Las) is one of three species of bacteria associated with Huanglongbing, arguably the most devastating disease of citrus. The majority of Las strains harbor bacteriophage that are maintained as stable lysogens in psyllids, but begin to enter a lytic cycle in planta. Las carries a CI phage repressor (LCI) with internal direct repeats that readily recombine and can create truncated translation products. LCI has been used as an epidemiological marker to follow the movement of Las populations; however, LCI has not been functionally characterized. Las strain UF506 has been maintained in isolation in a containment facility and transmitted from citrus to citrus and to periwinkle via dodder. All five LCI sequences isolated from curated Las strain UF506 in infected citrus encoded a full-length protein. By contrast, all seven UF506 LCI sequences derived from artificially infected periwinkle encoded a truncated version. Mobility shift assays demonstrated that LCI binds its own promoter and an early gene promoter on SC1, indicating potential involvement in lytic cycle activation. Promoter reporters are being evaluated to quantify repression in the presence of the full-length and truncated proteins, and additional potential binding sites are being investigated. If the LCI does function as a phage repressor, it would become a promising target for HLB control, since interfering with this function could trigger the lytic cycle in Las.