Candidatus Liberibacter asiaticus carries a chromosomal CI phage repressor homolog that binds a bacteriophage promoter and may be required for prophage maintenance
L. FLEITES (1), M. Jain (1), S. Zhang (1), D. Gabriel (1) (1) University of Florida, U.S.A.

Huanglongbing, comm caused by Candidatus Liberibacter asiaticus (Las), is arguably the most devastating disease of citrus, causing severe production losses and tree death. 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 chromosomally encoded C1 phage repressor which may contribute to the maintenance of lysogeny. This C1 repressor contains a variable number of internal, 7 bp direct repeats which can recombine, causing frameshifts leading to the translation of truncated proteins.  Las strain UF506 has been maintained in isolation in a containment facility and transmitted from citrus to periwinkle via dodder.  All five C1 repressor sequences independently isolated from UF506 infected citrus encoded a full-length protein. In contrast, all seven independently isolated sequences derived from UF506 infected periwinkle encoded a truncated, frame-shifted version.  Phage particles are readily observed in UF506 infected periwinkle, but not in citrus.  Mobility shift assays demonstrated specific binding of both the full-length and truncated Las C1 repressor protein to its own promoter as well as an early gene promoter on the Las lytic phage.  We are evaluating promoter reporters to quantify repression in the presence of the full-length and truncated protein. The truncation may affect binding cooperativity, allowing lytic cycle completion in periwinkle.

Abstract Number: P7-167
Session Type: Poster