Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2010
Publication Date: 4/1/2011
Citation: Zhang, S., Flores-Cruz, Z., Kang, B., Fleites, L., Wulff, N., Davis, M.J., Zhou, L., Duan, Y., Gabriel, D. 2011. Ca. Liberibacter asiaticus carries two prophage lysogens - one replicating as an excision plasmid and another that becomes lytic in plant infections. Molecular Plant-Microbe Interactions. 11(4):458-468. Interpretive Summary:
Technical Abstract: Huanglongbing (HLB), also known as citrus greening, is a lethal disease of citrus caused by several species of Candidatus Liberibacter, a psyllid transmitted, phloem limited, alpha proteobacteria. Ca. Liberibacter asiaticus (Las) is widespread in Florida citrus. The recently published Las strain psy62 genome, derived from a psyllid, revealed a prophage-like region of DNA in the genome, but phage have never been associated with Las. In the present study, shotgun sequencing and a fosmid DNA library of curated Las strain UF506, originally derived from citrus symptomatic for HLB, revealed two largely homologous, circular phage genomes, SC1 and SC2 belonging to the Podoviridae. SC2 encoded putative adhesin and peroxidase genes that had not previously been identified in Las and which may be involved in lysogenic conversion. SC2 also appeared to lack lytic cycle genes and replicated as a plasmid in both psyllids and in planta. By contrast, SC1 carried suspected lytic cycle genes and was found in nonintegrated, lytic cycle forms only in planta. Phage particles associated with Las were found in the phloem of infected periwinkles by transmission EM. Both SC1 and SC2 were organized in tandem array as prophage in the UF506 chromosome. In psyllids, both SC1 and SC2 were found only as prophage.