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LC2 and LC1 act as key regulators of bacteriophage SC1 in Liberibacter crescens

Alejandra Munoz Bodnar: University of Florida

<div>Most <em>Liberibacter asiaticus</em> (Las) genomes sequenced to date harbor bacteriophages with similarity to Florida Las strain UF506 SC1 and SC2. SC1 is maintained as a stable lysogen in psyllids but its lytic phase is activated in periwinkle and citrus. A C2-like (LC2) repressor is encoded on the SC1 bacteriophage that may be involved in the activation of the SC1 lytic cycle <em>in planta</em>. Different Las strains also chromosomally encode either a full length or a truncated version of a C1-like (LC1) repressor: one full and one truncated. The regulatory control mechanisms of the lytic cycle <em>in planta</em> and its demonstrated repression in psyllids is unknown. We hypothesize that both LC1 and LC2 could play important roles in repression of the lytic SC1 genes. Electrophoretic mobility shift assays (EMSAs) revealed that both LC1 versions as well as LC2 binds to the C2 promoter. To functionally test this hypothesis, the C2 promoter region was fused in both directions with a GFP reporter and these constructs were transformed into <em>Liberibacter crescens</em> (Lcr), along with expression plasmids expressing both LC1 and LC2. Interestingly, LC2 appeared to repress GFP expression, whereas both versions of LC1 seems to activate the C2 promoter. Both regulators are molecular targets for Las chemical control.</div>