Dynamic integration and excision of filamentous phage XacF1 in pv. , the causative agent of citrus canker disease.

Inovirus XacF1 (7325 nucleotides) is integrated into the genome of pv. () strains at the host site (B) by the host XerC/D recombination system. The XacF1 P sequence is located within the coding region of ORF12, a possible phage regulator. After integration, this open reading frame (ORF) is split into two pieces on the host genome. We examined dynamic integration/excision of XacF1 in strain MAFF 301080 and found that the integration started at 4 h postinfection (p.i.) and peaked at 12 h p.i. Thereafter, the ratio of integrated to free forms remained constant, suggesting equilibrium of integration and excision of XacF1 in the host genome. However, the integrated state became very unstable following a 5'-deletion of ORF12 in XacF1, suggesting that ORF12 plays a key role in the integration cycle of XacF1 in strains.