Oral: The Impact of Vector-Borne Bacteria Pathogen on Associated Hosts
Genomic insights into citrus greening and its transmission.
D. GABRIEL (1), M. Jain (1), L. Fleites (1) (1) University of Florida, U.S.A.
Ca. Liberibacter asiaticus (Las) systemically infects Asian citrus psyllids without causing evident disease and is transmitted to citrus phloem, causing the severe disease Huanglongbing (HLB) after a surprisingly long incubation period. Las appears to be well adapted as one of several psyllid endosymbionts, but poorly adapted to citrus. Most Las strains described carry bacteriophage, and several phage genes have been identified as likely horizontally transferred lysogenic conversion factors, including a peroxidase, which suppresses a key citrus defense response. Several Las lytic phage late genes, including a functional holin, are activated in planta, but not in infected psyllids. The Las holin promoter was strongly active in driving a GUS reporter in L. crescens (Lcr), a culturable proxy for Las. Activity of the reporter in Lcr was suppressed by aqueous extracts from Las-free psyllids applied outside of the Lcr cells, indicating cell penetration and also partly explaining why Las has not been cultured to date. The suppressor activity was sensitive to heat and proteinase treatment and a repressor-like protein from the psyllid extracts was found to bind the holin promoter. This protein was identified by LC-MS/MS as a predicted secreted protein from Wolbachia, a common insect endosymbiont. The in vitro translated Wolbachia protein also penetrated Lcr cells and repressed the GUS reporter, indicating protein-mediated cross-species bacterial gene regulation.