Peptide Conjugated Morpholinos for Management of The Huanglongbing Pathosystem

BACKGROUND: 'Candidatus Liberibacter asiaticus' (CLas) is the causal agent of the devastating citrus disease Huanglongbing (HLB) and is transmitted by the insect vector Diaphorina citri (Hemiptera: Liviidae). A potential approach for treating CLas infection is the use of synthetic nucleic acid-like oligomers to silence bacterial gene expression. Peptide conjugated morpholinos (PPMOs) targeting essential genes in CLas and the psyllid vector's endosymbiotic bacteria, Wolbachia (wDi), were evaluated using in vitro and in vivo assays. RESULTS: Expression of the wDi gyrA gene was significantly reduced following incubation of Wolbachia cells with PPMOs. In addition, the viability of isolated wDi cells was greatly reduced when treated with PPMOs as compared to untreated cells. Feeding D. citri adults with a complementary PPMO (CLgyrA-14) significantly reduced the expression of CLas gyrA gene by 70%. CLas relative density was significantly lower in the psyllids fed with CLgyrA-14, when compared to untreated insects. Psyllids that were treated with CLgyrA-14 were less successful in transmitting the pathogen into uninfected plants, compared to untreated insects. CONCLUSION: The expression of essential genes in the D. citri symbiont, Wolbachia, and the HLB pathogen were suppressed in response to PPMO treatments. This study demonstrates the potential of PPMOs as a novel strategy for management of bacterial pathogens of fruit trees, such as HLB.