Citrus phytochemicals as potential therapeutics against asiatic citrus psyllid and Candidatus Liberibacter asiaticus: targeting the tripartite interaction

Candidatus Liberibacter asiaticus (CLas), a phloem-limited alphaproteobacterium, is the predominant species associated with the devastating citrus disease Huanglongbing (HLB). It is transmitted by the insect Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (D. citri), which carries the infectious bacterium. The bacterium CLas exhibits host-specific gene expression to adapt to the distinct environments of insect and plant hosts. This study aimed to assess the underlying mechanism of HLB by conducting an in silico study, where 64 ACP proteins and 24 CLas proteins were docked with 67 citrus plant phytochemicals. Density functional theory (DFT) exploration was performed to evaluate the responsiveness of the compounds that showed the best binding energies. Additionally, protein-protein interaction was performed to explore the active partners in the disease display. Among these, nine ACP proteins, solute carrier organic transporter, muscarinic acetyl choline receptor DM1, glycerol kinase, oxygen-dependent choline dehydrogenase, equilibrative nucleoside transporter, thiamine transporter, vinculin, propionyl-CoA carboxylase alpha chain and zinc transporter demonstrated significantly higher binding with the three CLas proteins, outer membrane protein, membrane spanning protein and ABC transporter protein. To conclude further, three phytochemicals, Eriocitrin, Rhoifolin, and Narirutin, were identified with promising binding affinities against the maximum number of ACP and CLas proteins. DFT analysis revealed the high reactivity of these compounds, suggesting their potential role in the tripartite interaction in HLB.