Unravelling the Pathogenesis and Molecular Interactions of Liberibacter Phytopathogens with Their Psyllid Vectors

Insect-borne bacterial pathogens pose a global economic threat to many agricultural crops. Candidatus liberibacter species, vectored by psyllids (Hemiptera: psylloidea), are an example of devastating pathogens related to important known diseases such as Huanglongbing or the citrus greening disease, Zebra chip disease, and carrot yellowing, along with vegetative disorders in umbellifers. Studies on liberibacter–plant interactions have gained more focus in disease control over the last few decades. However, successful and sustainable disease management depends on the early disruption of insect–pathogen interactions, thereby blocking transmission. Recent knowledge on the liberibacter genomes and various omics approaches have helped us understand this host–pathogen relationship, despite the complexity associated with the inability to culture these bacteria. Here, we discuss the cellular and molecular processes involved in the response of insect-host immunity, and the liberibacter-associated pathogenesis mechanisms that involve virulence traits and effectors released to manipulate the insect–host defense mechanism for successful transmission. Understanding such mechanisms is an important milestone for developing sustainable means for preventing liberibacter transmission by psyllids.