Vector–pathogen interfaces in citrus greening pathosystem

Worldwide, insect vector-borne plant pathogens are responsible for over seven hundred diseases. Hemipteran insectsincluding aphids, leafhoppers, whiteflies, and psyllids, are the main vectors of plant pathogens. Citrus greening, or huanglongbing (HLB), currently is the most devastating disease of citrus. HLB disease is putatively caused by the phloem-restricted α-proteobacterium ‘Candidatus Liberibacter asiaticus’.This bacterium is transmitted primarily by the Asian citrus psyllid Diaphorina citri (Hemiptera: Liviidae). The relationship of ‘Ca. L. asiaticus’ with its insect vector, D. citri, has been well investigated at the molecular, biochemical, and biological levels. The findings concerning this relationship and molecular features of the acquisition of ‘Ca. L. asiaticus’ from the plant host and its growth and circulation within D. citri, as well as its transmission to plants, will be presented. ‘Ca. L. asiaticus’ affects the energy metabolism (respiration, tricarboxylic acid cycle, and adenosine triphosphate production), metabolic pathways, immune system, endosymbionts, and detoxification enzymes of D. citri. This led to shorter lifespan, altered feeding behavior, and higher fecundity. Although ‘Ca. L. asiaticus’ has significant negative effects on its insect vector, it increases its vector fitness, indicating that it develops a mutualistic relationship with its vector to secure more efficient spread of the disease.Understanding the specific interactions between ‘Ca. L. asiaticus’ and its psyllid vector will help design innovative management strategies.