Infection and distribution of Candidatus Liberibacter asiaticus in citrus plants and psyllid vectors at the cellular level

Abstract

Huanglongbing (HLB) is currently considered the most destructive disease of citrus worldwide. In the major citrus-growing areas in Asia and the US, the major causal agent of HLB is the bacterial pathogen Candidatus Liberibacter asiaticus (CLas). CLas is vectored by the Asian citrus psyllid, Diaphorina citri, in a persistent propagative manner. CLas cannot be cultured in vitro because of its unclear growth factors, leading to uncertainty in the infection mechanism of CLas at the cellular level in citrus and in D. citri. To characterize the detailed infection of CLas in the host and vector, the incidence of HLB was first investigated in citrus-growing fields in Fujian Province, China. It was found that the positive association of the level of CLas infection in the leaves correlated with the symptoms. Then antibodies against peptides of the outer membrane protein (OMP) of CLas were prepared and tested. The antibodies OMP-225, OMP-333 and OMP724 showed specificity to citrus plants in western blot analyses, whereas the antibodies OMP-47 and OMP-225 displayed specificity to the D. citri vector. The application of OMP-225 in the immunofluorescence assay indicated that CLas was located in and distributed throughout the phloem sieve cells of the leaf midribs and axile placenta of the fruit. CLas also infected the epithelial cells and visceral muscles of the alimentary canal of D. citri. The application of OMP-333 in immunoelectron microscopy indicated the round or oval CLas in the sieve cells of leaf midribs and axile placenta of fruit as well as in the epithelial cells and reticular tissue of D. citri alimentary canal. These results provide a reliable means for HLB detection, and enlighten a strategy via neutralizing OMP to control HLB. These findings also provide insight for the further investigation on CLas infection and pathogenesis, as well as CLas-vector interaction.

The greening-causing agent alters the behavioral and electrophysiological responses of the Asian citrus psyllid to a putative sex pheromone

“…Microorganisms infections may also negatively affect insect behavior through the central nervous system, as reported for the West Nile virus manipulating Culex mosquito host-seeking behavior 47 . As CLas infects multiple ACP tissues 48 , it is plausible that this bacterium may positively affect the peripheral nervous system by increasing transcript levels of acetic acid-detecting receptors while negatively affecting behavioral responses to acetic acid by infections to the central nervous system.…”

The greening-causing agent alters the behavioral and electrophysiological responses of the Asian citrus psyllid to a putative sex pheromone

“…Microorganisms infections may also negatively affect insect behavior through the central nervous system, as reported for the West Nile virus manipulating Culex mosquito host-seeking behavior. 47 As CLas infects multiple ACP tissues, 48 it is plausible that this bacterium may positively affect the peripheral nervous system by increasing transcript levels of acetic acid-Page15 detecting receptors while negatively affecting behavioral responses to acetic acid by infections to the central nervous system.…”

Interaction between the flagellum of Candidatus Liberibacter asiaticus and the vitellogenin-like protein of Diaphorina citri significantly influences CLas titer

“…L. africanus” ( C Laf) ( Bové, 2006 ; Andrade et al, 2020 ), C Las is the most aggressive and is transmitted by the Asian citrus psyllid (ACP, Diaphorina citri ) in a persistent-propagative manner ( Andrade et al, 2020 ; Zhou, 2020 ). After being ingested by D. citri from the phloem sap of diseased citrus, C Las initially infects the intestinal epithelium and then crosses the basal lamina into the midgut visceral muscles, from where it spreads into the hemolymph, followed by the salivary glands, and then back into citrus with the D. citri feeding process ( Wei and Li, 2016 ; Chen et al, 2022 ). The protein–protein interactions between the host and pathogen are extremely important for pathogen colonization, movement, and transmission.…”