Abstract
The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is the insect vector of the fastidious bacterium Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening disease, or Huanglongbing (HLB). The widespread invasiveness of the psyllid vector and HLB in citrus trees worldwide has underscored the need for non-traditional approaches to manage the disease. One tenable solution is through the deployment of RNA interference technology to silence protein-protein interactions essential for ACP-mediated CLas invasion and transmission. To identify psyllid interactor-bacterial effector combinations associated with psyllid-CLas interactions, cDNA libraries were constructed from CLas-infected and CLas-free ACP adults and nymphs, and analyzed for differential expression. Library assemblies comprised 24,039,255 reads and yielded 45,976 consensus contigs. They were annotated (UniProt), classified using Gene Ontology, and subjected to in silico expression analyses using the Transcriptome Computational Workbench (TCW) (http://www.sohomoptera.org/ACPPoP/). Functional-biological pathway interpretations were carried out using the Kyoto Encyclopedia of Genes and Genomes databases. Differentially expressed contigs in adults and/or nymphs represented genes and/or metabolic/pathogenesis pathways involved in adhesion, biofilm formation, development-related, immunity, nutrition, stress, and virulence. Notably, contigs involved in gene silencing and transposon-related responses were documented in a psyllid for the first time. This is the first comparative transcriptomic analysis of ACP adults and nymphs infected and uninfected with CLas. The results provide key initial insights into host-parasite interactions involving CLas effectors that contribute to invasion-virulence, and to host nutritional exploitation and immune-related responses that appear to be essential for successful ACP-mediated circulative, propagative CLas transmission.
Highlights
The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is the insect vector and host of Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening disease, known as Huanglongbing (HLB) [1,2,3]
Transcripts involved in gene silencing and TE activity were classified in biologically significant categories associated with CLas invasion and long-term host fitness that strongly implicate the activation of gene silencing pathways and TE accumulation [123]
The in silico comparative analyses of contigs in the CLas-infected and—uninfected nymph and adult stages showed many with predicted involvement in CLas invasion, adhesion, multiplication, biofilm formation, and nutritional parasitism
Summary
The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is the insect vector and host of Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening disease, known as Huanglongbing (HLB) [1,2,3]. In the U.S CLas was first detected in citrus trees in Florida during 2004–05, following the introduction of ACP there ten years before [3]. CLas has been confirmed infecting citrus trees in California, Florida, Georgia, Louisiana, South Carolina, and Texas (http://www.hungrypests.com/faqs/citrus-greening.php). Based on the relatively small genome size of CLas 1.23-Mb [14], the absence of plant-colonizing extracellular degradative enzymes, and the predicted, limited ability for aerobic respiration, the bacterium is predicted to utilize key host plant and probably psyllid metabolites, and has adopted an intracellular lifestyle with the host plant like its close relatives in the Rhizobiales [15], and has evolved a host-parasite relationship akin to certain other pathogens that engage in multi-partite interactions to enable dual host exploitation [16]
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