Abstract
The Asian citrus psyllid, Diaphorina citri, is the vector of the bacterium “Candidatus Liberibacter asiaticus” (Las), associated with the devastating, worldwide citrus disease huanglongbing. In order to explore the molecular interactions of this bacterium with D. citri during the vector acquisition process, cDNA libraries were sequenced on an Illumina platform, obtained from the gut of adult psyllids confined in healthy (H) and in Las-infected young shoots (Las) for different periods of times (I = 1/2 days, II = 3/4 days, and III = 5/6 days). In each sampling time, three biological replicates were collected, containing 100 guts each, totaling 18 libraries depleted in ribosomal RNA. Reads were quality-filtered and mapped against the Chinese JXGC Las strain and the Floridian strain UF506 for the analysis of the activity of Las genome and SC1, SC2, and type 3 (P-JXGC-3) prophages of the studied Las strain. Gene activity was considered only if reads of at least two replicates for each acquisition access period mapped against the selected genomes, which resulted in coverages of 44.4, 79.9, and 94.5% of the JXGC predicted coding sequences in Las I, Las II, and Las III, respectively. These genes indicate an active metabolism and increased expression according to the feeding time in the following functional categories: energy production, amino acid metabolism, signal translation, cell wall, and replication and repair of genetic material. Pilins were among the most highly expressed genes regardless of the acquisition time, while only a few genes from cluster I of flagella were not expressed. Furthermore, the prophage region had a greater coverage of reads for SC1 and P-JXGC-3 prophages and low coverage in SC2 and no indication of activity for the lysis cycle. This research presents the first descriptive analysis of Las transcriptome in the initial steps of the D. citri gut colonization, where 95% of Las genes were active.
Highlights
The psyllid may acquire Liberibacter asiaticus” (Las) from symptomatic plants (Hung et al, 2004; Pelz-Stelinski et al, 2010; Canale et al, 2017; Lopes and Cifuentes-Arenas, 2021) as well as from asymptomatic citrus plants (Lee et al, 2015)
The obtention of D. citri gut samples with Las requires manipulation of individuals to dissect them while keeping the integrity of the organ and the quality and amount of mRNA necessary, in particular from the bacterium, to reveal genes whose transcription does occur in the psyllid gut
D. citri feeding on young citrus flushes infected by Las, under proper environmental conditions as those used in this study, generates high rates of infective psyllids, able to transmit Las at high rates as a consequence of the high bacterial titer in the psyllid (Lopes and Cifuentes-Arenas, 2021)
Summary
The psyllid may acquire Las from symptomatic plants (Hung et al, 2004; Pelz-Stelinski et al, 2010; Canale et al, 2017; Lopes and Cifuentes-Arenas, 2021) as well as from asymptomatic citrus plants (Lee et al, 2015). Gene expression studies showed a pattern of response in the gut and salivary glands of D. citri to Las infection (Kruse et al, 2017; Liu et al, 2020). There are exploratory studies that report transcriptional modifications in plants due to the presence of Las in Catharanthus roseus (Liu et al, 2019) and in leaves (Fu et al, 2016; Hu et al, 2017) and fruits of Citrus spp. The transcriptional mapping analysis of Las genes in the gut of D. citri that fed in Las-infected citrus was performed in this study, evidencing the expression of almost all genes of Las as a manner to generate knowledge in the initial phase of the Las infection in the psyllid
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