Gene silencing of ribosomal protein P0 is lethal to the tick Haemaphysalis longicornis.

Ribosomal protein P0 has been demonstrated to be a multifunctional protein in the large subunit of eukaryotic ribosome. In this study, a gene encoding ribosomal protein P0 termed HlP0 was isolated from a full-length salivary gland cDNA library previously constructed from the tick Haemaphysalis longicornis. The full-length cDNA of the HlP0 gene is 1141 bp, with an open reading frame (ORF) of 963 bp. The ORF of the HlP0 gene encodes a putative protein of 320 amino acid residues, with a predicted molecular mass of 35 kDa. Reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated that the HlP0 gene transcript was expressed in all developmental stages and all tissues dissected from 4-day-fed adult ticks. Antibodies raised against recombinant HlP0 recognized a native protein with an expected molecular size of 35 kDa in all tested tissues. RNA interference of HlP0 gene was carried out by injecting ticks with PBS, green fluorescent protein (GFP) dsRNA, and HlP0 dsRNA. The results showed that ticks treated with HlP0 dsRNA obtained a strikingly lower body weight (2.63+/-1.21 mg vs. 226.75+/-74.80 mg in the PBS-injected group and 231.15+/-51.32 mg in the GFP dsRNA-injected group, Student's t-test, P<0.01), a lower engorgement rate (4% vs. 100% and 94.11%, respectively), and higher mortality (96% vs. 2.5% and 10.4%, respectively) after blood-sucking than the control groups. This suggests that ribosomal protein P0 is required for the blood ingestion and subsequent viability of H. longicornis. This is the first report of ribosomal protein P0 from ticks.