The Transcriptome of the Salivary Glands of Amblyomma aureolatum Reveals the Antimicrobial Peptide Microplusin as an Important Factor for the Tick Protection Against Rickettsia rickettsii Infection

• Published in: Frontiers in physiology Vol. 10; p. 529
• Main Authors: Martins, Larissa A, Malossi, Camila D, Galletti, Maria F B de M, Ribeiro, José M, Fujita, André, Esteves, Eliane, Costa, Francisco B, Labruna, Marcelo B, Daffre, Sirlei, Fogaça, Andréa C
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 03-05-2019
• Subjects: antimicrobial peptide; immune; microplusin; Physiology; salivary glands; spotted fever; tick-rickettsiae interaction; spotted fever; RNAi; immune; microplusin; transcriptome; salivary glands; antimicrobial peptide; tick-rickettsiae interaction
• ISSN: 1664-042X; 1664-042X
• DOI: 10.3389/fphys.2019.00529

The salivary glands (SG) of ixodid ticks play a pivotal role in blood feeding, producing both the cement and the saliva. The cement is an adhesive substance that helps the attachment of the tick to the host skin, while the saliva contains a rich mixture of antihemostatic, anti-inflammatory, and immunomodulatory substances that allow ticks to properly acquire the blood meal. The tick saliva is also a vehicle used by several pathogens to be transmitted to the vertebrate host, including various bacterial species from the genus
.
is a tick-borne obligate intracellular bacterium that causes the severe Rocky Mountain spotted fever. In Brazil, the dog yellow tick
is a vector of
. In the current study, the effects of an experimental infection with
on the global gene expression profile of
SG was determined by next-generation RNA sequencing. A total of 260 coding sequences (CDSs) were modulated by infection, among which 161 were upregulated and 99 were downregulated. Regarding CDSs in the immunity category, we highlight one sequence encoding one microplusin-like antimicrobial peptide (AMP) (Ambaur-69859). AMPs are important effectors of the arthropod immune system, which lack the adaptive response of the immune system of vertebrates. The expression of microplusin was confirmed to be significantly upregulated in the SG as well as in the midgut (MG) of infected
by a quantitative polymerase chain reaction preceded by reverse transcription. The knockdown of the microplusin expression by RNA interference caused a significant increase in the prevalence of infected ticks in relation to the control. In addition, a higher rickettsial load of one order of magnitude was recorded in both the MG and SG of ticks that received microplusin-specific dsRNA. No effect of microplusin knockdown was observed on the
transmission to rabbits. Moreover, no significant differences in tick engorgement and oviposition were recorded in ticks that received dsMicroplusin, demonstrating that microplusin knockdown has no effect on tick fitness. Further studies must be performed to determine the mechanism of action of this AMP against
.