Identification and gene expression of multiple peptidoglycan recognition proteins (PGRPs) in the deep-sea mussel Bathymodiolus azoricus , involvement in symbiosis?

Abstract

The relationship between the deep-sea mussel Bathymodiolus azoricus and its thiotrophic (SOX) and methanotrophic (MOX) symbionts has been ecologically and functionally well studied.Endosymbiosis is common in deep-sea hydrothermal vent fauna, yet little is known about the molecular mechanisms underlying the regulation of interactions between host and symbionts. In this study we focused on a group of pattern recognition receptors (PRR), called PGRPs that are able to recognize the peptidoglycan of bacterial cell wall. We first characterised the different PGRPs isoforms in B. azoricus gills and identified five paralogs. Among them two displayed a signal peptide. Then, specific probes designed for each paralog were used to perform real-time PCR quantification in gills of individuals showing various bacterial content as a result of in situ experimental procedures. Overall we found a decrease of PGRPs expression when symbionts amount decreases, suggesting an implication of PGRPs in the regulation of symbionts in B. azoricus gills.We therefore hypothesize that secreted proteins could act as cooperation signals to induce colonisation of symbiotic tissue while non-secreted proteins may regulate the density of endosymbionts within the gill tissue.

Global host molecular perturbations upon in situ loss of bacterial endosymbionts in the deep-sea mussel Bathymodiolus azoricus assessed using proteomics and transcriptomics

“…The up-regulation of most of the PRRs at transcripts level only, supports this second hypothesis: mussels may have lined up storage of immune transcripts to respond adequately to a putative pathogen invasion. In contrast, the global down-regulation of another immune receptor (PGRP 3), seems to ascertain its role as a symbiont recruiter [36].…”

“…More recently, a metabolic interdependence between B. azoricus and its symbionts has been evidenced using a proteo-genomic approach comparing aposymbiotic and symbiotic tissues [34]. While none of these studies have been validated in situ, it is noteworthy that pioneering attempts to do so have shown the putative role of two families of immune proteins in symbionts’ recognition and regulation [35, 36]. Although significant in the understanding of symbiotic association in deep-sea environments, these studies were either performed ex situ or limited to specific processes or families of genes, restricting our understanding on the mechanisms established by the host to manage its symbionts.…”

Transcriptome analysis of air-breathing land slug, Incilaria fruhstorferi reveals functional insights into growth, immunity, and reproduction

“…Six short form PGRPs with conserved amidase activity have been revealed from Crassostrea gigas genome [72]. The lack of a signal peptide in the I. fruhstorferi PGRP_SC2 (If_PGRP_SC2) was in agreement to the short PGRPs screened from the EST database of deep- sea mussel, Bathymodiolus azoricus (Ba-PGRP 2 and Ba-PGRP 4) [73]. Further, the predicted secondary structure analysis for If_PGRP_SC2 show consistency with the three-dimensional model of BaPGRP 2 [73] and Drosophila PGRP-LB residues [74].…”

Identification and characterization of endosymbiosis-related immune genes in deep-sea mussels Gigantidas platifrons

“…As suggested, PRRs mediated immune recognition of symbionts could be the fi rst step in initializing symbiosis. To date, multiple PRRs including Toll-like receptors (TLRs), immunoglobulin superfamily members (IgSF), peptidoglycan recognition proteins (PGRPs), lectins, and complement molecule (C1q) have been reported in Bathymodioline mussels and suggested their irreplaceable role in symbiosis (Bettencourt et al, 2009;Martins et al, 2014;Détrée et al, 2017;Zheng et al, 2017). What's more, it was reported that G .…”