Table 1.

Evidence of invertebrate PRR and GPCR function in host-microbiota communication.

	Genomic Featuresa	Role in the metaorganism	References
Porifera	TIR-Ig domain receptors Expansion of NLRs, SRs No PGRPs	SRCR up-regulated in symbiotic vs. aposymbiotic sponges	(19–24)
Cnidaria	TLRs in Nematostella but lack of bona fide TLR in Hydra and corals Hydra spp. lack bona fide NLRs; NLR expansion in Nematostella SRs expansion in corals	Bacterial colonization in Hydra mediated by MyD88 Enhanced expression of SRs in symbiotic vs. aposymbiotic anemones. Impaired colonization if blocking SRs	(25–33)
Annelida	TLR expansion in Capitella teleta Unclear function of PRRs		(34)
Mollusca	TLR expansion in certain species	PGRPs in symbiosis establishment in Euprymna scolopes	(35–39)
Nematoda	No NLRs or PGRPs Expansion of CTLRs and GPCRs	C. elegans TLR encoding gene tol-1 for the protective effect of the Enterococcus faecium-derived secreted peptidoglycan hydrolase that enhances host tolerance to Salmonella infection CTLRs in microbiota recognition and aggregation in the cuticle of the marine nematode Laxus oneistus	(40–46)
Arthropoda	Highly diverse phylum and, accordingly, genomic features depend on the group	TLRs no key role in symbiosis Mosquito CTLRs for facilitating microbiota persistence in the gut. Shrimp CTLR-mediated prevention of gut microbiota overgrowth PGRP and Imd pathway key in gut-microbiota interactions GPCRs: potential role in microbiota vs. pathogen distinction in Drosophila	(47–63)
Echinodermata	Expansion of NLRs and SRs		(64–67)

Silhouette images downloaded from PhyloPic or drawn by the Authors in Inkscape (no copyright).

^aAccording to specified references and/or Buckley and Rast (64). CTLR, C-type lectin receptors; GPCR, G-protein coupled receptor; Ig, immunoglobulin; NLR, NOD-like receptor; PGRP, peptidoglycan recognition protein; PRR, pattern recognition receptor; SR, scavenger receptor; SRCR, scavenger receptor cysteine-rich; TIR, Toll-Interleukin receptor; TLR, Toll-like receptor.