Identification and functional analysis of the peptidoglycan recognition protein LD gene in the mosquito, Armigeres subalbatus

Peptidoglycan recognition proteins are important recognition proteins in many organisms ranging from echinoderms to humans. In an attempt to characterize all the PGRPs in the mosquito Armigeres subalbatus, two PGRP-LD isoforms, AsPGRP-LDa and AsPGRP-LDb, which are orthologs of the PGRP-LDs in several other insect species, were identified from this mosquito using homologous cloning. To date the functions of this PGRP gene have not yet been described in detail in other organisms with a known PGRP-LD gene. In the current study, we analyzed the sequences of these AsPGRP-LDs, their evolutionary relationships with their orthologs, their transcriptional expression in various developmental stages and different tissue samples, and their transcriptional responses to different bacterial stimuli. We then knocked down the expression of both AsPGRP-LDs by injection of double-stranded RNAs, and assessed the impact of AsPGRP-LD RNAi on mosquito survival after bacterial challenges and on the transcriptional expression of a number of antimicrobial peptides.