Numerous peptidoglycan recognition protein genes expressed in the bacteriome of the green rice leafhopper Nephotettix cincticeps (Hemiptera, Cicadellidae)

Peptidoglycan recognition proteins (PGRPs) contribute to the immune response of vertebrates and higher invertebrates. Animals have a varying number of PGRP genes: 4 in human and mouse, 13 in Drosophila, and 0 in an aphid. Transcriptome analyses revealed that numerous PGRP genes (> 300 in an RNA-Seq analysis) were expressed in the green rice leafhopper Nephotettix cincticeps (Uhler) (Hemiptera, Cicadellidae). PGRP genes were mostly expressed in the bacteriomes, in which two bacterial endosymbionts, Sulcia and Nasuia, are harbored. E. coli inoculation upregulated antimicrobial peptide gene expression in the leafhopper, whereas PGRP gene expression was not affected by the bacterial challenge. High and constant expression of PGRP genes in the bacteriomes and the lack of an immune response against invading bacteria suggest that these PGRPs play a hitherto unknown role in the bacteriomes, implicating a relationship with symbiotic association in N. cincticeps.