RNAseq-based gene expression analysis of Melolontha hippocastani hindgut pockets and the surrounding hindgut wall tissue

In this study, the metatranscriptome of newly-discovered structures attached at the distal end of the hindgut of the larvae of a coleopteran (Melolontha hippocastani), is compared with that of the surrounding hindgut wall. Larvae were collected in their natural habitat, RNA was extracted using a commercial kit and sequenced in a Illumina HiSeq2500 platform. 250 bp paired-end reads were used to de novo assemble the transcriptomes. Contig annotation was carried out with BLASTx and Blast2GO PRO and differential expression analysis was performed in edgeR. Contigs aligned mainly to Achromobacter sp. in the pockets and to the Firmicutes phylum in hindgut wall. Host RNAs were expressed in the pockets in higher amounts than in hindgut wall. Gene expression suggest that pocket bacteria undergo aerobic metabolism and are exposed to higher levels of oxidative stress than the population of the hindgut wall. Hypothetical functions for the pocket might be immune-stimulation and regulation of host development, while the hindgut wall appears to be devoted to degradation of dietary polysaccharides and host nitrogenous wastes. Further research is necessary to experimentally prove these suggested roles.