RNA-seq in the honey bee pylorus in response to the gut symbiont Frischella perrara. Apis mellifera carnica

The honey bee is a key pollinator of wild and crop plants and its relatively simple gut microbiota makes it an attractive model to study host-microbiota interactions. Here, we monitored host gene expression in the pylorus of honey bees in response to mono-colonization with the bacterial gut symbiont Frischella perrara which causes the scab phenotype. This phenotype corresponds to a dark brown/black band which was proposed to be a melanization response from the host, which is known to occur in insects following pathogen infection or wounding. Our aim was to characterize the host response to this bacterium and to compare it to that induced by another honey bee microbiota member (Snodgrassela alvi) not causing the phenotype. In addition to bees reared under laboratory conditions, we also compared gene expression in the pylorus between bees sampled from the hive which had the phenotype versus hive bees without the phenotype.This study shows that genes differentially expressed in response to F. perrara are enriched in genes involved in transport and immune processes. In particular, numerous genes of the melanization cascade were significantly upregulated, providing corroborating evidence that the scab phenotype indeed corresponds to a melanization response from the host.