UC Davis

When an individual honey bee (Apis mellifera) changes in a hive, its’ glandular output also changes. For example, a worker’s mandibular glands (Mdg) typically produce larval food and other pheromones but in queen-less hives it will more closely resemble a queen’s. As the biosynthesis of insect pheromones occurs in specialized tissues and involves regulatory modifications to conserved metabolic pathways, we hypothesized microRNAs (miRs), short (~22 nucleotide) RNA negative transcriptional modifiers and known regulators of metabolic pathways, would have significant roles in regulating pheromone production in honey bee Mdgs. We further hypothesized queen-less workers would have similar miR expression profiles as queens. Small RNA-Seq of the Mdg identified robust caste-specific (queen and worker) miRs profiles as well as a high number of previously undescribed miRs. Worker-expressed genes in the Mdg were enriched for predicted miR response elements (MREs) of miRs coherently up-regulated in both queens and queen-less workers with some ovary activation. In addition, novel worker-expressed genes were enriched for MREs of novel queen-expressed miRs. Predicted miR-protein-protein interaction networks identified potential regulatory hubs and detailed regulatory roles for individual miRs expressed according to caste and mating status. We also found putative worker pheromone biosynthesis genes expressed in queens are enriched for MREs of two worker-expressed miRs; ame-miR-31a-5p and ame-miR-92b-3p. Interestingly the two fatty acid synthase genes that may be expressed according to caste are predicted to contain the highest number of MREs for anti-correlated miRs of all putative pheromone biosynthesis genes. MREs for ame-miR-375-3p that are highly up-regulated in queens and queen-less workers relative to queen-right workers, are enriched in genes down-regulated in queen-less workers relative to queen-right workers. Mandibular gland RNA-sequencing of queen-less worker bees fed an inhibitor for ame-miR-375-3p identified multiple genes involved in metabolic processes, autophagy, and stress responses reverting to the expression profile of a queen-right worker.