Differential Expression of Major Royal Jelly Proteins in the Hypopharyngeal Glands of the Honeybee <em>Apis mellifera</em> upon Bacterial Ingestion

Honeybee vitellogenin (Vg) transports pathogen fragments from the gut to the hypopharyngeal glands and is also used by nurse bees to synthesize royal jelly (RJ), which serves as a vehicle for transferring pathogen fragments to the queen and young larvae. The proteomic profile of RJ from bacterial-challenged and control colonies was compared using mass spectrometry; however, the expression changes of major royal jelly proteins (MRJPs) in hypopharyngeal glands of the honeybee <i>Apis mellifera</i> in response to bacterial ingestion is not well-characterized. In this study, we investigated the expression patterns of <i>Vg</i> in the fat body and <i>MRJPs 1–7</i> in the hypopharyngeal glands of nurse bees after feeding them live or heat-killed <i>Paenibacillus larvae</i>. The expression levels of <i>MRJPs</i> and <i>defensin-1</i> in the hypopharyngeal glands were upregulated along with <i>Vg</i> in the fat body of nurse bees fed with live or heat-killed <i>P. larvae</i> over 12 h or 24 h. We observed that the expression patterns of <i>MRJPs</i> and <i>defensin-1</i> in the hypopharyngeal glands and <i>Vg</i> in the fat body of nurse bees upon bacterial ingestion were differentially expressed depending on the bacterial status and the time since bacterial ingestion. In addition, the <i>AMP</i> genes had increased expression in young larvae fed heat-killed <i>P. larvae</i>. Thus, our findings indicate that bacterial ingestion upregulates the transcriptional expression of <i>MRJPs</i> in the hypopharyngeal glands as well as <i>Vg</i> in the fat body of <i>A. mellifera</i> nurse bees.