Proteomic analysis in the Dufour's gland of Africanized Apis mellifera workers (Hymenoptera: Apidae)

Post-transcriptional regulation of Dufour's gland reproductive signals in bumble bees

Pheromone communication is a key mechanism by which the reproductive division of labor is maintained within insect communities. Understanding how pheromones evolved to regulate social behavior requires knowledge of the molecular regulation of their production. However, even in cases where pheromones were identified, our understanding of their biosynthesis and molecular regulation remains limited. Bumble bees provide a unique system to explore pheromone biosynthesis since workers produce ester sterility signals in their Dufour's gland that differ from gyne-specific esters and are not produced by queens. These esters are hypothesized to be produced in the exocrine gland where they are stored, and indeed queens, gynes and workers differ significantly in the expression of Dufour's gland genes coding to enzymes involved in the biosynthesis of esters. However, a previous transcriptome analysis revealed no gene expression differences in the Dufour's gland of workers despite differences in both ester production and ovarian activation, suggesting that ester production may be regulated lower down. Proteomics of the Dufour's gland of queens, gynes, and workers recovered over 2400 proteins and broadly matched the previous RNAseq data. However, more than 100 differentially expressed proteins were found between the worker groups, including key enzymes in fatty acid biosynthesis, indicating that the regulation of reproductive signal biosynthesis in workers is done post-transcription. Overall, our data provide evidence that pheromone biosynthesis in the Dufour's gland is caste specific, that gynes and workers are likely using different enzymes to make their respective wax esters, and that the regulation on pheromone production in queens, gynes and workers is likely done at different regulatory levels, with workers signals being subjected to regulation at the protein level.

Identification of low-abundance proteins in the royal jelly using the Osborne classification method

Royal jelly (RJ) is recognized as healthy food, with a high content of proteins. These proteins play important roles in honeybee caste and human health, but the proteomic analysis of low-abundance proteins in RJ has long been a challenge. Herein, we used the Osborne classification method to separate the RJ proteins of Xinjiang black bees into various fractions. The globulin, ethanol-soluble protein, and glutelin fractions were further separated by SDS-PAGE, and proteomic analysis was carried out by LC-MS/MS and searched against the UniProt database. A total of 23 secretory proteins were identified by proteomic analysis, in which 7 proteins were identified for the first time in RJ. The Osborne classification method combining one-dimensional gel electrophoresis-based proteomic analysis allows the identification of low-abundance proteins in the RJ and greatly extends the knowledge about the components and functions of RJ proteins. The raw data are available via ProteomeXchange with the identifier PXD023315. SIGNIFICANCE: This study makes an important contribution to the research of the components and functions of low-abundance royal jelly proteins for the following reasons.

Pine defense against eggs of an herbivorous sawfly is elicited by an annexin-like protein present in egg-associated secretion

Known elicitors of plant defenses against eggs of herbivorous insects are low-molecular-weight organic compounds associated with the eggs. However, previous studies provided evidence that also proteinaceous compounds present in secretion associated with eggs of the herbivorous sawfly Diprion pini can elicit defensive responses in  Pinus sylvestris. Pine responses induced by the proteinaceous secretion are known to result in enhanced emission of (E)-β-farnesene, which attracts egg parasitoids killing the eggs. Here, we aimed to identify the defense-eliciting protein and elucidate its function. After isolating the defense-eliciting protein from D. pini egg-associated secretion by ultrafiltration and gel electrophoresis, we identified it by MALDI-TOF mass spectrometry as an annexin-like protein, which we named 'diprionin'. Further GC-MS analyses showed that pine needles treated with heterologously expressed diprionin released enhanced quantities of (E)-β-farnesene. Our bioassays confirmed attractiveness of diprionin-treated pine to egg parasitoids. Expression of several pine candidate genes involved in terpene biosynthesis and regulation of ROS homeostasis was similarly affected by diprionin and natural sawfly egg deposition. However, the two treatments had different effects on expression of pathogenesis-related genes (PR1, PR5). Diprionin is the first egg-associated proteinaceous elicitor of indirect plant defense against insect eggs described so far.