Abstract
Secretions from mandibular glands (MGs) have important caste-specific functions that are associated with the social evolution of honey bees. To gain insights into the molecular architecture underlying these caste differences, we compared the gene expression patterns of MGs from queens, queenright workers (WQRs) and queenless workers (WQLs) using high-throughput RNA-sequencing technology. In total, we identified 46 candidate genes associated with caste-specific biosynthesis of fatty acid pheromones in the MG, including members of cytochrome P450 (CYP450) family and genes involved in fatty acid β-oxidation and ω-oxidation. For further identification of the CYP450s genes involved in the biosynthesis of MG secretions, we analyzed by means of qPCR, the expression levels of six of the CYP450 genes most abundantly expressed in the transcriptome analysis across different castes, ages, tasks and tissues. Our analysis revealed that CYP6AS8 and CYP6AS11, the most abundantly expressed CYP450 genes in worker and queen MGs, respectively, are selectively expressed in the MGs of workers and queens compared to other tissues. These results suggest that these genes might be responsible for the critical bifurcated hydroxylation process in the biosynthesis pathway. Our study contributes to the description of the molecular basis for the biosynthesis of fatty acid-derived pheromones in the MGs.
Highlights
Reproductive division of labor in social insects is often associated with phenotypic plasticity, whereby a single genome expresses different phenotypes with marked differences in reproduction and morphology in response to environmental cues[1]
A major physiological differences between honey bee queen mandibular glands (MGs) and worker MGs relies on the function, which develop in both castes but serve different functions[3]: In queens, MGs are responsible for the production of queen mandibular pheromone (QMP), which mainly consists of two ω-1-hydroxylated decenoic acids (9-oxo-2-decenoic acid (9-ODA) and 9-hydroxy-2-decenoic acid (9-HDA) and two aromatic components[4]
Our results revealed the global gene expression pattern of honey bee MGs, with approximately 10000 genes being detected
Summary
Reproductive division of labor in social insects is often associated with phenotypic plasticity, whereby a single genome expresses different phenotypes with marked differences in reproduction and morphology in response to environmental cues[1]. One of the most fascinating examples of differential gene expression associated with organ plasticity in social insects is the caste-specific difference in the biosynthesis of pheromones in honey bee mandibular glands (MGs). Malka et al presented the first global gene expression analysis of honey bee MGs from virgin queens and three types of workers using microarray analysis[20]. These studies offer the first demonstrations of genes regulating primer pheromone biosynthesis in the honey bee, and demonstrated that MG gene expression is influenced by caste, social environment and reproductive physiology. The important regulatory genes involved in the biosynthesis of fatty acid-derived pheromones remain to be identified
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