Differential gene expression between hygienic and non-hygienic honeybee (Apis mellifera L.) hives

Abstract

Background: Hygienic behavior is a complex, genetically-based quantitative trait that serves as a key defense mechanism against parasites and diseases in Apis mellifera. Yet, the genomic basis and functional pathways involved in the initiation of this behavior are still unclear. Deciphering the genomic basis of hygienic behavior is a prerequisite to developing an extensive repertoire of genetic markers associated to the performance level of this quantitative trait. To fill this knowledge gap, we performed an RNA-seq on brain samples of 25 honeybees per hives from five hygienic and three non-hygienic hives.

Results: This analysis revealed that a limited number of functional genes are involved in honeybee hygienic behavior. The genes identified, and especially their location in the honeybee genome, are consistent with previous findings. Indeed, the genomic sequences of most differentially expressed genes were found on the majority of the QTL regions associated to the hygienic behavior described in previous studies. According to the Gene Ontology annotation, 15 genes are linked to the GO-terms DNA or nucleotide binding, indicating a possible role of these genes in transcription regulation. Furthermore, GO-category enrichment analysis revealed that electron carrier activity is over-represented, involving only genes belonging to the cytochrome P450. Cytochrome P450 enzymes' overexpression can be explained by a disturbance in the regulation of expression induced by changes in transcription regulation or sensitivity to xenobiotics. Over-expressed cytochrome P450 enzymes could potentially degrade the odorant pheromones or chemicals that normally signal the presence of a diseased brood before activation of the removal process thereby inhibit hygienic behavior.

Conclusions: These findings improve our understanding on the genetics basis of the hygienic behavior. Our results show that hygienic behavior relies on a limited set of genes linked to different regulation patterns (expression level and biological processes) associated with an over-expression of cytochrome P450 genes.

Fig. 1

Volcano plot for honeybee data set. Volcano plot for the 11169 genes from the honeybee data. The x-axis is the fold-change value and the y axis is the - log10 p-value. Using the p-value 0.05 as the threshold cutoff, 96 genes in the upper left and upper right are selected. Red spots indicate the statistically significant DEGs

Fig. 2

Chromosomal position of the DEGs on the Apis mellifera genome. Red spots indicate a gene over-expressed on non-hygienic bees and; green spots indicate an under-expression in non-hygienic bees

Fig. 3

Multi-level pie chart of the major GO-categories represented in the DEG dataset. Panel a represented the GOterm associated to molecular function, Panel b represented the GO-term associated to cellular component andPanel c represented the GO-term associated to biological process