Developmental and Caste-specific Expression Patterns of ATP-Binding
Cassette (ABC) Transporters in Honey bees (Apis mellifera)
Abstract
While honey bees play a vital role in global crop production, they face
increasing exposure to xenobiotic chemicals during commercial
pollination. Multidrug-resistance (MDR)-type ATP-binding cassette (ABC)
transporters provide the first line of defense against xenobiotic
chemicals and are upregulated in resistant pest organisms. While
previous studies in bees have focused on the role of metabolic enzymes
in insect detoxification, the presence and function of ABC transporters
across the hive caste system remains largely unexplored. This study
investigated the gene expression profiles of 12 ABC transporters known
to be involved in chemical detoxification in arthropods across ten honey
bee castes and life stages using quantitative real-time PCR. Protein
homology to known MDR transporters in humans and Drosophila was inferred
from BLAST and through phylogenetic analysis. Seven ABC genes that
showed increased gene expression during worker bee development were
identified as MDR-like transporters (AmeABCB1, AmeABCB6, AmeABCC1,
AmeABCC4a-c, AmeABCG1); and their expression levels were further
investigated in reproductive caste members (drone larvae, adult drones,
queen ovaries, and queens). Significant variations were observed in
defense gene expression among all castes suggesting reduced chemical
defense capabilities in queens as evidenced by a dramatically reduced
expression of five MDR-like transporter genes in queen bees relative to
worker eggs: ABCB1 (4-fold), ABCC1 (2-fold), ABCC4a (2-fold), ABCC4b
(3-fold), and ABCC4c (2-fold). Although our findings suggest that drones
and queens are more vulnerable to direct xenobiotic exposure compared to
workers, further research is required to better understand the different
hive members’ responses to chemical threats.