Transcriptome-Based Identification of ABC Transporters in the Western Tarnished Plant Bug Lygus hesperus

J Joe Hull,Scott M Geib,Kendrick Chaney,Laura Corley Lavine,Colin S Brent,Douglas Walsh,Jeffrey A Fabrick,Youjun Zhang

doi:10.1371/journal.pone.0113046

Abstract

ATP-binding cassette (ABC) transporters are a large superfamily of proteins that mediate diverse physiological functions by coupling ATP hydrolysis with substrate transport across lipid membranes. In insects, these proteins play roles in metabolism, development, eye pigmentation, and xenobiotic clearance. While ABC transporters have been extensively studied in vertebrates, less is known concerning this superfamily in insects, particularly hemipteran pests. We used RNA-Seq transcriptome sequencing to identify 65 putative ABC transporter sequences (including 36 full-length sequences) from the eight ABC subfamilies in the western tarnished plant bug (Lygus hesperus), a polyphagous agricultural pest. Phylogenetic analyses revealed clear orthologous relationships with ABC transporters linked to insecticide/xenobiotic clearance and indicated lineage specific expansion of the L. hesperus ABCG and ABCH subfamilies. The transcriptional profile of 13 LhABCs representative of the ABCA, ABCB, ABCC, ABCG, and ABCH subfamilies was examined across L. hesperus development and within sex-specific adult tissues. All of the transcripts were amplified from both reproductively immature and mature adults and all but LhABCA8 were expressed to some degree in eggs. Expression of LhABCA8 was spatially localized to the testis and temporally timed with male reproductive development, suggesting a potential role in sexual maturation and/or spermatozoa protection. Elevated expression of LhABCC5 in Malpighian tubules suggests a possible role in xenobiotic clearance. Our results provide the first transcriptome-wide analysis of ABC transporters in an agriculturally important hemipteran pest and, because ABC transporters are known to be important mediators of insecticidal resistance, will provide the basis for future biochemical and toxicological studies on the role of this protein family in insecticide resistance in Lygus species.

Highlights

ATP-binding cassette (ABC) proteins are an extensive family of transmembrane proteins that are ubiquitous to all organisms
Because some ABC transporters are associated with cellular stress [53,54,55,56,57], we combined the transcriptomes of L. hesperus exposed to cold and heat stress as well as nonstressed cohorts
We identified 12 ABCC-like transcripts in L. hesperus, a number comparable to that reported for other arthropods with the exception of T. urticae, T. castaneum, and C. populi, all of which have undergone significant expansion of the ABCC subfamily (Table 1)

Summary

Introduction

ATP-binding cassette (ABC) proteins are an extensive family of transmembrane proteins that are ubiquitous to all organisms. The NBDs, which are critical for ATP-binding and hydrolysis, provide the energy necessary for driving a substrate across the membrane They are characterized by a catalytic core comprised of a Walker A motif (GXXGXGKS/ T) and a Walker B motif (QQQQD; where Q represents a hydrophobic residue) separated by a conserved Q-loop and a Walker C motif. This latter component is a structurally diverse helical segment encompassing the ABC signature sequence (LSGGQ) that distinguishes ABC transporter family members from other ATP-binding proteins. The ABC transporter domains are organized as either full-transporters (FT) containing four domains (2 TMDs and 2 NBDs) or halftransporters (HT) comprised of only two domains (1 TMD and NBD) that require homo- or heterodimerization for full functionality [2,3]

Methods

Results

Conclusion