Transcriptomic comparison of thiamethoxam-resistance adaptation in resistant and susceptible strains of Aphis gossypii Glover.

A thiamethoxam-resistant strain of cotton aphid (ThR) strain displayed a 19.35-fold greater resistance to thiamethoxam compared to a susceptible cotton aphid (SS) strain. Solexa sequencing technology was used to investigate differentially expressed genes (DEGs) in cotton aphids in the context of thiamethoxam resistance. A total of 22,569,311 and 21,317,732 clean reads were obtained from the ThR and SS transcriptomes, respectively, and assembled into 35,222 non-redundant (Nr) consensus sequences. The expression of 620 unigenes changed significantly in the ThR libraries compared to the SS strain; 349 genes were up-regulated, and 271 genes were down-regulated (P≤0.001). Expression levels of ribosomal proteins, ATP synthase, cytochrome c oxidase, ecdysteroid UDP-glucosyltransferase and esterase were up-regulated significantly in the ThR strain compared to the SS strain. The genes of cuticle proteins, salivary proteins, and fibroin heavy chain decreased dramatically. One nicotinic acetylcholine receptor (nAChR) α subunit was down-regulated in the ThR strain. The expression levels of 10 differentially expressed unigenes were confirmed using real-time RT-PCR, and the observed trends in gene expression matched the Solexa expression profiles. Specific single-nucleotide polymorphisms (SNPs) in nAChRs that cause amino acid substitution were found from the ThR and SS stains respectively. These data illustrate that genetic changes in nAChR genes and up-regulated ribosomal proteins, ecdysteroid UDP-glucosyltransferase, cytochrome c oxidase, esterase and peroxidase may confer the tolerance of resistant cotton aphids to thiamethoxam.