ARS | Publication request: Microarray analysis of gene regulations and potential association with acephate-resistance and fitness cost in Lygus lineola

Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 21, 2012
Publication Date: May 24, 2012
Citation: Zhu, Y., Guo, Z., He, Y., Luttrell, R.G. 2012. Microarray analysis of gene regulations and potential association with acephate-resistance and fitness cost in Lygus lineola. PLoS One. 7(5):e37586.doi:10.137/journal.pone.0037586.

Interpretive Summary: The tarnished plant bug, an economically important pest of cotton, has become increasingly resistant to pyrethroids and organophosphates in recent years. To better understand mechanisms of acephate resistance, biological, biochemical, and molecular experiments were systematically conducted with susceptible (LLS) and acephate-selected (LLR) field strains. Selection of a field population (Lula) with acephate significantly lowed susceptibility by 2.7-fold, coupled with a significant increase of esterase activities by 2-fold. Analysis of 6,688 genes using microarray revealed 662 differentially expressed genes (=2-fold), including 329 up- and 333 down-regulated genes in LLR. Twelve esterase, four cytochrome P450, and one glutathione S-transferase genes (detoxification genes) were significantly up-regulated, and no such genes were down-regulated in LLR. Forty-four vitellogenin and 23 eggshell protein (reproductive) genes were significantly down-regulated, and no such genes were up-regulated in LLR. Thirteen protease (digestive) genes were significantly down-regulated and only 3 protease genes were up-regulated in LLR. Ontology analysis revealed that more than twice the number of catalysis genes and more than 3.6-fold of metabolic genes were up-regulated, respectively, as compared to those down-regulated with the same molecular and biological functions. The large portion of metabolic or catalysis genes with significant up-regulations indicated a substantial increase of catalytic or metabolic detoxification in LLR. Significant decrease in acephate susceptibility, increases of esterase activities and gene expressions, and variable esterase sequences between LLS and LLR consistently demonstrated a major esterase-mediated resistance in LLR. Significant elevation of P450 gene expression and reduced susceptibility to imidacloprid in LLR indicated a concurrent resistance risk that may impact other classes of insecticides, in addition to the organophosphates. This study demonstrated the first association of down-regulations of reproductive- and digestive-related genes with resistance to conventional insecticides, suggesting potential fitness costs that can alter resistance development. The results are significantly valuable in understanding the underlying mechanisms of resistance and are highly desirable for development of resistance management tactics.

Technical Abstract: The tarnished plant bug has become increasingly resistant to organophosphates in recent years. To better understand acephate resistance mechanisms, biological, biochemical, and molecular experiments were systematically conducted with susceptible (LLS) and acephate-selected (LLR) strains. Selection of a field population with acephate significantly increased resistance ratio to 5.9-fold, coupled with a significant increase of esterase activities by 2-fold. Microarray analysis of 6,688 genes revealed 329 up- and 333 down-regulated (=2-fold) genes in LLR. Six esterase, three P450, and one glutathione S-transferase genes were significantly up-regulated, and no such genes were down-regulated in LLR. All vitellogenin and eggshell protein genes were significantly down-regulated in LLR. Thirteen protease genes were significantly down-regulated and only 3 were up-regulated in LLR. More than twice the number of catalysis genes and more than 3.6-fold of metabolic genes were up-regulated, respectively, as compared to those down-regulated with the same molecular and biological functions. The large portion of metabolic or catalysis genes with significant up-regulations indicated a substantial increase of metabolic detoxification in LLR. Significant increase of acephate resistance, increases of esterase activities and gene expressions, and variable esterase sequences between LLS and LLR consistently demonstrated a major esterase-mediated resistance in LLR, which was functionally provable by abolishing the resistance with esterase inhibitors. In addition, significant elevation of P450 gene expression and reduced susceptibility to imidacloprid in LLR indicated a concurrent resistance risk that may impact other classes of insecticides. This study demonstrated the first association of down-regulation of reproductive- and digestive-related genes with resistance to conventional insecticides, suggesting potential fitness costs associated with resistance development. This study shed new light on the understanding of the molecular basis of insecticide resistance, and the information is highly valuable for development of chemical control guidelines and tactics to minimize resistance and cross resistance risks.