Annotation of GST genes in Diaphorina citri

Citrus greening disease, or Huanglongbing (HLB), is a crop blight that has been a great detriment to citrus industries worldwide. HLB is caused by the bacterial pathogen Candidatus Liberibacter asiaticus (CLas), which is transmitted to citrus trees by the insect vector Diaphorina citri (D. citri), the Asian citrus psyllid. To combat this threat, a better understanding of D. citri and CLas interactions is necessary. An important class of enzymes within D. citri are the Glutathione S-transferases (GSTs), which are involved in the detoxification of a variety of chemical substrates, including insecticides. Functional analysis in other insects reveals that a loss-of-function of these genes results in increased susceptibility to certain insecticides. Within the D. citri genome, eighty gene models were putatively identified as GST genes based on results of InterProScan domain classification and gene ontology term analysis. Twenty of these gene models identified as Glutathione S-transferase were annotated using DNA and RNA sequencing data along with computer predicted models in Citrusgreening.org WebApollo. The D. citri GST gene models contained conserved domains characteristic of the GST protein family, including the class Delta and Epsilon subfamily. Both an N-terminal thioredoxin-fold domain and a C-terminal alpha helical domain were also identified. Pairwise sequence analysis of the manually curated GST sequences identified artifact duplications, which were removed. Remaining models had percent identity above 40% and query coverage over 85% compared to other insects. Having high-quality annotated GST gene models is a crucial first step in developing accurate molecular therapeutics for insecticide application against D. citri.