Manual curation and phylogenetic analysis of chitinase family genes in the Asian citrus psyllid, Diaphorina citri

Chitinases are enzymes that digest the polysaccharide polymer chitin. Chitin is a major component of insect exoskeletons, which must be replaced multiple times during growth and development in a process known as molting. Insect genomes usually have multiple chitinase genes, some of which are required for molting and some whose functions are still unknown. Since knockdown of the chitinases required for molting causes high levels of lethality, chitinase genes have drawn interest as targets for RNAi-based pest control methods. The Asian citrus psyllid, Diaphorina citri, carries the bacterium that causes Huanglongbing, also known as citrus greening disease, which is devastating the citrus industry worldwide. We have identified and annotated 12 chitinase family genes from D. citri as part of a community effort to create high quality gene models to facilitate the design of interdictory molecules for pest control. Using predicted protein domain content and phylogenetic analysis, we categorized the D. citri chitinases according to a previously established classification scheme and re-evaluated the classification of chitinases in other hemipterans. In addition to chitinases belonging to known groups, we identified a novel class of chitinases present in D. citri and several related hemipterans that appears to be the result of horizontal gene transfer.