Molecular characterization and tissue expression analysis of five genes for chitinase in the red palm weevil, Rhynchophorus ferrugineus (Coleoptera: Curculionidae)

Abstract

Insect chitinases are hydrolytic enzymes that cleave chitin of the cuticle and peritrophic membrane during molting. Multiple genes encode insect chitinases, which are characterized as having diverse chemical and enzymatic properties depending on the time and the site of expression. This work was done to isolate and characterize chitinase genes from the red palm weevil (RPW), Rhynchophorus ferrugineus (Oliver), a cryptic pest of many palm trees. The isolated five genes were phylogenetically clustered into five different groups (I, II, III, VI, and VII) of the glycoside hydrolase family 18 (GH18). Domain structure analysis revealed that RfCht1 (group I), RfCht3 (group VI), and RfCht5 (group VII) each retained a single catalytic domain of the GH18, whereas RfCht2 (group III)) and RfCht4 (group II) possessed two and five GH18 catalytic domains, respectively. RfCht1, RfCht2, and RfCht3 each retained a single chitin-binding domain (CBD) and RfCht4 retained five CBDs, but RfCht5 lacked CBD. Developmental and tissue expression profiles showed high levels of transcripts of the five genes in the newly hatched first instar larvae. RfCht1 and RfCht2 transcripts were expressed constitutively almost with high levels in young and mature eggs, in all tested larval instars, pre-pupae, pharate pupae, and adults; whereas RfCht3 and RfCht5 transcripts were expressed as low levels in the early instars larvae few hours before molting. In late developmental stages and mature eggs, RfCht3, RfCht4, and RfCht5 were expressed as low levels mainly in the cuticle. This study presents the first report on chitinase genes in the RPW and suggests that these genes have additional roles in the weevil development, which require further elucidation. Key words: Chitinase, conserved motifs, cuticle, domain structure, expression profile, Rhynchophorus ferrugineus