Abstract

Laccases, member of multicopper oxidase (MCO) family enzymes, play crucial roles in insects’ cuticle tanning and pigmentation. The purpose of this study was to identify and characterize a laccase gene from the red palm weevil (RPW), Rhynchophorus ferrugineus. The isolated RPW laccase gene sequence was 3,389 bp, including a 2,163 bp open reading frame that encodes 720 amino acids. The RPW laccase gene conserved the MCO functional motifs Type-3, Type-1, and Type-2, respectively. Phylogenetic analysis categorized this protein into the functional cluster 2 of insect laccases (Lac2). The primary transcripts for R. ferrugineus laccase 2 (RfeLac2) were highly expressed in the adult’s cuticle, elytra, and hindwings, and in the larval cuticles four days before molting. Then, the transcripts were declined drastically in the larval cuticles three days before molting. This implies that the suppression of RfeLac2 in the larvae occurs earlier than expected. RfeLac2 transcripts were very low in the gut and adipose tissues of larvae and adults, irrespective to the span to undergo molting. This suggests that RfeLac2 is not active in the tissues that do not undergo heavy sclerotization. Three-dimensional (3-D) structure modeling of RfeLac2 predicted eight histidines, one glycine, and one phenylalanine, as copper-binding ligands on the laccase active center. The study finding indicates that the pattern of the RPW RfeLac2 expression varies from other coleopteran insects, a phenomenon that requires further investigation.

Key words: Cuticle, expression, laccase, phylogeny, Red palm weevil.