Molecular characterization, expression pattern and metabolic activity of flavin-dependent monooxygenases in Spodoptera exigua

Molecular identification, expression and function analysis of peroxidasin in Chilo suppressalis

Peroxidasin plays a unique role in the formation and stability of extracellular matrix (ECM) in the animal kingdom; however, it was only characterized in Diptera, not in other insect orders. In this study peroxidasin (CsPxd) was first identified and characterized from Chilo suppressalis, a lepidopteran pest. CsPxd complementary DNA with a 4080 bp open reading frame encodes a peptide of 1359 amino acids; the derived amino acid sequence of CsPxd harbors the typical structural characteristics of peroxidasin family in heme-peroxidase superfamily, including the signal peptide at N-terminal, leucine-rich repeat domain, Ig-loop motifs and peroxidase domain, signifying the extracellular location of protein and the involvement in ECM formation. Eukaryotic expression reveals CsPxd protein displays peroxidase activity on H2 O2 , justifying the membership of peroxidase. Phyletic analysis shows the monophyletic evolution pattern of peroxidasin in insect phyle, and moreover only one peroxidasin is present in each species of insects, suggesting its evolutionary conservation on function. Peroxidasin messenger RNA is mainly expressed in egg and the final instar larvae stage. Injection of peroxidasin double-stranded RNA into the final instar larvae impacts the cuticle sclerotization during the metamorphosis from larvae to pupa, and eventually lead to lethality of larvae and pupa. These results suggest the presence of collagen crosslink in chorion and cuticle of insects, and indicate peroxidasin plays a role in the development of chorion and cuticle; furthermore peroxidasin might be the one of potential target genes for pest control using RNA interference.

A flavin-dependent monooxgenase confers resistance to chlorantraniliprole in the diamondback moth, Plutella xylostella

The diamondback moth, Plutella xylostella, is a damaging pest of cruciferous crops, and has evolved resistance to many of the insecticides used for control, including members of the diamide class. Previous work on the molecular basis of resistance to diamides has documented mutations in the target-site, the ryanodine receptor, in resistant populations of P. xylostella worldwide. In contrast the role of metabolic resistance to this insecticide class is significantly less clear. Here we show that overexpression of a flavin-dependent monooxgenase (FMO) confers resistance to the diamide chlorantraniliprole in P. xylostella. Transcriptome profiling of diamide resistant strains, with and without target-site resistance, revealed constitutive over-expression of several transcripts encoding detoxification enzymes compared to susceptible strains. Two of these, CYP6BG1, and PxFMO2 were particularly highly overexpressed (33,000 and 14,700-fold, respectively) in a resistant strain (HAW) lacking target-site resistance. After 17 generations without diamide selection the resistance of the HAW strain fell by 52-fold and the expression of PxFMO2 by > 1300-fold, however, the expression of CYP6BG1 declined by only 3-fold. Generation of transgenic Drosophila melanogaster expressing these genes demonstrated that PxFMO2, but not CYP6BG1, confers resistance in vivo. Overexpression of PxFMO2 in the HAW strain is associated with mutations, including a putative transposable element insertion, in the promoter of this gene. These enhance the expression of a reporter gene when expressed in a lepidopteran cell line suggesting they are, at least in part, responsible for the overexpression of PxFMO2 in the resistant strain. Our results provide new evidence that insect FMOs can be recruited to provide resistance to synthetic insecticides.