Identification And Functional Analysis Of Peroxiredoxin Genes In The Diamondback Moth, Plutella Xylostella (L.)

Peroxiredoxins (Prxs) are part of the family of antioxidant enzymes and are essential for both eukaryotes and prokaryotes. Prxs have been reported in many insects, but not completely in Plutella xylostella.In this study, we have cloned four peroxiredoxins from P. xylostella, which were named PxPrx1, PxPrx3, PxPrx5 and PxPrx6. PxPrx1 and PxPrx3 were typical 2-Cys Prxs, while PxPrx5 was a 2-Cys Prxs and PxPrx6 a 1-Cys Prxs. Phylogenetic analysis showed that PxPrxs are closely related to the Prxs of other insects.The mRNA levels of peroxiredoxins at different developmental stages of P. xylostella were evaluated by the quantitative real time PCR (qRT-PCR). The results showed that PxPrx1 and PxPrx5 both had a high level of expression in pupae and adults. PxPrx3 had a high level of expression in larvae and adults, and low in pupae. PxPrx6 was expressed at a high level in adults. Comparisons of the peroxiredoxin expression levels in the 3rd instar larvae of three strains of P. xylostella showed that the two insecticide resistant strains had higher expression of PxPrx1 that the susceptible strain while the other Prx did not vary in expression levels. The results showed PxPrx1, PxPrx6 and PxPrx5 were highly expressed in Malpighian tubules but not in midgut, head, epidermis, and fat body. PxPrx3 did not show significantly difference in expression in these tissues. In general, PxPrx6 had lower expression level than the other three genes which were at similar levels.In this study, we also found that the expression levels of four peroxiredoxin genes varied when exposed to abiotic stresses, such as cold, heat, UV, H2O2 and insecticide treatments. PxPrx3 and PxPrx5 were selected for RNAi because of their specific expression. The expression level of two genes was significantly inhibited after 24 h with the injection of dsRNA. After UV treatment for 2 h on DBM larvae, the expression level of PxPrx3 in the group that was injected with dsGFP was higher than the control group and the group injected with dsPxPrx3. The expression level of PxPrx5 in the group injected with dsGFP was lower than control group. After heat treatment for 2 h, DBM larvae injected with dsPxPrx3 had a higher expression level of PxPrx3 than the control group and the group of injected with dsGFP. The expression level of PxPrx5 in the group injected with dsGFP was lower than control group.Thus, PxPrxs can protect P. xylostella against oxidative damage to a certain extent, but the transcriptional regulation level of PxPrxs was variable, which depended on the type of PxPrxs and stress intensity.