Abstract:  【Aim】 Endogenous retroviruses (ERVs) are retrovirus-like elements that have been fixed in the host genome for generations. This study aims to characterize the sequence characteristics and infectious ability of an endogenous retroviral element, PxERV, in the diamondback moth (DBM), Plutella xylostella, which we found during an analysis of its testis transcriptome, so as to provide a basis for addressing the role of ERVs in P. xylostella. 【Methods】 The sequence and structural characteristics of PxERV in the P. xylostella genome were analyzed and identified using bioinformatics methods. The env gene sequence of PxERV was cloned and sequenced. A phylogenetic tree of amino acid sequences coded by env genes and envelope glycoproteins of nucleopolyhedroviruses of insects was constructed using MEGA6 software. The expression levels of env gene in the body and testis of strain G88 of P. xylostella at different developmental stages and the copy numbers of env gene in the adult of strain FZ and the adult and larva of strain G88 of P. xylostella were detected using qPCR technology. The independent replication activity of the PxERV in strain G88 was detected by using CRISPR/Cas9 to mediate the mutation of env gene. 【Results】 PxERV exhibits a structure of LTR-pol-env-LTR. The env gene of PxERV was evolutionarily related to the env genes of the retrotransposon osvaldo in Drosophila buzzatii and the endogenous retrovirus Ted in Trichoplusia ni. The expression level of env gene of PxERV was specifically high in male adult testis of strain G88, and its copy number was lower in strain FZ than in strain G88 and showed no difference among different developmental stages of strain G88. After multiple generations of self-crossing in strain G88, the mutant env gene was gradually reduced in the P. xylostella genome until the wild-type env gene was completely restored. 【Conclusion】 PxERV shows the independent replication activity between generations of P. xylostella, but no independent replication activity in different developmental stages of the same generation of P. xylostella. We assume that PxERV might complete inter-generational infection through the male reproductive system of P. xylostella, with further studies required to address the mechanism associated with its infection.

Key words: Plutella xylostella, genome, endogenous retrovirus, env gene, phylogeny, qPCR