Gene expression analysis of oxidative stress tolerance in the entomopathogenic nematode Heterorhabditis bacteriophora

Abstract

Summary The entomopathogenic nematode (EPN) Heterorhabditis bacteriophora is used as a biological control agent against diverse insect pests. Nematode-based products contain third-stage Dauer juveniles (DJ), which are adapted to long-term survival. Their longevity can be limited by stress conditions during industrial production up to field application. Oxidative stress has been recently reported to have a direct influence on the H. bacteriophora DJ longevity. Thus, understanding mechanisms by which DJ respond to oxidative stress can provide insights to improve DJ longevity. In this study, we carried out a comparative transcriptomic analysis on the early stage of oxidative stress induction (4 h) in two H. bacteriophora inbred lines with contrasting oxidative stress tolerance, HU2-IL1 (stress-tolerant) and PT1-IL1 (stress-sensitive). For assessing the transcriptome, MACE, a versatile RNA-seq variant was applied. Our de novo transcriptome assembly generated more than 20 000 transcripts, from which 10 290 were linked to 9776 different Uniprot accessions. The majority of the annotated transcripts presented high homology to parasitic nematodes within the genus Ancylostoma, whereas homology to the genus Caenorhabditis was negligible. A total of 630 and 461 transcripts were up-regulated (log2 fold-change (FC) ⩾ 2.0) in the stress-sensitive and the stress-tolerant line, respectively. The proportion of down-regulated transcripts was higher for both lines. However, down-regulation in the stress-sensitive line (5207 transcripts) exhibited a larger proportion than in the tolerant line (1844 transcripts), which indicates that targeted suppression of biological processes is also a crucial factor for the survival of H. bacteriophora under oxidative stress. Our global view of the transcriptome remodelling under oxidative stress suggests that the stress-sensitive line fails to maintain vital biological processes in contrast to the tolerant line. Interestingly, both lines activated similar biological processes directly involved in detoxification of reactive oxygen species, indicating that expression changes on transcript isoforms are of high relevance in this context. This study will open ways for the selection of DJ longevity predictor genes and allow the design of molecular markers for the breeding of improved lines.