Expression of different desiccation-tolerance related genes in various species of entomopathogenic nematodes

Entomopathogenic nematodes used as biological control agents encounter various stress conditions during extended periods in the soil. We investigated gene expression in nematodes that were tolerant or susceptible to desiccation stress to determine whether enhanced tolerance in these populations results from a 'gene-expression response' to desiccation or if, for enhanced tolerance, no such response is needed, perhaps due to a state of constant 'readiness'. The expressions of four genes, aldehyde dehydrogenase, nucleosome assembly protein 1, glutathione peroxidase and heat-shock protein 40, were characterized during desiccation stress in five entomopathogenic nematode species with differing stress tolerance: Steinernema feltiae strain IS-6, S. feltiae Carmiel strain, Steinernema carpocapsae Mexican strain, Steinernema riobrave, and Heterorhabditis bacteriophora strain TTO1. After 24h of desiccation, we observed an inverse relationship between expression of the studied genes and phenotypic desiccation-tolerance capability in the nematodes. H. bacteriophora TTO1 was most susceptible to desiccation but showed the highest expression of all studied genes under desiccation. S. carpocapsae Mexican strain and S. riobrave showed the lowest expression of these genes but were most tolerant to desiccation. Our study showed no induction of gene expression in stress-tolerant nematodes, whereas the stress-susceptible nematodes responded to stress by induced expression of these genes. Since the different levels of gene expression were found to be related to the different stress-tolerance capabilities of the nematodes, these gene-expression ratios can potentially be used as markers of desiccation tolerance in entomopathogenic nematodes.