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HSP90 is a highly conserved molecule across all species, from bacteria to humans. It plays critical roles in the development, survival, chaperone function, cell cycle control, oncogenic transformation and also in response to abiotic stresses as heat or cold, or the presence of heavy metals. Little is known about biochemical and molecular responses to cold and heat stresses in entomopathogenic nematodes (EPN). In the present study, the isolation and the molecular characterization of the partial cDNA of the hsp-90 and its corresponding gene from the entomopathogenic nematode Heterorhabditis bacteriophora are reported. Four cDNA variants of the Hb-hsp-90 gene were isolated and sequenced. The unexpected finding of intron presence-absence in the Hb-hsp-90 genes of H. bacteriophora opens some questions about their function and their evolutionary significance.

The hsp-90 represents one of the most abundant and evolutionarily conserved proteins that are present in a wide range of organisms from bacteria to humans, functioning both as molecular chaperones and stress proteins. Nematodes are among the most successful organisms in withstanding stress conditions. Little is known about biochemical and molecular events underpinning entomopathogenic nematode responses to environmental stresses, in particular cold and heat stresses. In this study, we report the isolation and molecular characterization of the full-length cDNA of hsp-90 and its correspondlng gene from the entomopathogenic nematodes Heterorhabdltis bacteriophora. Sequencing analyses of several cDNA and genomic clones revealed the presence of different transcripts and genes. The unexpected finding of intron presence-absence in the hsp-90 genes of H. bacteriophora opens some questions about their functlon and their evolutionary significance. Further investigations are ongoing in order to assess the function of the different transcripts in response to different temperature stresses.

A portion of the hsp-90 gene was amplified, using degenerate primers, in Steinernema thesami, S. tbilisiensis and Steinernema sp. isolated in Georgia. Two amplified products were obtained for each species and both fragments were cloned and sequenced. Blast search at NCBI revealed that both fragments for each species coded for hsp-90. Sequence analyses revealed that all three Steinernema species contained two different hsp-90 genes and the main difference was the intron presence-absence between hsp-90 genes. The hsp-9o genes containing introns showed conserved intron position between them with high sequence variation. This study showed, for the first time, the presence of two different isoforms for the hsp-90 in nematodes and the conserved position of the intron between the three Steinernema species. Further investigations are ongoing in order to characterize thermotolerant strains.