Abstract
BackgroundPreviously, we described the heat shock response in dipteran species belonging to the family Stratiomyidae that develop in thermally and chemically contrasting habitats including highly aggressive ones. Although all species studied exhibit high constitutive levels of Hsp70 accompanied by exceptionally high thermotolerance, we also detected characteristic interspecies differences in heat shock protein (Hsp) expression and survival after severe heat shock. Here, we analyzed genomic libraries from two Stratiomyidae species from thermally and chemically contrasting habitats and determined the structure and organization of their hsp70 clusters.ResultsAlthough the genomes of both species contain similar numbers of hsp70 genes, the spatial distribution of hsp70 copies differs characteristically. In a population of the eurytopic species Stratiomys singularior, which exists in thermally variable and chemically aggressive (hypersaline) conditions, the hsp70 copies form a tight cluster with approximately equal intergenic distances. In contrast, in a population of the stenotopic Oxycera pardalina that dwells in a stable cold spring, we did not find hsp70 copies in tandem orientation. In this species, the distance between individual hsp70 copies in the genome is very large, if they are linked at all. In O. pardalina we detected the hsp68 gene located next to a hsp70 copy in tandem orientation. Although the hsp70 coding sequences of S. singularior are highly homogenized via conversion, the structure and general arrangement of the hsp70 clusters are highly polymorphic, including gross aberrations, various deletions in intergenic regions, and insertion of incomplete Mariner transposons in close vicinity to the 3'-UTRs.ConclusionsThe hsp70 gene families in S. singularior and O. pardalina evolved quite differently from one another. We demonstrated clear evidence of homogenizing gene conversion in the S. singularior hsp70 genes, which form tight clusters in this species. In the case of the other species, O. pardalina, we found no clear trace of concerted evolution for the dispersed hsp70 genes. Furthermore, in the latter species we detected hsp70 pseudogenes, representing a hallmark of the birth-and-death process.
Highlights
We described the heat shock response in dipteran species belonging to the family Stratiomyidae that develop in thermally and chemically contrasting habitats including highly aggressive ones
Hsp70 copies in S. singularior cluster are subject to gross rearrangement, and their order in most phages is S2, S3 and S4, in phages 33 and the S5 gene is located after S3, while in phage an inverted pair is formed by S1 and S3 genes (Figure 1A)
The hsp70 copy number does not differ significantly between less tolerant O. pardalina and more thermotolerant S. singularior, the general organization of hsp70 genes is divergent in these two species
Summary
We described the heat shock response in dipteran species belonging to the family Stratiomyidae that develop in thermally and chemically contrasting habitats including highly aggressive ones. It is noteworthy that the predominant fraction of investigations on the stress response have largely (but not entirely) been previously performed on a small number of model organisms in the laboratory and, have limited value in an ecological context Keeping this in mind we usually included in our investigation related species or geographical strains from nature, in particular those inhabiting biotopes or regions with strikingly contrasting average temperatures [8,11,12,13,14]. Long-term and large-scale studies of the Hsps gene system in species and geographical strains that differ in the temperature of habitats, performed in various laboratories, have disclosed a few basic patterns in the functioning and evolution of this system in organisms living under adverse conditions [4,5,11,15,16,17]
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