Identification, genomic organization and expression profiles of four heat shock protein genes in the western flower thrips, Frankliniella occidentalis.

The western flower thrips, Frankliniella occidentalis, is an important invasive pest with a strong tolerance for extreme temperatures; however, the molecular mechanisms that regulate thermotolerance in this insect remain unclear. In this study, four heat shock protein genes were cloned from F. occidentalis and named Fohsp90, Fohsc701, Fohsc702 and Fohsp60. These four Hsps exhibited typical characteristics of heat shock proteins. Subcellular localization signals and phylogenetic analysis indicated that FoHsp90 and FoHsc701 localize to the cytosol, whereas FoHsc702 and FoHsp60 were located in the endoplasmic reticulum and mitochondria, respectively. Analysis of genomic sequences revealed the presence of introns in the four genes (three, four, seven, and five introns for Fohsp90, Fohsc701, Fohsc702 and Fohsp60, respectively). Both the number and position of introns in these four genes were quite different from analogous genes in other species. qRT-PCR indicated that the four Fohsps were detected in second-stage larvae, one-day-old pupae, and one-day-old adults, and mRNA expression levels were lowest in larvae and highest in pupae. Fohsc701 and Fohsc702 possessed similar expression patterns and were not induced by cold or heat stress. Expression of Fohsp60 was significantly elevated by heat, and Fohsp90 was rapidly up-regulated after exposure to both cold and heat stress. Exposure to -8°C had no effect on expression of the four Fohsps; however, expression of Fohsp90 and Fohsp60 was highest after a 2-h incubation at 39°C. Furthermore, cold and heat hardening led to significant up-regulation of the four Fohsps compared to their respective controls. Collectively, our results indicate that the four FoHsps contribute to insect development and also function in rapid cold or heat hardening; furthermore, FoHsp90 and FoHsp60 contribute to thermotolerance in F. occidentalis.