Desiccation and rehydration elicit distinct heat shock protein transcript responses in flesh fly pupae

Heat shock proteins (Hsps) are a ubiquitous component of the cellular response to stress in both prokaryotic and eukaryotic organisms, but their role and function during desiccation stress in terrestrial arthropods has received limited attention. Molecular responses to rehydration are arguably as important as those to desiccation in maintaining cellular integrity and enzyme activity, but the role of Hsps during stress recovery is poorly understood and has never been addressed with respect to rehydration in insects. This study identifies distinct differences in the Hsp response to desiccation and rehydration in the flesh fly Sarcophaga crassipalpis, as well as differences in the desiccation responses of diapausing and nondiapausing pupae. In nondiapausing pupae, the expression of two inducible Hsps (Hsp23 and Hsp70) is upregulated by desiccation, but the water loss threshold for Hsp expression changes at different rates of dehydration. Continued desiccation results in the prolonged expression of both Hsp23 and Hsp70, which may contribute to the delayed adult eclosion noted in samples desiccated for more than 3 days at <5% relative humidity/25degreesC. In diapausing pupae, hsp23 and hsp70 transcripts are already highly expressed and are not further upregulated by desiccation stress. Both of the constitutive Hsps investigated, Hsp90 and Hsc70, were unresponsive to desiccation in both nondiapausing and diapausing pupae. However, both Hsp90 and Hsc70 were upregulated upon rehydration in nondiapausing and diapausing pupae. These results indicate distinct roles for the different Hsps during desiccation stress and rehydration/stress recovery. The response to desiccation recovery (rehydration) is similar to the Hsp response to cold recovery identified in S. crassipalpis: Hsp90 and Hsc70 are upregulated in both cases.