Regulation of gene expression under extreme desiccation: hijacking of heat shock regulatory system.

Polypedilum vanderplanki is ? striking and unique example of an insect that can survive almost complete water loss. Its genome and series of dehydration-rehydration transcriptomes, together with the genome of P. nubifer (congeneric desiccation-sensitive midge), were recently released. Here, using series of data reflecting detailed transcriptome changes in the process of anhydrobiosis, as well as developmental series, we have identified hundreds of new genes and have demonstrated that up to 53% of genes undergo alternative splicing (AS) and that AS plays a prominent role in the desiccation response. We have shown that the TCTAGAA DNA motif, which closely resembles the binding motif of the D. melanogaster heat shock transcription activator (HSTF), is significantly enriched in promoter regions of desiccation-induced genes, such as LEA, thioredoxins or trehalose metabolism-related genes in P. vanderplanki, but not in P. nubifer. Unlike desiccation-senseitive P. nubifer, P. vanderplanki exhibits double TCTAGAA sites upstream of the HSTF gene, that is a likely explanation for the much stronger activation of HSTF in P. vanderplanki compared to P. nubifer under desiccation. Thus, our results show that rewiring of the heat shock regulatory system is an important evolutionary mechanism of desiccation adaptation in P. vanderplanki. Overall design: Examination of P. vanderplanki larva transcription changes under dehydration-rehydration cycle