Comparative genome sequencing reveals genomic signature of extreme desiccation tolerance in the anhydrobiotic midge

Abstract

Anhydrobiosis represents an extreme example of tolerance adaptation to water loss, where an organism can survive in an ametabolic state until water returns. Here we report the first comparative analysis examining the genomic background of extreme desiccation tolerance, which is exclusively found in larvae of the only anhydrobiotic insect, Polypedilum vanderplanki. We compare the genomes of P. vanderplanki and a congeneric desiccation-sensitive midge P. nubifer. We determine that the genome of the anhydrobiotic species specifically contains clusters of multi-copy genes with products that act as molecular shields. In addition, the genome possesses several groups of genes with high similarity to known protective proteins. However, these genes are located in distinct paralogous clusters in the genome apart from the classical orthologues of the corresponding genes shared by both chironomids and other insects. The transcripts of these clustered paralogues contribute to a large majority of the mRNA pool in the desiccating larvae and most likely define successful anhydrobiosis. Comparison of expression patterns of orthologues between two chironomid species provides evidence for the existence of desiccation-specific gene expression systems in P. vanderplanki.

Chironomid Midges (Diptera, Chironomidae) Show Extremely Small Genome Sizes

“…1D) and recover after rehydration (Hinton, 1951, (Gusev et al, 2014). The comparison showed that both species had similar genome sizes and that only a limited set of duplicated gene clusters was related to anhydrobiosis in P. vanderplanki (Gusev et al, 2014). The genome sizes inferred from genome assembly were 104 Mb for P. vanderplanki and 107 Mb for P. nubifer and these values did not differ markedly from the genome sizes measured for these species in the present study, which corresponded to approximately 98 Mb.…”

“…vanderplanki is the only insect species known to achieve anhydrobiosis in a completely dehydrated state (Fig. 1D) and recover after rehydration (Hinton, 1951, (Gusev et al, 2014). The comparison showed that both species had similar genome sizes and that only a limited set of duplicated gene clusters was related to anhydrobiosis in P. vanderplanki (Gusev et al, 2014).…”

Signatures of the evolution of parthenogenesis and cryptobiosis in panagrolaimid nematodes

“…candidates across these species has been mapped to the phylogeny and ancestral states have been deduced with a parsimony approach. Internal nodes are numbered in black (2,3,4,5,6,7,8,9,14). The number of gene families acquired via HGT / lost at each node are peer-reviewed) is the author/funder.…”

“…Cryobionts are frequently also anhydrobiotic, as ice sublimation in very low temperatures can freeze-dry. The mechanistic bases of cryptobiosis have been explored in some species (Aphelenchus nematodes 6 , the chironomid Polypedilum vanderplanki 7 , and the tardigrade Ramazzottius varieornatus and Hybsibius dujardini 8 ) and individual molecular players identified.…”

“…Intrinsically disordered proteins do not adopt a stable secondary structure in solution, and are thought to replace structural water on dehydration. They include the late embryogenesis abundant (LEA)-like proteins 7,9,10 , and peer-reviewed) is the author/funder. All rights reserved.…”