Combined metabolome and transcriptome analysis reveals key components of complete desiccation tolerance in an anhydrobiotic insect

Abstract

Some organisms have evolved a survival strategy to withstand severe dehydration in an ametabolic state, called anhydrobiosis. The only known example of anhydrobiosis among insects is observed in larvae of the chironomid Polypedilum vanderplanki. Recent studies have led to a better understanding of the molecular mechanisms underlying anhydrobiosis and the action of specific protective proteins. However, gene regulation alone cannot explain the rapid biochemical reactions and independent metabolic changes that are expected to sustain anhydrobiosis. For this reason, we conducted a comprehensive comparative metabolome–transcriptome analysis in the larvae. We showed that anhydrobiotic larvae adopt a unique metabolic strategy to cope with complete desiccation and, in particular, to allow recovery after rehydration. We argue that trehalose, previously known for its anhydroprotective properties, plays additional vital roles, providing both the principal source of energy and also the restoration of antioxidant potential via the pentose phosphate pathway during the early stages of rehydration. Thus, larval viability might be directly dependent on the total amount of carbohydrate (glycogen and trehalose). Furthermore, in the anhydrobiotic state, energy is stored as accumulated citrate and adenosine monophosphate, allowing rapid reactivation of the citric acid cycle and mitochondrial activity immediately after rehydration, before glycolysis is fully functional. Other specific adaptations to desiccation include potential antioxidants (e.g., ophthalmic acid) and measures to avoid the accumulation of toxic waste metabolites by converting these to stable and inert counterparts (e.g., xanthurenic acid and allantoin). Finally, we confirmed that these metabolic adaptations correlate with unique organization and expression of the corresponding enzyme genes.

Parallel evolution of trehalose production machinery in anhydrobiotic animals via recurrent gene loss and horizontal transfer

“…figure 2 f ; electronic supplementary material, tables S1 and S2). A recent study indicated that sleeping chironomids also employ trehalose as an energy source for a safe recovery from anhydrobiosis [ 41 ]. The co-occurrence of TPS–TPP acquisition and trehalase gene expansion in Paramacrobiotus sp.…”

Genome-Wide Role of HSF1 in Transcriptional Regulation of Desiccation Tolerance in the Anhydrobiotic Cell Line, Pv11

“…These data demonstrate that HSF1 works as both activator and repressor in Pv11 cells. The repression of cellular process genes is thought also to be important for entering anhydrobiosis in P. vanderplanki , because many metabolic and cellular processes that operate under normal conditions come to a halt in P. vanderplanki larvae and Pv11 during desiccation and trehalose treatment [ 28 , 47 , 54 ]. Although the repression mechanism for such cellular processes has not been yet described, our current results suggest only indirect regulation of the respective genes by HSF1, because HSEs were not enriched in their promoters ( Figure 4 b).…”

Genome-Wide Role of HSF1 in Transcriptional Regulation of Desiccation Tolerance in the Anhydrobiotic Cell Line, Pv11

“…These data demonstrate that HSF1 works as both activator and repressor in Pv11 cells. The repression of cellular process genes is thought also to be important for entering anhydrobiosis in P. vanderplanki, because many metabolic and cellular processes that operate under normal conditions come to a halt in P. vanderplanki larvae and Pv11 during desiccation and trehalose treatment [22,41,49]. Although the repression mechanism for such cellular processes has not been yet described, our current results suggest only indirect regulation of the respective genes by HSF1, because HSEs were not enriched in their promoters (Figure 4b).…”