Characterization of trehalose metabolic genes and corresponding enzymatic activities during diapause of Sitodiplosis mosellana

Trehalose plays crucial roles in energy metabolism and stress tolerance in various organisms. The orange wheat blossom midge Sitodiplosis mosellana, a serious pest of wheat worldwide, undergoes long obligatory diapause as a larva to survive harsh temperature extremes in summer and winter. To gain an insight into trehalose function and metabolic mechanism in this process, we measured the content of trehalose and glucose, as well as enzymatic activities of trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP) and soluble trehalase (Treh1) at pre-diapause, diapause and post-diapause larvae of S. mosellana. Trehalose levels greatly increased upon entry into diapause, peaked in low-temperature quiescence phase, and significantly dropped after resumption of development, highly consistent with activity changes of trehalose-synthetic enzymes SmTPS and SmTPP. In marked contrast, the activity of trehalose-degrading SmTreh1 exhibited a completely reversed profile. This profile was in agreement with contents of its product i.e. glucose. Furthermore, deduced amino acid sequences of cloned SmTPS, SmTPPB, SmTPPC, SmTreh1-1 and SmTreh1-2 genes contained all conserved functional domains, motifs and active sites. Expression patterns of these genes were closely correlated with their enzyme activities. These results suggested that coordination of trehalose synthetic and degradation pathways is responsible for diapause-related trehalose accumulation, which may serve as an energy reserve for post-diapause development and a cryoprotectant against cold stress in winter.