Figure 1.
Analysis of desiccation-induced DTR mRNAs.
(A) Fold change clustering of upregulated (green area) and downregulated (pink area) genes. The very low FCC was discarded because the differential expression was too low. The number of genes (n) in each group is shown. (B) Hierarchical clustering of the 64 highly upregulated genes (blue region in panel A). Red/green column shows log2 expression levels before (–) and after (+) preconditioning, cyan column shows log2 fold changes for the genes indicated on the right. Color codes for the heat map are shown top left. Main branches of the dendrogram are labeled ‘a’ (light gray) and ‘b’ (dark gray, see the text for details). Highlighted genes reside in essential anhydrobiotic pathways shown in the legend with unique color codes, which are consistent in the following figures. (C) The trehalose biosynthesis pathway is upregulated in C. elegans upon desiccation stress. Enzymes that catalyze each reaction are shown with the corresponding differential expression values of their transcripts upon preconditioning. These fold changes are shown in green, red, and blue for upregulation, downregulation, and no change, respectively. Glucose-6-phosphate synthesis from lipids involves several steps; therefore, a dashed arrow is used. Highlighted genes are found in the high FCC (panel B). Glc, Glucose; Glc-6-P, glucose-6-phosphate; Glc-1-P, glucose-1-phosphate; UDP-Glc, UDP-glucose; Tre-6-P, trehalose-6-phosphate; Tre, trehalose.
Figure 2.
Comparison of proteomes upon desiccation.
Overlay of false-colored 2D-DIGE images comparing dauer proteomes before (red) and after (green) preconditioning at 98% RH for 4 days. Yellow spots indicate proteins that do not change distinctively. The major proteins identified in these spots are annotated. The numbered regions are shown in higher magnification in Figures S2C–E. For MLC-1/2 (region 8), the red and green spots were identified as phosphorylated and dephosphorylated proteins, respectively. Region 9 possibly shows another post-translational modification.
Figure 3.
Major pathways involved in desiccation tolerance.
(A) Desiccation sensitivities of various mutants from (B-D) candidate pathways are presented in 4 categories. Genes from high FCC are highlighted according to Figure 1. The subcellular localizations of ROS defense enzymes are shown as c, cytosol; e, extracellular; m, mitochondrion; and p, peroxisome.
Figure 4.
Arachidonic acid is essential for desiccation tolerance.
(A) The major components in the biosynthesis of MUFAs and PUFAs in C. elegans (highlighted according to Figure 1). Type of desaturation is shown in orange for every reaction. Modified from [57,59]. (B) Desiccation sensitivities of FAT mutants in 4 categories. (C) PUFA profiles of preconditioned dauer larvae of wild-type worms and fat mutants. Filled and empty boxes indicate the presence and absence of the PUFA species, respectively. LA, Linoleic acid; ALA, α-linolenic acid; GLA, γ-linolenic acid; SA, stearidonic acid; DGLA, dihomo-γ-linolenic acid; O3AA, ω-3 arachidonic acid; AA, ω-6 arachidonic acid; EPA, eicosapentaenoic acid.
Figure 5.
Novel DTR proteins and putative elements of the hygrosensation pathway involved in desiccation tolerance.
Figure 6.
Suggested model of the main strategies of desiccation tolerance in C.
elegans.
The hypometabolic dauer larva senses a decrease in ambient humidity, perhaps via head neurons, and initiates a desiccation response at different levels. As a result of this, ROS and xenobiotics are eliminated, proteins and membranes are stabilized, and other essential functions are fulfilled. The ametabolic transition (anhydrobiosis) can only succeed under these conditions.