Dehydration-induced tps gene transcripts from an anhydrobiotic nematode contain novel spliced leaders and encode atypical GT-20 family proteins

Abstract

Accumulation of the non-reducing disaccharide trehalose is associated with desiccation tolerance during anhydrobiosis in a number of invertebrates, but there is little information on trehalose biosynthetic genes in these organisms. We have identified two trehalose-6-phosphate synthase (tps) genes in the anhydrobiotic nematode Aphelenchus avenae and determined full length cDNA sequences for both; for comparison, full length tps cDNAs from the model nematode, Caenorhabditis elegans, have also been obtained. The A. avenae genes encode very similar proteins containing the catalytic domain characteristic of the GT-20 family of glycosyltransferases and are most similar to tps-2 of C. elegans; no evidence was found for a gene in A. avenae corresponding to Ce-tps-1. Analysis of A. avenae tps cDNAs revealed several features of interest, including alternative trans-splicing of spliced leader sequences in Aav-tps-1, and four different, novel SL1-related transspliced leaders, which were different to the canonical SL1 sequence found in all other nematodes studied. The latter observation suggests that A. avenae does not comply with the strict evolutionary conservation of SL1 sequences observed in other species. Unusual features were also noted in predicted nematode TPS proteins, which distinguish them from homologues in other higher eukaryotes (plants and insects) and in micro-organisms. Phylogenetic analysis confirmed their membership of the GT-20 glycosyltransferase family, but indicated an accelerated rate of molecular evolution. Furthermore, nematode TPS proteins possess N-and C-terminal domains, which are unrelated to those of other eukaryotes: nematode C-terminal domains, for example, do not contain trehalose-6-phosphate phosphatase-like sequences, as seen in plant and insect homologues. During onset of anhydrobiosis, both tps genes in A. avenae are upregulated, but exposure to cold or increased osmolarity also results in gene induction, although to a lesser extent. Trehalose seems likely therefore to play a role in a number of stress responses in nematodes.

Operon Conservation and the Evolution of trans-Splicing in the Phylum Nematoda

“…These SL1 variants are similar, but not identical, to those recently identified in another tylenchine nematode, A. avenae, where they were found at the 5′ ends of transcripts of the trehalose-6-phosphate synthase genes Av-tps-1 and Av-tps-2 [35]. We note that the other described variant SL, SL1M from M. javanica, also a tylenchine (clade IV) nematode, was identified using a truncated SL1-derived primer in a RT-PCR screen [43].…”

“…While SL2-like sequences have proven to be highly polymorphic, SL1 appears to be largely invariant across the phylum. However, variant SL1 SLs have been described in two tylenchine species, Aphelenchus avenae [35] and Meloidogyne javanica [36] (see Figure 1 for the relationships of all nematode species mentioned) [37,38]. …”

Identification of the trehalose-6-phosphate synthase (tps) gene in desiccation tolerant and intolerant tardigrades

“…This lack of variability is in contrast to what has been found in nematodes, where different forms of the tps gene were found (Pellerone et al 2003;Goyal et al 2005a). The scored low variability could be explained by the fact that the methodology used in this study for tps characterization employed primers designed on a highly conserved region (from bacteria to insects, Lapinski & Tunnacliffe 2003), and therefore it may code for a functionally important residue, and be under strong selective pressure.…”

“…In metazoans, the tps gene has been found in several arthropods (Chen et al 2002;Chung 2008;Clark et al 2009;Xu et al 2009) and desiccation intolerant and tolerant nematodes (Pellerone et al 2003;Goyal et al 2005a). However, its presence in desiccation tolerant animals is not universal, as the tps gene was not found in anhydrobiotic bdelloid rotifers (Lapinski & Tunnacliffe 2003).…”

LEA Proteins During Water Stress: Not Just for Plants Anymore

“…Certainly such dual protection with protein and sugar is not always the case, as exemplified by bdelloid rotifers that do not accumulate protective sugars (41,66). Nevertheless, synthesis of trehalose is well established as one event occurring during acquisition of desiccation tolerance in nematodes (67,68) and other organisms (69). Crowe and colleagues (67,70) reported the compelling observation that unless sufficient time is provided for A. avenae to convert glycogen to trehalose prior to desiccation, the nematode does not survive drying; if conversion to trehalose is accomplished during slow drying, dehydration is survived.…”