Abstract
The disaccharide sugar trehalose is essential for desiccation resistance in most metazoans that survive dryness; however, neither trehalose nor the enzymes involved in its metabolism have ever been detected in bdelloid rotifers despite their extreme resistance to desiccation. Here we screened the genome of the bdelloid rotifer Adineta vaga for genes involved in trehalose metabolism. We discovered a total of four putative trehalose-6-phosphate synthase (TPS) and seven putative trehalase (TRE) gene copies in the genome of this ameiotic organism; however, no trehalose-6-phosphate phosphatase (TPP) gene or domain was detected. The four TPS copies of A. vaga appear more closely related to plant and fungi proteins, as well as to some protists, whereas the seven TRE copies fall in bacterial clades. Therefore, A. vaga likely acquired its trehalose biosynthesis and hydrolysis genes by horizontal gene transfers. Nearly all residues important for substrate binding in the predicted TPS domains are highly conserved, supporting the hypothesis that several copies of the genes might be functional. Besides, RNAseq library screening showed that trehalase genes were highly expressed compared to TPS genes, explaining probably why trehalose had not been detected in previous studies of bdelloids. A strong overexpression of their TPS genes was observed when bdelloids enter desiccation, suggesting a possible signaling role of trehalose-6-phosphate or trehalose in this process.
Highlights
Rotifers are microscopic invertebrates characterized by a ciliated head structure and a jaw-like grinding organ, the mastax
Identification of the Adineta vaga genes involved in trehalose metabolism
The TBLASTN search results for A. vaga homologues of trehalose phosphate synthase (TPS) from a wide range of species yielded significant E-values (< 10−10) for four predicted genes belonging to three different scaffolds in the A. vaga genomic dataset
Summary
Rotifers are microscopic invertebrates characterized by a ciliated head structure and a jaw-like grinding organ, the mastax. The degradation of trehalose, on the other hand, most commonly involves the enzyme trehalase (TRE), which catalyzes the breakdown of trehalose into two D-glucose molecules (Figure A in S1 File) [33] Disaccharides such as trehalose have never been detected in the bdelloid rotifers while most of the species appear desiccation resistant. The recently sequenced genome of A. vaga comprises the most diverse repertoire of carbohydrate-active enzymes (CAZymes) reported among metazoans so far, including 623 glycoside hydrolases (GHs, involved in the hydrolysis of sugar bonds), and 412 glycosyltransferases (GTs, responsible for building sugar bonds) [3] Inspired by this rich repertoire, the genome of A. vaga was screened here for candidate genes involved in trehalose biosynthesis and degradation and the phylogenetic origin of the TPS and TRE enzymes of bdelloid rotifers was verified. While we did not study the activity of the detected trehalose enzymes, our results start to lift the veil on the origin of the trehalose genes of A. vaga and their metabolism
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