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Two trehalase isoforms produced from a single transcript: regulation and function in drought stress tolerance in Arabidopsis thaliana

Book - Dissertation

Trehalose is a non-reducing disaccharide, consisting of two glucose molecules linked in a 1,1-glycosidic bond, and typically functions as a storage carbohydrate, structural component, and stress protectant. It is biosynthesized in a wide range of organisms such as bacteria, fungi, nematodes, arthropods, and plants. In plants trehalose is synthesized through two consecutive enzymatic reactions catalyzed by trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP). Trehalose-6-phosphate (T6P), the intermediate metabolite of trehalose biosynthesis, is considered as a central signal for sugar availability and an important regulator of the plant metabolism, growth and development. Although plants contain large families of trehalose biosynthesis-related genes, including 11 TPS genes (AtTPS1-11) and 10 TPP genes (AtTPPA-J) in the model plant Arabidopsis thaliana, only trace amounts of trehalose are present in most plants, except for some extremely drought-tolerant resurrection species (such as the spike moss Selaginella lepidophylla). In Arabidopsis, only a single gene, AtTRE1, encodes for trehalase, the enzyme catalyzing degradation of trehalose into two glucose units. So far, the regulation of trehalose breakdown has been poorly studied. In this study, we discovered the presence of two isoforms of trehalase with different subcellular localizations. They are produced from a single transcript of AtTRE1 by alternative translation initiation. The long full-length isoform (AtTRE1L) localizes at the plasma membrane while the short isoform (AtTRE1S), lacking the transmembrane domain, is localized in the cytoplasm and nucleus. These findings give more insight into how trehalase may hydrolyze both extracellular and intracellular trehalose. Next, we found that the enzyme is modified post-translationally. Consistent with its membrane localization, the AtTRE1L protein is N-glycosylated. Moreover, we also found that both trehalase isoforms are activated by phosphorylation, depending on AtCPK10, a stress-induced calcium-dependent protein kinase. Surprisingly, the two isoforms were found to interact physically and this interaction affects the nuclear localization of AtTRE1S. Finally, phenotypic analysis of the Attre1 mutant plants complemented by genomic AtTRE1L or AtTRE1S fragments revealed that both isoforms are active enzymes and that both can mediate ABA-induced stomatal closure in response to drought stress, although AtTRE1S is significantly more effective. These findings will contribute to the development of new strategies to increase plant tolerance to increasingly important drought stress conditions.
Number of pages: 17
Publication year:2020
Accessibility:Embargoed