Title: The role of the Arabidopsis trehalase and the trehalose-6-phosphate phosphatases during drought stress, growth and development
Other Titles: De rol van trehalase en trehalose-6-fosfaat fosfatasen in Arabidopsis tijdens droogte stress, plantengroei en -ontwikkeling
Authors: Van Houtte, Hilde
Issue Date: 23-May-2013
Abstract: Trehalose is a nonreducing disaccharide linking two glucose units in an alpha,alpha-1,1 configuration. It is a common sugar in bacteria, fungi and yeast, where it functions as a carbon source and stress protectant. The major trehalose biosynthesis pathway involves two consecutive enzymatic reactions mediated by trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP). The intermediate compound trehalose-6-phosphate (T6P) has recently emerged as a growth regulator and a coordinator of the plant metabolism. Plants contain only small amounts of trehalose but encode large families of trehalose biosynthesis genes. Out of the 11 TPS proteins of Arabidopsis thaliana, only AtTPS1 was found to display TPS activity. In contrast, all 10 TPP proteins of Arabidopsis (AtTPPA-J) are active TPP enzymes. Arabidopsis contains also one trehalase enzyme, AtTRE1, which hydrolyzes trehalose into glucose.In this work, we analyzed the Arabidopsis TPPs and trehalase to gain more insight in the role of the trehalose metabolism during plant growth, development and drought stress. AtTPPA-J gene expression assays in Arabidopsis suggest that the regulation of the TPPs is highly specific in response to altered sugar availability and light conditions. Arabidopsis TPPs, possible regulators of T6P levels, seem to control specific processes in plant development. AtTPPB expression levels are negatively correlated with leaf size and cell division, while AtTPPA and AtTPPG execute redundant roles during the differentiation of trichoblast and atrichoblast cells in the root.Ectopic expression of trehalose biosynthesis genes in plants has been used in the past to increase trehalose synthesis, thereby hoping to generate stress tolerant plants. The abiotic stress tolerance of the plants improved but the trehalose levels remained low. Trehalase, the only known plant enzyme able to degrade trehalose, might be responsible for these suppressed trehalose levels. Arabidopsis plants modified in AtTRE1 expression were generated to test this assumption and were subjected to drought stress. AtTRE1-overexpressing plants contain reduced trehalose levels but recover better after drought stress, whereas Attre1 mutants display increased trehalose contents and a drought-susceptible phenotype. Water-retaining capacities of the AtTRE1-modified plants were consistent with the drought stress phenotypes. In addition, ABA-mediated stomatal closure is impaired in Attre1 mutants, while AtTRE1 overexpressors are hypersensitive towards ABA in their guard cells. Consistent with this finding are the altered leaf temperatures of AtTRE1-modified plantlets during in vivo drought stress experiments. All these data support that overexpression of AtTRE1 enhances drought stress tolerance in Arabidopsis and suggest an important role for trehalase in the control of stomatal regulation in the drought stress response.A link between AtTRE1 and lateral root development was found in the Attre1-3OE mutant. This T-DNA insertion mutant contains a CaMV 35S element in the 3’ end of the AtTRE1 promoter, resulting in the overexpression of AtTRE1 and the disruption of two cis-acting elements. It is hypothesized that the design of the AtTRE1 promoter in the Attre1-3OE mutant is responsible for a deregulated overexpression of AtTRE1 upon auxin signaling, leading to a twisted root phenotype and the tendency for early lateral root formation. AtTRE1 expression is observed in the root tip, central stele and oscillation zone, where many auxin-induced responses occur. Feeding sugars aggravates the early lateral root phenotype and causes root growth arrest in the Attre1-3OE seedlings. These results indicate that AtTRE1 is involved in the control of root growth and lateral root initiation, possibly through the modulation of auxin and sugar signals.AtTRE1-modified plants display phenotypes associated with impaired T6P signaling. AtTRE1 overexpression is related with a decreased leaf area and leaf epidermal cell number. AtTRE1 overexpressors show the tendency to accumulate less UDP-glucose and sugar phosphates, while the opposite trend is seen in Attre1 mutants. It was found that high AtTRE1 transcripts promote SnRK1 signaling in seedlings. In addition, AtTRE1 influences the transition to flowering, since early and late flowering phenotypes are observed in AtTRE1-modified plants. AtTRE1 expression patterns suggest a role for AtTRE1 in phloem loading/unloading processes and seed development. These data indicate that AtTRE1 is involved in T6P and SnRK1 signaling during growth and development in Arabidopsis plants.
Table of Contents: TABLE OF CONTENTS p. i
CHAPTER 1: Literature overview p.1
CHAPTER 2: Redundant and non-redundant roles of the Arabidopsis TPPs p. 41
CHAPTER 3: Overexpression of AtTRE1 leads to increased drought stress tolerance p. 49
CHAPTER 4: AtTRE1 and its role in lateral root development p. 69
CHAPTER 5: A tight regulation of AtTRE1 expression is required for effective T6P p. 87
CHAPTER 6: General conclusion and perspectives p. 121
APPENDIX: Arabidopsis thaliana wild-type and trehalase-modified lines p. 135
ISBN: 978-90-8649-615-0
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Molecular Microbiology and Biotechnology Section - miscellaneous

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