Minisymposium 15: In Response to Water

Abs # 27001: AtTPS1, the Arabidopsis trehalose-6-P-synthase gene, regulates glucose sensing and ABA signaling genes

Presenter:	Iturriaga, Gabriel , iturri@cib.uaem.mx
Authors	Iturriaga, Gabriel  (A)   Avonce, Nelson  (A)   Mascorro-Gallardo, Oscar  (C)   Van Dijck, Patrick  (B)   Thevelein, Johan M. (B)
Affiliations:	(A): Centro de Investigacion en Biotecnologia, Universidad Autonoma del Estado de Morelos (B): Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven (C): Departamento de Fitotecnia, Universidad Autonoma Chapingo

Trehalose is a nonreducing disaccharide which accumulates in a wide variety of organisms that withstand drought, salt, heat or freezing stress. Trehalose biosynthesis involves conversion of UDP-glucose and glucose-6-phosphate to trehalose-6-phosphate by trehalose-6-phosphate synthase (TPS1) and dephosphorylation to trehalose by trehalose-6-phosphate phosphatase (TPP). In higher plants, trehalose rarely occurs, excluding its role as an osmoprotectant, although an Arabidopsis thaliana AtTPS1 homologue is able to synthesize trehalose after complementation in yeast. Also, using the trehalase inhibitor validamycin A, trehalose accumulates in plants at low levels. In fact, in the past few years it has been found that most plants including non-stress tolerant species encode TPS1 transcripts, after analysis of many ESTs collections. Thus, besides of its role in trehalose synthesis, TPS1 has other possible roles in plants. Recently, it has been reported that an Arabidopsis transposable-insertion mutant in AtTPS1 gene was affected in embryo maturation and growth. Here we report that overexpression of AtTPS1 in Arabidopsis using the 35S promoter leads to a low trehalose accumulation. Nevertheless, transgenic plants displayed dehydration tolerance, glucose- and ABA-insensitive phenotypes in seedlings and delayed flowering in adult plants. Transgenic seedlings germinated on glucose are visibly larger with green well-expanded cotyledonary leaves and fully developed roots, in contrast to wild type seedlings which show growth retardation, short unexpanded leaves without chlorophyll and absence of root elongation. When transgenic seeds were germinated without prior cold treatment, their germination rate was higher compared to wild type seedlings, suggesting an arrested dormancy. Germination in the presence of different concentrations of ABA revealed higher germination rate for transgenic plants overexpressing AtTPS1, although ABA concentration remain unchanged compared to wild type plants. Expression analysis of several genes in transgenic plants showed up-regulation of ABI5, HXKI, HXKII, RBSC and APL3 genes, whereas in the presence of glucose ABI4 was down-regulated. Analysis of AtTPS1 in HXK-antisense or HXK-sense transgenic lines, revealed its involvement in HXK-dependent glucose signaling pathway. These data strongly suggest that AtTPS1 has a pivotal role in the regulation of glucose sensing and ABA signaling genes during vegetative development.