title: Effects of phosphate deficiency and sugars on expression of rab18 in Arabidopsis: hexokinase-dependent and okadaic acid-sensitive transduction of the sugar signal.
abstract: The lack of phosphorus in the nutrient medium increased the expression of rab18, an abscisic acid (ABA)-responsive gene, in leaves of Arabidopsis thaliana. The expression of this gene was also upregulated after feeding the excised leaves with D-mannose and sucrose for both wild-type (wt) and aba1 (ABA-deficient) mutant plants. For aba1 mutants, both the phosphate deficiency and sugar effects on rab18 were weaker than in wt plants, suggesting possible involvement of both ABA-dependent and ABA-independent components in signalling. Transgenic Arabidopsis plants with increased hexokinase (HXK) expression had a much higher sucrose-dependent level of rab18 mRNA, implying the HXK involvement in sensing/transmitting the sugar signal. Sucrose-related induction of rab18 was completely inhibited by okadaic acid (OKA), suggesting the involvement of specific protein phosphatase(s) in transduction of the sugar signal. The results suggest that rab18 is regulated via interaction of a plethora of signals, including ABA, sugar and phosphate deficiency, and that the sugar effect is transmitted via a HXK-pathway, involving OKA-sensitive component(s). The findings prompt caution in linking the expression of rab18 solely to ABA signalling.
authors.affiliation: Department of Plant Physiology, Umeå Plant Science Centre, Umeå University, 901 87 Umeå, Sweden. icier@uwb.edu.pl
authors.forename: Iwona
authors.initials: I
authors.lastname: Ciereszko
authors.forename: Leszek A
authors.initials: LA
authors.lastname: Kleczkowski
mesh_terms: D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D002241:Carbohydrates / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006593:Hexokinase / Q000494:pharmacology; D008358:Mannose; D019319:Okadaic Acid / Q000494:pharmacology; D010710:Phosphates / Q000032:analysis / Q000172:deficiency*; D010937:Plant Growth Regulators; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism; D030821:Plants, Genetically Modified; D015398:Signal Transduction; D020691:rab GTP-Binding Proteins
chemical_list: D029681:Arabidopsis Proteins; D002241:Carbohydrates; D004791:Enzyme Inhibitors; D010710:Phosphates; D010937:Plant Growth Regulators; C078703:rab18 protein, Arabidopsis; D019319:Okadaic Acid; D000040:Abscisic Acid; D006593:Hexokinase; D020691:rab GTP-Binding Proteins; D008358:Mannose