An Arabidopsis GSK3/shaggy-Like Gene That Complements Yeast Salt Stress-Sensitive Mutants Is Induced by NaCl and Abscisic Acid

Abstract

GSK3/shaggy-like genes encode kinases that are involved in a variety of biological processes. By functional complementation of the yeast calcineurin mutant strain DHT22-1a with a NaCl stresssensitive phenotype, we isolated the Arabidopsis cDNA AtGSK1, which encodes a GSK3/shaggy-like protein kinase. AtGSK1 rescued the yeast calcineurin mutant cells from the effects of high NaCl. Also, the AtGSK1 gene turned on the transcription of the NaCl stress-inducible PMR2A gene in the calcineurin mutant cells under NaCl stress. To further define the role of AtGSK1 in the yeast cells we introduced a deletion mutation at the MCK1 gene, a yeast homolog of GSK3, and examined the phenotype of the mutant. The mck1 mutant exhibited a NaCl stress-sensitive phenotype that was rescued by AtGSK1. Also, constitutive expression of MCK1 complemented the NaCl-sensitive phenotype of the calcineurin mutants. Therefore, these results suggest that Mck1p is involved in the NaCl stress signaling in yeast and that AtGSK1 may functionally replace Mck1p in the NaCl stress response in the calcineurin mutant. To investigate the biological function of AtGSK1 in Arabidopsis we examined the expression of AtGSK1. Northern-blot analysis revealed that the expression is differentially regulated in various tissues with a high level expression in flower tissues. In addition, the AtGSK1 expression was induced by NaCl and exogenously applied ABA but not by KCl. Taken together, these results suggest that AtGSK1 is involved in the osmotic stress response in Arabidopsis.

Abscisic Acid Biosynthesis and Response

“…ABA may enhance either expression (Hwang and Goodman, 1995;Hong et al, 1997;Lee et al, 1998;Mikami et al, 1998;GomezCadenas et al, 1999;Piao et al, 1999) or activity (Li and Assmann, 1996;Burnett et al, 2000) of these kinases. Although initial functional studies with pharmacological inhibitors did not discriminate among the roles of individual family members, recent studies with dominant negative alleles have assayed the role of specific kinases (Sheen, 1996;Li et al, 2000).…”

“…The use of ABA analogs in germination and gene expression bioassays has allowed the inference of multiple ABA receptors with different structural requirements for activity in different response pathways (Walker-Simmons et al, 1997;Kim et al, 1999). Given the lack of concrete leads, the search for ABA receptors should include intracellular compartments, proteins regulated by or involved in ABA responses, and non-proteinaceous molecules.…”

Abscisic Acid Uridine Diphosphate Glucosyltransferases Play a Crucial Role in Abscisic Acid Homeostasis in Arabidopsis

“…For NaCl, ABA, or mannitol treatment, plants grown in 1/2 MS liquid medium for 10 d were treated with 100 mM NaCl, 100 mM ABA, or 300 mM mannitol, respectively, for the indicated times as described previously (Piao et al, 1999).…”

Direct and Novel Regulation of cAMP-dependent Protein Kinase by Mck1p, a Yeast Glycogen Synthase Kinase-3

“…More recently, MCK1 and RIM11 have been implicated in the protein ubiquitination pathway (16). Finally, MCK1 has been implicated in the response to high concentrations of NaCl in growth medium (17).…”