ABSTRACT
One of the most recent functions assigned to the TOR signaling pathway in yeast is the coordination of the transcription of genes involved in nutrient utilization. Here we show that transcription of ENA1, a gene encoding a lithium and sodium ion transporter essential for salt tolerance in yeast, is controlled by the TOR signaling pathway. First, ENA1 expression is strongly induced under TOR-inactivating conditions. Second, the absence of the TOR-controlled GATA transcription factors GLN3 and GAT1 results in reduced basal and salt-induced expression of ENA1. Third, a gln3 gat1 mutant displays a pronounced sensitivity to high concentrations of lithium and sodium. Fourth, TOR1, similar to ENA1, is required for growth under saline stress conditions. In summary, our results suggest that TOR plays a role in the general response to saline stress by regulating the transcription of ENA1 via GLN3 and GAT1.
Subject(s)
Adenosine Triphosphatases/genetics , Cation Transport Proteins , DNA-Binding Proteins/physiology , Fungal Proteins/physiology , Phosphatidylinositol 3-Kinases , Phosphotransferases (Alcohol Group Acceptor)/physiology , Repressor Proteins , Saccharomyces cerevisiae Proteins , Saccharomyces cerevisiae/drug effects , Sodium Chloride/pharmacology , Transcription Factors/physiology , Cell Cycle Proteins , RNA, Messenger/analysis , Saccharomyces cerevisiae/metabolism , Sodium-Potassium-Exchanging ATPaseABSTRACT
A target of rapamycin (TOR) protein is a protein kinase that exerts cellular signal transduction to regulate cell growth in response to extracellular nutrient conditions. In the Schizosaccharomyces pombe genome database, there are two genes encoding TOR-related proteins, but their functions have not been analyzed. Here we report that one of the genes, referred to as tor1+, is required for sexual development induced by nitrogen starvation. Ste11 is a key transcription factor for the initiation of sexual development. The expression of ste11+ is normally regulated in tor1- cells; and overexpression of ste11+ hardly rescues the defect in fertility in tor1-. Upon nitrogen starvation, tor1+ cells promote two rounds of the cell cycle to become arrested at the G1 phase before initiation of sexual development. The tor1- cells do not promote such a cell cycle, suggesting that Tor1 is necessary for the response to nitrogen starvation. The tor1- cells show no growth or very slow growth under various stress conditions, including external high pH, high concentrations of salts or sorbitol, and high temperature. These results suggest that Tor1 is necessary for any response to a wide range of stresses. The vegetative growth of tor1- cells is inhibited by rapamycin, although tor1+ cells are resistant to the drug. The tor1- cells are hypersensitive to fluphenazine and cyclosporin A, which specifically inhibit calmodulin and calcineurin, respectively.
Subject(s)
Fungal Proteins , Fungal Proteins/genetics , Phosphatidylinositol 3-Kinases , Phosphotransferases (Alcohol Group Acceptor)/genetics , Saccharomyces cerevisiae Proteins , Schizosaccharomyces pombe Proteins , Schizosaccharomyces/genetics , Schizosaccharomyces/physiology , Amino Acid Sequence , Calcium-Calmodulin-Dependent Protein Kinases/genetics , Calcium-Calmodulin-Dependent Protein Kinases/metabolism , Cell Differentiation , Cloning, Molecular , Conserved Sequence , Fungal Proteins/physiology , Gene Expression Regulation, Fungal , Genes, Fungal , Hydrogen-Ion Concentration , Molecular Sequence Data , Nitrogen/metabolism , Osmolar Concentration , Saccharomyces cerevisiae/physiology , Sequence Homology, Amino Acid , Signal Transduction/genetics , Temperature , Transcription Factors/physiologyABSTRACT
Environmental change, such as nutritional starvation, induces physiological and morphological alterations that enable fission yeast cells to survive. We isolated a novel gene, taf1+, required for the response to nitrogen starvation in the fission yeast Schizosaccharomyces pombe. taf1 disruptants could not mate upon nitrogen starvation, but could upon carbon starvation. taf1 disruptants had a defect in inducing stell+ expression under nitrogen starvation conditions. Furthermore, they lost viability quickly in nitrogen-depleted medium. Unlike wild-type cells, starved taf1-cells had nuclear chromatin that were flat and adhered to the cell periphery. These results indicate that tqf1+ is required for nitrogen starvation-induced sexual development and entering the dormant G0 state.
Subject(s)
Chromosomal Proteins, Non-Histone , Genes, Fungal , Nitrogen Fixation/physiology , Nitrogen/metabolism , Nuclear Proteins/genetics , Schizosaccharomyces pombe Proteins , Schizosaccharomyces/genetics , Amino Acid Sequence , Autophagy-Related Proteins , Fungal Proteins/genetics , Gene Deletion , Gene Expression , Molecular Sequence Data , Nitrogen Fixation/genetics , Resting Phase, Cell Cycle , Schizosaccharomyces/growth & development , Schizosaccharomyces/physiology , Transcription Factors/geneticsABSTRACT
Plant dehydroascorbate reductase (DHAR), which re-reduces oxidized ascorbate to maintain an appropriate level of ascorbate, is very important, but no gene or cDNA for plant DHAR has been cloned yet. Here, we describe a cDNA for a rice glutathione-dependent DHAR (designated DHAR1). A recombinant Dhar1p produced in Escherichia coli was functional. The expression sequence tag database suggests that Dhar1p homologs exist in various plants. Furthermore, the rice Dhar1p has a low similarity to rat DHAR, although the rice enzyme has a considerably higher specific activity than the mammalian one. The mRNA level of DHAR1, the protein level of Dhar1p and the DHAR activity in rice seedlings were elevated by high temperature, suggesting the protection role of DHAR at high temperature.
