Isolation and Characterization of an Arabidopsis Mutant That Overaccumulates O-Acetyl-l-Ser

Abstract

O-Acetyl-L-Ser (OAS) is a positive regulator for the expression of sulfur (S) deficiency-inducible genes. In this study, through the isolation and analysis of Arabidopsis mutants exhibiting altered expression of S-responsive genes, we identified a thiol reductase as a regulator of the OAS levels. Ethyl methanesulfonate-mutagenized M2 seeds of transgenic Arabidopsis NOB7 carrying a chimeric S-responsive promoter driving the green fluorescent protein gene were screened for mutants with altered levels of green fluorescence compared to parental NOB7 line. One of the lines exhibited elevated levels of green fluorescence and mRNA accumulation of several endogenous S-responsive genes and carried a single recessive mutation responsible for the phenotype. OAS concentration in the rosette leaves of the mutant was about five times higher than that of wild-type plants. Based upon the high OAS levels, the mutant was named osh1-1 (OAS high accumulation). The OSH1 locus was mapped to a 30-kb region in chromosome V. DNA sequence analysis revealed no base change in this region; however, a demethylated C residue was found in the first exon of At5g01580. At5g01580 mRNA accumulation was higher in osh1-1 than in wild type, while transcript levels of other genes in the mapped region were not significantly altered in osh1-1. A line of transgenic plants overexpressing At5g01580 had elevated levels of endogenous S-responsive genes. These results suggest that elevated expression of At5g01580 is the cause of osh1 phenotype. Based on sequence similarity to animal thiol reductases, At5g01580 was tested for and exhibited thiol reductase activity. Possible roles of a thiol reductase in OAS metabolism are discussed.

A Genome-Wide and Metabolic Analysis Determined the Adaptive Response of Arabidopsis Cells to Folate Depletion Induced by Methotrexate

“…We suggest that the increase in Ser levels in MTX-treated cells was at the origin of the elevation of OAS through an increased activity of Ser acetyltransferase. This assumption is supported by the previous finding that Ser application to Arabidopsis plants increased OAS levels and induced S deficiency response (Ohkama-Ohtsu et al, 2004). Also, in cells treated with MTX and LV, we found that the accumulation of Ser, OAS, and transcripts of the S-responsive gene APR1 was less important and delayed as compared to cells treated with MTX alone (Fig.…”

Arabidopsis thaliana26S Proteasome Subunits RPT2a and RPT5a Are Crucial for Zinc Deficiency-Tolerance

“…Semi-quantitative RT-PCR was conducted with optimum cycles for each gene. The primer sets for the analyzes genes were as follows: a set for RPT2a was same as described by Sonoda et al; 9) 5 0 -AAGTCAGCGGAGACAGGGAA-3 0 (F) and 5 0 -TAGATGATCCTGATTCGAAAAC-3 0 (R) for RPT5a; a set for Actin8 was same as described by Ohtsu et al 20) Actin8 transcript was used as a reference. Quantitative real-time RT-PCR was performed with SYBER premix exTaq Ò II (Takara) on a Thermal Cycler Dice Ò Real Time System (Takara).…”

Inactivation of Thioredoxin Reductases Reveals a Complex Interplay between Thioredoxin and Glutathione Pathways in Arabidopsis Development

“…Such proteins should present special characteristics: the redox center of the Arabidopsis NTRs is situated in a groove and is only accessible to proteins with a disulfide bridge on the surface of a small molecule or on an appendage of a large molecule (Dai et al, 1996). To date, such structures have been described only for the thioredoxin superfamily and, more recently, for the g-interferon-inducible thiol reductases (Hastings et al, 2006), with six homologs in the Arabidopsis genome, one of them implicated in high O-acetyl-LSer accumulation (Ohkama-Ohtsu et al, 2004).…”