Evidence for Autoregulation of Cystathionine γ-Synthase mRNA Stability in
            <i>Arabidopsis</i>

Chiba, Yasuhiro; Ishikawa, Marin; Kijima, Fumiko; Tyson, R. Huw; Kim, Jung‐Sup; Yamamoto, Ayako; Nambara, Eiji; Leustek, Thomas; Wallsgrove, R. M.; Naito, Shuichi

doi:10.1126/science.286.5443.1371

Cited by 180 publications

(245 citation statements)

References 21 publications

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“…Multiple transcripts have been found for other genes. For example, cystathione ␥-synthase mRNA in Arabidopsis was truncated at the 5Ј end in a process that was dependent on Met concentration (Chiba et al, 1999). Mutants not able to process the full-length transcript were isolated during a screen for plants that accumulate Met to high concentrations inside the cells, which highlighted the importance of such processing (Chiba et al, 1999).…”

Section: Discussionmentioning

confidence: 99%

Characterization of Arabidopsis AtAMT2, a High-Affinity Ammonium Transporter of the Plasma Membrane

et al. 2002

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AtAMT2 is an ammonium transporter that is only distantly related to the five members of the AtAMT1 family of high-affinity ammonium transporters in Arabidopsis. The short-lived radioactive ion 13 NH 4 ϩ was used to show that AtAMT2, expressed in yeast (Saccharomyces cerevisiae), is a high-affinity transporter with a K m for ammonium of about 20 m. Changes in external pH between 5.0 and 7.5 had little effect on the K m for ammonium, indicating that NH 4 ϩ , not NH 3 , is the substrate for AtAMT2. The AtAMT2 gene was expressed in all organs of Arabidopsis and was subject to nitrogen (N) regulation, at least in roots where expression was partially repressed by high concentrations of ammonium nitrate and derepressed in the absence of external N. Although expression of AtAMT2 in shoots responded little to changes in root N status, transcript levels in leaves declined under high CO 2 conditions. Transient expression of an AtAMT2-green fluorescent protein fusion protein in Arabidopsis leaf epidermal cells indicated a plasma membrane location for the AtAMT2 protein.Thus, AtAMT2 is likely to play a significant role in moving ammonium between the apoplast and symplast of cells throughout the plant. However, a dramatic reduction in the level of AtAMT2 transcript brought about by dsRNA interference with gene expression had no obvious effect on plant growth or development, under the conditions tested.Ammonium and nitrate are thought to be the primary sources of nitrogen (N) for most plants growing in agricultural soils. Acquisition of these inorganic nutrients from the soil solution involves a variety of different transporters, which transport the ions from the apoplast of root epidermal and cortical cells into the symplast. Although ammonium concentrations are often 10 to 1,000 times lower than those of nitrate in well-aerated soil, ammonium nutrition plays an essential role in waterlogged and acid soils (Marschner, 1995). Furthermore, ammonium seems to be a preferred source of N and is taken up more rapidly than nitrate when both ions are presented simultaneously to plants (Gazzarrini et al., 1999).Physiological studies of ammonium transport into roots have revealed biphasic kinetics in several species (Fried et al., 1965;Vale et al., 1988;Wang et al., 1993). The so-called high-affinity ammonium transport system is predominant at low (submillimolar) concentrations of substrate (NH 4 ϩ ) and exhibits saturation kinetics. A second component of ammonium uptake is the low-affinity transport system, which becomes significant at higher external ammonium concentrations (above 1 mm) and exhibits nonsaturation kinetics (Wang et al., 1993;Kronzucker et al., 1996). Although the molecular basis of low-affinity transport system activity remains unknown, there is growing evidence that members of the AMT1 family of transporters are responsible for high-affinity ammonium transport system activity in plants. The first AMT1 gene to be discovered in plants was AtAMT1;1 from Arabidopsis, which was cloned by complementation of a yeast (Sacchar...

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Section: Discussionmentioning

confidence: 99%

Characterization of Arabidopsis AtAMT2, a High-Affinity Ammonium Transporter of the Plasma Membrane

et al. 2002

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“…Genetic mapping and sequencing identified the causative mutation as a single base-pair change within the exon 1 coding region of the CGS gene (Chiba et al 1999). Although the exon 1 amino acid sequence is generally poorly conserved, the mto1 mutation resides within a 40-residue region that is highly conserved among plant species.…”

Section: Cgs Enzyme Is Feedback Regulated At the Level Of Mrna Stabilmentioning

confidence: 99%

“…Significant advances in our understanding on the regulation of the methionine biosynthetic pathway in plants were provided through the isolation and characterisation of genetic mutants in which methionine accumulation is altered Chiba et al 1999;Bartlem et al 2000;Goto et al 2002;Shen et al 2002;Onouchi et al 2005), as described in further detail below.…”

Section: Recycling Of Methioninementioning

confidence: 99%

Dynamics of methionine biosynthesis

Goto

Onouchi

Naito

2005

Plant Biotechnology

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“…Homoserine kinase (HSK) catalyses the formation of OPHS, which then serves as substrate for cystathionine gamma-synthase (CgS) and threonine synthase (TS). CgS and TS are regulated by SAM at the transcript (CgS in Arabidopsis; Chiba et al, 1999) or protein level (TS in Arabidopsis and potato; Curien et al, 1996Curien et al, , 1998Zeh et al, 2001), depending on the plant species (for review see Hesse and Hoefgen, 2003).…”

Section: Introductionmentioning

confidence: 99%

Regulation of aspartate-derived amino acid homeostasis in potato plants (Solanum tuberosum L.) by expression of E. coli homoserine kinase

et al. 2007

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Summary. The availability of the carbon backbone O-phosphohomoserine (OPHS) is critical to methionine (met) and threonine (thr) synthesis. OPHS derives from homoserine and is formed by homoserine kinase (HSK). To clarify the function of HSK in cellular metabolism, the E. coli HSK ortholog thrB was expressed in potato plants targeting the EcHSK protein to chloroplasts and to the cytosol. Both approaches resulted in up to 11 times increased total HSK enzyme activity. Transgenic plants exhibited reduced homoserine levels while met and thr did not accumulate significantly. However, the precursor cysteine and upstream intermediates of met such as cystathionine and homocysteine did indicating an accelerated carbon flow towards the end products. Coincidently, plants with elevated cytosolic levels of EcHSK exhibited a reduction in transcript levels of the endogenous HSK, as well as of threonine synthase (TS), cystathionine b-lyase (CbL), and met synthase (MS). In all plants, cystathionine g-synthase (CgS) expression remained relatively unchanged from wild type levels, while S-adenosylmethionine synthetase (SAMS) expression increased. Feeding studies with externally supplied homoserine fostered the synthesis of met and thr but the regulation of synthesis of both amino acids retained the wild type regulation pattern. The results indicate that excess of plastidial localised HSK activity does not influence the de novo synthesis of met and thr. However, expression of HSK in the cytosol resulted in the down-regulation of gene expression of pathway genes probably mediated via OPHS. We integrated these data in a novel working model describing the regulatory mechanism of met and thr homeostasis.

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Evidence for Autoregulation of Cystathionine γ-Synthase mRNA Stability in Arabidopsis

Cited by 180 publications

References 21 publications

Characterization of Arabidopsis AtAMT2, a High-Affinity Ammonium Transporter of the Plasma Membrane

Characterization of Arabidopsis AtAMT2, a High-Affinity Ammonium Transporter of the Plasma Membrane

Dynamics of methionine biosynthesis

Regulation of aspartate-derived amino acid homeostasis in potato plants (Solanum tuberosum L.) by expression of E. coli homoserine kinase

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