Arginase Is Inoperative in Developing Soybean Embryos1

Goldraij, Ariel; Polacco, Joseph C.

doi:10.1104/pp.119.1.297

Cited by 67 publications

(59 citation statements)

References 32 publications

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“…For example, in soybean, arginase activity is low during embryo development when Arg is deposited, rising steeply during germination when Arg is turned over. This separates the reactions of the urea cycle in time (Goldraij and Polacco, 1999). Plant arginases possess particularly high K m constants (greater than 50 mM), Figure 6.…”

Section: Discussionmentioning

confidence: 99%

Identification and Characterization of Proteins Involved in Rice Urea and Arginine Catabolism

Cao

Werner²,

Dahncke³

et al. 2010

Plant Physiology

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Rice (Oryza sativa) production relies strongly on nitrogen (N) fertilization with urea, but the proteins involved in rice urea metabolism have not yet been characterized. Coding sequences for rice arginase, urease, and the urease accessory proteins D (UreD), F (UreF), and G (UreG) involved in urease activation were identified and cloned. The functionality of urease and the urease accessory proteins was demonstrated by complementing corresponding Arabidopsis (Arabidopsis thaliana) mutants and by multiple transient coexpression of the rice proteins in Nicotiana benthamiana. Secondary structure models of rice (plant) UreD and UreF proteins revealed a possible functional conservation to bacterial orthologs, especially for UreF. Using aminoterminally StrepII-tagged urease accessory proteins, an interaction between rice UreD and urease could be shown. Prokaryotic and eukaryotic urease activation complexes seem conserved despite limited protein sequence conservation for UreF and UreD. In plant metabolism, urea is generated by the arginase reaction. Rice arginase was transiently expressed as a carboxylterminally StrepII-tagged fusion protein in N. benthamiana, purified, and biochemically characterized (K m = 67 mM, k cat = 490 s 21 ). The activity depended on the presence of manganese (K d = 1.3 mM). In physiological experiments, urease and arginase activities were not influenced by the external N source, but sole urea nutrition imbalanced the plant amino acid profile, leading to the accumulation of asparagine and glutamine in the roots. Our data indicate that reduced plant performance with urea as N source is not a direct result of insufficient urea metabolism but may in part be caused by an imbalance of N distribution.

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Section: Discussionmentioning

confidence: 99%

Identification and Characterization of Proteins Involved in Rice Urea and Arginine Catabolism

Cao

Werner²,

Dahncke³

et al. 2010

Plant Physiology

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“…Seed and leaf (10th trifoliate) tissue extraction and urea determination were performed as described by Goldraij and Polacco (1999) and Stebbins et al (1991), respectively.…”

Section: Urea Content and Urease Activity Analysesmentioning

confidence: 99%

“…In soybean (Glycine max [L.] Merrill), this is particularly important during germination when storage proteins are mobilized to nourish the seedling. Most of the large endogenously generated urea pool comes from Arg (Stebbins and Polacco, 1995), which constitutes 18% of storage protein N (Micallef and Shelp, 1989) and is actively degraded to urea and Orn upon germination (Goldraij and Polacco, 1999). Urease catalyzes N reconversion from urea to ammonia, which is subsequently assimilated via Gln synthetase (Lam et al, 1996).…”

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Interallelic Complementation at the Ubiquitous Urease Coding Locus of Soybean

2003

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Soybean (Glycine max [L.] Merrill) mutant aj6 carries a single recessive lesion, aj6, that eliminates ubiquitous urease activity in leaves and callus while retaining normal embryo-specific urease activity. Consistently, aj6/aj6 plants accumulated urea in leaves. In crosses of aj6/aj6 by urease mutants at the Eu1, Eu2, and Eu3 loci, F 1 individuals exhibited wild-type leaf urease activity, and the F 2 segregated urease-negative individuals, demonstrating that aj6 is not an allele at these loci. F 2 of aj6/aj6 crossed with a null mutant lacking the Eu1-encoded embryo-specific urease showed that ubiquitous urease was also inactive in seeds of aj6/aj6. The cross of aj6/aj6 to eu4/eu4, a mutant previously assigned to the ubiquitous urease structural gene (R.S. Torisky, J.D. Griffin, R.L. Yenofsky, J.C. Polacco [1994] Mol Gen Genet 242: 404-414), yielded an F 1 having 22% Ϯ 11% of wild-type leaf urease activity. Coding sequences for ubiquitous urease were cloned by reverse transcriptase-polymerase chain reaction from wild-type, aj6/aj6, and eu4/eu4 leaf RNA. The ubiquitous urease had an 837-amino acid open reading frame (ORF), 87% identical to the embryo-specific urease. The aj6/aj6 ORF showed an R201C change that cosegregated with the lack of leaf urease activity in a cross against a urease-positive line, whereas the eu4/eu4 ORF showed a G468E change. Heteroallelic interaction in F 2 progeny of aj6/aj6 ϫ eu4/eu4 resulted in partially restored leaf urease activity. These results confirm that aj6/aj6 and eu4/eu4 are mutants affected in the ubiquitous urease structural gene. They also indicate that radical amino acid changes in distinct domains can be partially compensated in the urease heterotrimer.The main function of urease in plants is to recycle N from urea. In soybean (Glycine max [L.] Merrill), this is particularly important during germination when storage proteins are mobilized to nourish the seedling. Most of the large endogenously generated urea pool comes from Arg (Stebbins and Polacco, 1995), which constitutes 18% of storage protein N (Micallef and Shelp, 1989) and is actively degraded to urea and Orn upon germination (Goldraij and Polacco, 1999). Urease catalyzes N reconversion from urea to ammonia, which is subsequently assimilated via Gln synthetase (Lam et al., 1996). Urease also recycles N derived from urea exogenously applied as a foliar fertilizer (Witte et al., 2002). A potential urease role in maintaining N 2 fixation under water stress was posited in a model by Purcell et al. (2000) and Vadez and Sinclair (2001), whereby urea is generated directly from ureides in soybean cultivars (e.g. Maple arrow) able to fix N 2 under water deficit. Ureides are converted to urea in reactions that are not affected by water deficit thus avoiding ureide buildup and its inhibition of N fixation (Serraj et al., 1999). In this model, urease is essential to N use in soybean cultivars adapted to dry areas where fixed N is the sole or major N source. Drought-sensitive cultivars, however, are purported to bypass urea p...

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“…In plants, urea originates from the breakdown of Arg, especially important during germination (Zonia et al, 1995;Goldraij and Polacco, 1999), and from purines or ureides. Because ureides serve as nitrogen-transport compounds in nitrogenfixing legumes their degradation has received special attention Todd and Polacco, 2004).…”

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Identification of Three Urease Accessory Proteins That Are Required for Urease Activation in Arabidopsis

2005

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Urease is a nickel-containing urea hydrolase involved in nitrogen recycling from ureide, purine, and arginine catabolism in plants. The process of urease activation by incorporation of nickel into the active site is a prime example of chaperonemediated metal transfer to an enzyme. Four urease accessory proteins are required for activation in Klebsiella aerogenes. In plants urease accessory proteins have so far been only partially defined. Using reverse genetic tools we identified four genes that are necessary for urease activity in Arabidopsis (Arabidopsis thaliana; ecotypes Columbia and Nö ssen). Plants bearing T-DNA or Ds element insertions in either the structural gene for urease or in any of the three putative urease accessory genes AtureD, AtureF, and AtureG lacked the corresponding mRNAs and were defective in urease activity. In contrast to wild-type plants, the mutant lines were not able to support growth with urea as the sole nitrogen source. To investigate whether the identified accessory proteins would be sufficient to support eukaryotic urease activation, the corresponding cDNAs were introduced into urease-negative Escherichia coli. In these bacteria, urease activity was observed only when all three plant accessory genes were coexpressed together with the plant urease gene. Remarkably, plant urease activation occurred as well in cell-free E. coli extracts, but only in extracts from cells that had expressed all three accessory proteins. The future molecular dissection of the plant urease activation process may therefore be performed in vitro, providing a powerful tool to further our understanding of the biochemistry of chaperone-mediated metal transfer processes in plants.

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Arginase Is Inoperative in Developing Soybean Embryos1

Cited by 67 publications

References 32 publications

Identification and Characterization of Proteins Involved in Rice Urea and Arginine Catabolism

Identification and Characterization of Proteins Involved in Rice Urea and Arginine Catabolism

Interallelic Complementation at the Ubiquitous Urease Coding Locus of Soybean

Identification of Three Urease Accessory Proteins That Are Required for Urease Activation in Arabidopsis

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