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See detailZinc triggers a complex transcriptional and post-transcriptional regulation of the metal homeostasis gene FRD3 in Arabidopsis relatives
Charlier, Jean_Benoit; Polese, Catherine; Nouet, Cécile ULg et al

in Journal of Experimental Botany (2015)

In Arabidopsis thaliana, FRD3 (Ferric Chelate Reductase Defective 3) plays a central role in metal homeostasis. FRD3 is among a set of metal homeostasis genes that are constitutively highly expressed in ... [more ▼]

In Arabidopsis thaliana, FRD3 (Ferric Chelate Reductase Defective 3) plays a central role in metal homeostasis. FRD3 is among a set of metal homeostasis genes that are constitutively highly expressed in roots and shoots of Arabidopsis halleri, a zinc hyperaccumulating and hypertolerant species. Here, we examined the regulation of FRD3 by zinc in both species to shed light on the evolutionary processes underlying the evolution of hyperaccumulation in A. halleri. We combined gene expression studies with the use of GUS and GFP reporter constructs to compare the expression profile, transcriptional and post-transcriptional regulation of FRD3 in both species. The AtFRD3 and AhFRD3 genes display a conserved expression profile. In A. thaliana, alternative transcription initiation sites from two promoters determine transcript variants which are differentially regulated by zinc supply in roots and shoots to favour the most highly translated variant under zinc excess conditions. In A. halleri, a single transcript variant with higher transcript stability and enhanced translation has been maintained. The FRD3 gene thus undergoes complex transcriptional and post-transcriptional regulation in Arabidopsis relatives. Our study reveals that a diverse set of mechanisms underlie increased gene dosage in the A. halleri lineage and illustrates how an environmental challenge can alter gene regulation. [less ▲]

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See detailFunctional analysis of the three HMA4 copies of the metal hyperaccumulator Arabidopsis halleri
Nouet, Cécile ULg; Charlier, Jean-Benoit; Carnol, Monique ULg et al

in Journal of Experimental Botany (2015), in press

In Arabidopsis halleri, the AhHMA4 gene has an essential function in Zn/Cd hypertolerance and hyperaccumulation by mediating root to shoot translocation of metals. Constitutive high expression of AhHMA4 ... [more ▼]

In Arabidopsis halleri, the AhHMA4 gene has an essential function in Zn/Cd hypertolerance and hyperaccumulation by mediating root to shoot translocation of metals. Constitutive high expression of AhHMA4 results from a tandem triplication and cis-activation of the promoter of all three copies. The three AhHMA4 copies possess divergent promoter sequences, but highly conserved coding sequences, and display identical expression profiles in the root and shoot vascular system. Here, we expressed an AhHMA4::GFP fusion under the control of each three A. halleri HMA4 promoters in a hma2hma4 double mutant of Arabidopsis thaliana to individually examine the function of each A. halleri AhHMA4 copy. The protein localized non-polarly at the plasma membrane of the root pericycle cells of both A. thaliana and A. halleri. The expression of each AhHMA4::GFP copy complemented the severe Zn deficiency phenotype of the hma2hma4 mutant by restoring root-to-shoot translocation of zinc. However, each copy had different impact on metal homeostasis in the A. thaliana genetic background: AhHMA4 copies 2 and 3 were more highly expressed and provided higher Zn tolerance in roots and accumulation in shoots than copy 1, whereas AhHMA4 copy 3 also increased Cd tolerance in roots. Our data suggest a certain extent of functional differentiation among the three A. halleri HMA4 copies, stemming from differences in expression levels rather than in expression profile. HMA4 is a key node of the Zn homeostasis network and small changes in expression level can have major impact on Zn allocation to root or shoot tissues. [less ▲]

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See detailComplex regulation of the FRD3 gene in Arabidopsis relatives
Charlier, Jean Benoit; Polese, Catherine ULg; Nouet, Cécile ULg et al

Poster (2014, March 31)

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See detailThe energetic state of mitochondria modulates complex III biogenesis through the ATP-dependent activity of Bcs1.
Ostojić, Jelena; Panozzo; Lasserre, JP et al

in Cell Metabolism (2013), 18/4

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See detailComplex regulation of the FRD3 gene in Arabidopsis relatives
Charlier, Jean-Benoit ULg; Polese, Catherine ULg; Nouet, Cécile ULg et al

Poster (2013, February 26)

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See detailPromoter analysis of three HMA4 gene copies in the zinc hyperaccumulator Arabidopsis halleri
Nouet, Cécile ULg; Cebula, Justyna; Motte, Patrick ULg et al

Poster (2012, September 20)

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See detailZinc hyperaccumulation: a model to examine metal homeostasis in plants
Hanikenne, Marc ULg; Nouet, Cécile ULg; Charlier, Jean-Benoit et al

Conference (2012, September 20)

The plant Arabidopsis halleri exhibits naturally selected metal hypertolerance and extraordinarily high levels of leaf metal accumulation. Metal hyperaccumulator species attract interest as they represent ... [more ▼]

The plant Arabidopsis halleri exhibits naturally selected metal hypertolerance and extraordinarily high levels of leaf metal accumulation. Metal hyperaccumulator species attract interest as they represent an extreme end of natural variation of the metal homeostasis network. This might be useful to reveal the global functioning of metal homeostasis networks and uncover key nodes whose alterations can drastically modify metal accumulation and tolerance. In addition, metal hyperaccumulation is a compelling model to study adaptation. In the last few years, major progress has been achieved in our understanding of the mechanisms underlying metal hyperaccumulation in A. halleri. High rates of metal uptake by roots, root-to-shoot translocation and efficient shoot vacuolar sequestration play central roles in determining hyperaccumulation and hypertolerance. Enhanced functions of several metal transporter-encoding genes result from gene copy number amplification and/or (cis)-regulatory changes. We will describe the function of several transporters in zinc and cadmium hyperaccumulation and hypertolerance, and in the adjustment of nutrient homeostasis in A. halleri. Recent work aiming to determine if selection acted during the evolutionary history of A. halleri on a loci required for metal tolerance and accumulation will be presented. [less ▲]

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See detailPromoter analysis of the three HMA4 copies in the zinc hyperaccumulator Arabidopsis halleri
Nouet, Cécile ULg; Cebula, Justyna; Motte, Patrick ULg et al

Poster (2011, August)

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See detailA Forward Genetic Screen Identifies Mutants Deficient for Mitochondrial Complex I Assembly in Chlamydomonas Reinhardtii.
Barbieri, M. R.; Larosa, Véronique ULg; Nouet, Cécile ULg et al

in Genetics (2011), 188

Mitochondrial Complex I is the largest multimeric enzyme of the respiratory chain. The lack of a model system with facile genetics has limited the molecular dissection of Complex I assembly. Using ... [more ▼]

Mitochondrial Complex I is the largest multimeric enzyme of the respiratory chain. The lack of a model system with facile genetics has limited the molecular dissection of Complex I assembly. Using Chlamydomonas reinhardtii as an experimental system to screen for Complex I defects, we isolated, via forward genetics, amc1 to 7 nuclear mutants (for assembly of mitochondrial complex I) displaying reduced or no Complex I activity. BN-PAGE and immunoblot analyses revealed that amc3 and amc4 accumulate reduced levels of the Complex I holoenzyme (950 kDa) while all other amc mutants fail to accumulate a mature complex. In amc1, 2, 5, 6, 7, the detection of a 700 kDa subcomplex retaining NADH dehydrogenase activity indicates an arrest in the assembly process. Genetic analyses established that amc5 and amc7 are alleles of the same locus while amc1 to 4 and amc6 define distinct complementation groups. The locus defined by the amc5 and amc7 alleles corresponds to the NUOB10 gene, encoding PDSW, a subunit of the membrane arm of Complex I. This is the first report of a forward genetic screen yielding the isolation of Complex I mutants. This work illustrates the potential of using Chlamydomonas as a genetically-tractable organism to decipher Complex I manufacture. [less ▲]

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See detailMetal hyperaccumulation and hypertolerance: a model for plant evolutionary genomics
Hanikenne, Marc ULg; Nouet, Cécile ULg

in Current Opinion in Plant Biology (2011), 14

In the course of evolution, plants adapted to major variations in metal availability in soils and therefore represent an important source of natural diversity of metal homeostasis networks. Thus, research ... [more ▼]

In the course of evolution, plants adapted to major variations in metal availability in soils and therefore represent an important source of natural diversity of metal homeostasis networks. Thus, research on plant metal homeostasis can provide insights into the functioning, regulation and adaptations of biological networks. Here, we describe major breakthroughs in our understanding of the genetic and molecular basis of metal hyperaccumulation and associated hypertolerance, a naturally selected complex trait which represents an extreme adaptation of the metal homeostasis network. Investigations in this field reveal further the molecular alterations underlying the evolution of natural phenotypic diversity and provide a highly relevant framework for comparative genomics. [less ▲]

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See detailChloroplastic and mitochondrial metal homeostasis.
Nouet, Cécile ULg; Motte, Patrick ULg; Hanikenne, Marc ULg

in Trends in Plant Science (2011), 16(7), 395-404

Transition metal deficiency has a strong impact on the growth and survival of an organism. Indeed, transition metals, such as iron, copper, manganese and zinc, constitute essential cofactors for many key ... [more ▼]

Transition metal deficiency has a strong impact on the growth and survival of an organism. Indeed, transition metals, such as iron, copper, manganese and zinc, constitute essential cofactors for many key cellular functions. Both photosynthesis and respiration rely on metal cofactor-mediated electron transport chains. Chloroplasts and mitochondria are, therefore, organelles with high metal ion demand and represent essential components of the metal homeostasis network in photosynthetic cells. In this review, we describe the metal requirements of chloroplasts and mitochondria, the acclimation of their functions to metal deficiency and recent advances in our understanding of their contributions to cellular metal homeostasis, the control of the cellular redox status and the synthesis of metal cofactors. [less ▲]

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See detailFunctional analysis of yeast bcs1 mutants highlights the role of Bcs1p-specific amino acids in the AAA domain.
Nouet, Cécile ULg; Truan, Gilles; Mathieu, Lise et al

in Journal of Molecular Biology (2009), 388(2), 252-61

The mitochondrial protein Bcs1p is conserved from Saccharomyces cerevisiae to humans and its C-terminal region exhibits an AAA (ATPases associated with diverse cellular activities) domain. The absence of ... [more ▼]

The mitochondrial protein Bcs1p is conserved from Saccharomyces cerevisiae to humans and its C-terminal region exhibits an AAA (ATPases associated with diverse cellular activities) domain. The absence of the yeast Bcs1p leads to an assembly defect of the iron-sulfur protein (ISP) subunit within the mitochondrial respiratory complex III, whereas human point mutations located all along the protein cause various pathologies. We have performed a structure-function analysis of the yeast Bcs1p by randomly generating a collection of respiratory-deficient point mutants. We showed that most mutations are in the C-terminal region of Bcs1p and have localized them on a theoretical three-dimensional model based on the structure of several AAA proteins. The mutations can be grouped into classes according to their respiratory competence and their location on the three-dimensional model. We have further characterized five mutants, each substituting an amino acid conserved in yeast and mammalian Bcs1 proteins but not in other AAA proteins. The effects on respiratory complex assembly and Bcs1p accumulation were analyzed. Intragenic and extragenic compensatory mutations able to restore complex III assembly to the mutants affecting the AAA domain were isolated. Our results bring new insights into the role of specific residues in critical regions that are also conserved in the human Bcs1p. We show that (1) residues located at the junction between the Bcs1p-specific and the AAA domains are important for the activity and stability of the protein and (2) the residue F342 is important for interactions with other partners or substrate proteins. [less ▲]

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See detailRmd9p controls the processing/stability of mitochondrial mRNAs and its overexpression compensates for a partial deficiency of oxa1p in Saccharomyces cerevisiae.
Nouet, Cécile ULg; Bourens, Myriam; Hlavacek, Otakar et al

in Genetics (2007), 175(3), 1105-15

Oxa1p is a key component of the general membrane insertion machinery of eukaryotic respiratory complex subunits encoded by the mitochondrial genome. In this study, we have generated a respiratory ... [more ▼]

Oxa1p is a key component of the general membrane insertion machinery of eukaryotic respiratory complex subunits encoded by the mitochondrial genome. In this study, we have generated a respiratory-deficient mutant, oxa1-E65G-F229S, that contains two substitutions in the predicted intermembrane space domain of Oxa1p. The respiratory deficiency due to this mutation is compensated for by overexpressing RMD9. We show that Rmd9p is an extrinsic membrane protein facing the matrix side of the mitochondrial inner membrane. Its deletion leads to a pleiotropic effect on respiratory complex biogenesis. The steady-state level of all the mitochondrial mRNAs encoding respiratory complex subunits is strongly reduced in the Deltarmd9 mutant, and there is a slight decrease in the accumulation of two RNAs encoding components of the small subunit of the mitochondrial ribosome. Overexpressing RMD9 leads to an increase in the steady-state level of mitochondrial RNAs, and we discuss how this increase could suppress the oxa1 mutations and compensate for the membrane insertion defect of the subunits encoded by these mRNAs. [less ▲]

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