Project description:The transition metal copper (Cu) is an essential element for all living organisms. In plants, Cu plays key roles in electron transport chains of chloroplasts and mitochondria, as well as in cell wall metabolism, ethylene perception, molybdenum cofactor synthesis and oxidative stress protection. Because of its physiological importance, suboptimal concentrations of Cu trigger a re-organization of metabolism to economize on Cu, and pronounced Cu deficiency causes severe growth reduction and defects in male fertility. However, when present in excess, Cu can be highly toxic. Therefore, Cu uptake, utilization and cellular concentrations are strictly regulated. A number of components of the Cu-homeostatic network of Arabidopsis have already been identified. However, the mechanisms that control responses of plant gene expression to Cu-deficiency are only partly understood. In Chlamydomonas reinhardtii, the transcription factor Crr1 is required for activating and/or repressing the expression of a number of genes in response to Cu deficiency. This protein contains a plant-specific DNA-binding domain (SBP domain), ankyrin repeats and a C-terminal cysteine-rich region with similarity to a Drosophila metallothionein (MT). In Arabidopsis, there is a family of 16 proteins with SBP domains named SPL family (SBP-like) of which a subset of proteins have been implicated in flowering time control and floral development. Among all of them, AtSPL7 is the most similar to Crr1 (27 % identity), and AtSPL1 (25 % identity), AtSPL12 (24 % identity) and AtSPL14 (23 % identity) share a common protein architecture. The goal of this work was to obtain a complete account of the response of the Arabidopsis thaliana transcriptome to Cu deficiency, as well as to determine the role of AtSPL7 in the transcriptional response to Cu deficiency. For this purpose, three independent experiments were carried out including Col-0 wild-type and spl7-2 mutant plants grown in Cu-sufficient and Cu-deficient hydroponic media, respectively. Root and shoot transcriptomes were established by RNA-Seq for quantitative comparisons. Sampling of root and shoot tissues of wild-type (WT, Col-0) and spl7-2 mutant plants (the mutant is knock-down for the transcription factor SPL7, which plays a key role in the transcriptional regulation of the copper deficiency responses) cultivated hydroponically in a modified Hoagland's solution under Cu-sufficient (control) and Cu-deficient conditions.

Project description:The transition metal copper (Cu) is an essential element for all living organisms. In plants, Cu plays key roles in electron transport chains of chloroplasts and mitochondria, as well as in cell wall metabolism, ethylene perception, molybdenum cofactor synthesis and oxidative stress protection. Because of its physiological importance, suboptimal concentrations of Cu trigger a re-organization of metabolism to economize on Cu, and pronounced Cu deficiency causes severe growth reduction and defects in male fertility. However, when present in excess, Cu can be highly toxic. Therefore, Cu uptake, utilization and cellular concentrations are strictly regulated. A number of components of the Cu-homeostatic network of Arabidopsis have already been identified. However, the mechanisms that control responses of plant gene expression to Cu-deficiency are only partly understood. In Chlamydomonas reinhardtii, the transcription factor Crr1 is required for activating and/or repressing the expression of a number of genes in response to Cu deficiency. This protein contains a plant-specific DNA-binding domain (SBP domain), ankyrin repeats and a C-terminal cysteine-rich region with similarity to a Drosophila metallothionein (MT). In Arabidopsis, there is a family of 16 proteins with SBP domains named SPL family (SBP-like) of which a subset of proteins have been implicated in flowering time control and floral development. Among all of them, AtSPL7 is the most similar to Crr1 (27 % identity), and AtSPL1 (25 % identity), AtSPL12 (24 % identity) and AtSPL14 (23 % identity) share a common protein architecture. The goal of this work was to obtain a complete account of the response of the Arabidopsis thaliana transcriptome to Cu deficiency, as well as to determine the role of AtSPL7 in the transcriptional response to Cu deficiency. For this purpose, three independent experiments were carried out including Col-0 wild-type and spl7-2 mutant plants grown in Cu-sufficient and Cu-deficient hydroponic media, respectively. Root and shoot transcriptomes were established by RNA-Seq for quantitative comparisons.

Project description:Metallothioneins are ubiquitous, small, cysteine-rich proteins with the ability to bind heavy metals. In spite of their biochemical characterization, their in vivo function remains elusive. Here, we report the generation of a metallothionein gene family knockout in Drosophila melanogaster by targeted disruption of all four genes (MtnA to -D). These flies are viable if raised in standard laboratory food. During development, however, they are highly sensitive to copper, cadmium, and (to a lesser extent) zinc load. Metallothionein expression is particularly important for male viability; while copper load during development affects males and females equally, adult males lacking metallothioneins display a severely reduced life span, possibly due to copper-mediated oxidative stress. Using various reporter gene constructs, we find that different metallothioneins are expressed with virtually the same tissue specificity in larvae, notably in the intestinal tract at sites of metal accumulation, including the midgut's "copper cells." The same expression pattern is observed with a synthetic minipromoter consisting only of four tandem metal response elements. From these and other experiments, we conclude that tissue specificity of metallothionein expression is a consequence, rather than a cause, of metal distribution in the organism. The bright orange luminescence of copper accumulated in copper cells of the midgut is severely reduced in the metallothionein gene family knockout, as well as in mutants of metal-responsive transcription factor 1 (MTF-1), the main regulator of metallothionein expression. This indicates that an in vivo metallothionein-copper complex forms the basis of this luminescence. Strikingly, metallothionein mutants show an increased, MTF-1-dependent induction of metallothionein promoters in response to copper, cadmium, silver, zinc, and mercury. We conclude that free metal, but not metallothionein-bound metal, triggers the activation of MTF-1 and that metallothioneins regulate their own expression by a negative feedback loop.

Dataset Information

Syntaxin 5 is required for copper homeostasis in Drosophila and mammals.

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Syntaxin 5 is required for copper homeostasis in Drosophila and mammals.

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