MYB59 transcription factor behaves differently in metallicolous and non-metallicolous populations of Arabidopsis halleri

In Arabidopsis thaliana (L.) Heynh.,MYB59 transcription factor participates in regulating Ca homeostasis and signal transduction and is induced by Cd excess. To investigate its role in the facultative metallophyte Arabidopsis halleri ssp. halleri (L.) O’Kane and Al-Shehbaz, MYB59 expression was investigated under Cd treatment or Ca depletion in three populations belonging to distinct phylogeographic units (metallicolous PL22 and I16 and nonmetallicolous I29), and compared with the expression in A. thaliana. In control conditions, MYB59 transcription in A. thaliana and the non-metallicolous population I29 follow a comparable trend with higher expression in roots than shoots, whereas in metallicolous populations I16 and PL22 its expression is similar in roots and shoots, suggesting a convergent evolution associated with adaptation to metalliferous environments. After 6 h of Ca depletion, MYB59 transcript levels were very high in I16 and PL22 populations, indicating that the adaptation to metalliferous environments requires tightly regulated Ca homeostasis and signalling. Cd treatment caused variability in MYB59 expression. In I29, MYB59 expression, as in A. thaliana, is likely associated to stress response, whereas its modulation in the two metallicolous populations reflects the different strategies for Cd tolerance and accumulation. In conclusion, MYB59 regulation in A. halleri is part of the network linking mineral nutrition and Cd tolerance/accumulation

Photochemistry of oxazolidinones antibacterial drugs

The photochemistry of six N3-(3-fluoro-4-dialkylaminophenyl)-oxazolidinones known for their antimicrobial activity has been examined. All of these compounds are defluorinated in water (dec ≈ 0.25) and in methanol (dec ≈ 0.03), reasonably via the triplet. The chemical processes observed are reductive defluorination and solvolysis, depending on the structural variation introduced (thus, tethering the dialkylamino group to the aromatic ring and introducing a highly polar group in the oxazolidinone moiety have an effect). A likely mechanism involves the fragmentation of the C-F bond yielding the corresponding triplet phenyl cation. This intermediate either is reduced or, under appropriate conditions, intersystem crosses to the singlet state that adds the solvent

THE PROMOTER OF VACUOLAR METAL TRANSPORTER IN ARABIDOPSIS HALLERI: AN EXAMPLE OF EVOLUTION FOR METAL HYPERTOLERANCE/HYPERACCUMULATION

In the metal hyperaccumulator Arabidopsis halleri, the metal vacuolar transporter (VMT) isinvolved in hyperaccumulation and hypertolerance. Three VMT promoter sequences have beenidentified in the genome of A. halleri; expression analysis, conducted by GUS assay, showed thateach promoter sequence of A. halleri induced higher expression than the promoter sequence of theVMT orthologous gene in A. thaliana. Moreover, it was observed that A. halleri VTM members areexpressed in leaf trichomes, whereas VTM of A. thaliana is not present in these organs. In silicoanalysis revealed that the 5\u2019 UTR region of VTM is highly conserved between the two Arabidopsisspecies, although a dimer of MYB-binding motifs harboured by the A. halleri promoters is mutatedin a single nucleotide in the sequence of A. thaliana. Site-specific mutagenesis of these motifs in thepromoter of A. halleri indicates that they are likely involved in trichome-specific expression. Therole of these MYB-binding motifs in the A. halleri VMT promoter was tested in A. thaliana,considering their effect in both metal tolerance and accumulation. Transgenic A. thaliana plantsexpressing VMT under the control of the native A. halleri VMT promoter are more tolerant, in termsof root length, biomass production and chlorophyll content, to high metal concentrations, than theones bearing the same construct with the mutated MYB-binding motifs. Differences in shoots andin roots were also observed regarding metal accumulation. These results underline the divergentevolution of the VMT promoter, conferring higher metal tolerance, accompanied by expression intrichomes, in the hyperaccumulator A. halleri and protection to heavy metal stress in transgenic A.thaliana. Furthermore, a possible biotechnological approach might be applied in phytoremediationor biofortification programs to modulate metal content in plants

Evolution of the metal hyperaccumulation and hypertolerance traits

In this review, we overview the most updated concepts regarding the evolution of hyperaccumulation and hypertolerance, highlighting also the ecological context concerning the plant populations displaying this fascinating phenomenon

Metal detoxification in land plants: from bryophytes to vascular plants: STATE of the art and opportunities

5openInternationalItalian coauthor/editorPotentially toxic elements are a widespread concern due to their increasing diffusion into the environment. To counteract this problem, the relationship between plants and metal(loid)s has been investigated in the last 30 years. In this field, research has mainly dealt with angiosperms, whereas plant clades that are lower in the evolutive scale have been somewhat overlooked. However, recent studies have revealed the potential of bryophytes, pteridophytes and gymnosperms in environmental sciences, either as suitable indicators of habitat health and elemental pollution or as efficient tools for the reclamation of degraded soils and waters. In this review, we summarize recent research on the interaction between plants and potentially toxic elements, considering all land plant clades. The focus is on plant applicability in the identification and restoration of polluted environments, as well as on the characterization of molecular mechanisms with a potential outlet in the engineering of element tolerance and accumulation.openFasani, Elisa; Li, Mingai; Varotto, Claudio; Furini, Antonella; DalCorso, GiovanniFasani, E.; Li, M.; Varotto, C.; Furini, A.; Dalcorso, G

Metal Interactions in the Ni Hyperaccumulating Population of Noccaea caerulescens Monte Prinzera

Hyperaccumulation is a fascinating trait displayed by a few plant species able to accumulate large amounts of metal ions in above-ground tissues without symptoms of toxicity. Noccaea caerulescens is a recognized model system to study metal hyperaccumulation and hypertolerance. A N. caerulescens population naturally growing on a serpentine soil in the Italian Apennine Mountains, Monte Prinzera, was chosen for the study here reported. Plants were grown hydroponically and treated with different metals, in excess or limiting concentrations. Accumulated metals were quantified in shoots and roots by means of ICP-MS. By real-time PCR analysis, the expression of metal transporters and Fe deficiency-regulated genes was compared in the shoots and roots of treated plants. N. caerulescens Monte Prinzera confirmed its ability to hypertolerate and hyperaccumulate Ni but not Zn. Moreover, excess Ni does not induce Fe deficiency as in Ni-sensitive species and instead competes with Fe translocation rather than its uptake

Enhancement of Zn tolerance and accumulation in plants mediated by the expression of Saccharomyces cerevisiae vacuolar transporter ZRC1

Main conclusion Transgenic Arabidopsis thaliana and Populus alba plants overexpressing the zinc transporter ScZRC1 in shoots exhibit Zn tolerance. Increased Zn concentrations were observed in shoots of P. alba, a species suitable for phytoremediation. Genetic engineering of plants for phytoremediation is worth to consider if genes leading to heavy metal accumulation and tolerance are expressed in high biomass producing plants. The Saccharomyces cerevisiae ZRC1 gene encodes a zinc transporter which is primarily involved in the uptake of Zn into the vacuole. The ZRC1 gene was expressed in the model species A. thaliana and P. alba (cv. Villafranca). Both species were transformed with constructs carrying ScZRC1 under the control of either the CaMV35S promoter for constitutive expression or the active promoter region of the tobacco Rubisco small subunit (pRbcS) to limit the expression to the above-ground tissues. In hydroponic cultures, A. thaliana and poplar ScZRC1-expressing plants accumulated more Zn in vegetative tissues and were more tolerant than untransformed plants. No differences were found between plants carrying the CaMV35::ScZRC1 or pRbcS::ScZRC1 constructs. The higher Zn accumulation in transgenic plants was accompanied by an increased superoxide dismutase (SOD) activity, indicating the activation of defense mechanisms to prevent cellular damage. In the presence of cadmium in addition to Zn, plants did not show symptoms of metal toxicity, neither in hydroponic cultures nor in soil. Zn accumulation increased in shoots, while no differences were observed for Cd accumulation, in comparison to control plants. These data suggest that ectopic expression of ScZRC1 can increase the potential of poplar for the remediation of Zn-polluted soils, although further tests are required to assay its application in remediating multimetal polluted soils

Evolutionary role of a vacuolar metal transporter for hypertolerance/hyperaccumulation in Arabidopsis halleri.

VMT is a tonoplast metal transporter participating in vacuolar sequestration that is involved in metal hyperaccumulation/hypertolerance. The gene is constitutively expressed in metal hyperaccumulators, as Arabidopsis halleri, with higher transcript levels than in the corresponding non-accumulator species. In A. halleri, three different promoter sequences were identified for VMT, suggesting the presence of multiple gene copies, while a single copy is present in Arabidopsis thaliana. VMT promoter activity was compared in A. thaliana and A. halleri by GUS assay. All promoters are active in roots and guard cells, but A. halleri members drive GUS expression also in leaf mesophyll and trichomes. In silico analysis highlights, in the 5\u2019UTR of the A. halleri promoters, a dimer of MYB-binding motifs, which is mutated in a single nucleotide in the A. thaliana sequence. Promoter mutation analysis indicates that this motif is likely involved in trichome-specific expression. The high VMT transcription levels observed in trichomes of A. halleri, counteracted by its absence in A. thaliana trichomes, suggest a putative evolutionary role of VMT in the hypertolerance/hyperaccumulation trait

Diverse cis-regulation of a vacuolar metal transporter in Arabidopsis thaliana and Arabidopsis halleri.

The vacuolar metal transporter VMT is involved in metal hyperaccumulation. VMT isexpressed at higher levels in metal hyperaccumulators Arabidopsis halleri and Noccaeacaerulescens than in non-accumulator species, such as Arabidopsis thaliana. To gatherinformation about the different transcriptional cis-regulation of VMT, we performed an insilico comparison of promoter sequences amplified from a variety of Brassicaceae species,including both hyper- and non-accumulators, and three putative motifs were identified andchosen for further in vivo analysis. Three different sequences corresponding to the VMTpromoter were amplified in A. halleri. Truncated forms were generated isolating the coresequence and deleting two of the motifs, while site-directed mutagenesis was performedon the third motif. The cloned sequences were fused to the GUS reporter gene and theobtained constructs were used for A. thaliana transformation (AtVMT promoter was used ascontrol). Promoters of both A. thaliana and A. halleri VMT are active in roots, guard cellsand hydathodes, but only Ah-pVMT seems to be specific for leaf mesophyll and trichomes

Phytoremediatory efficiency of Chrysopogon zizanioides in the treatment of landfill leachate: a case study

A common approach for waste management is their disposal in landfills, which is usually associated with the production of dangerous gases and of liquid leachate. Due to its toxicity, polluted liquid negatively impacts on the environment with the possible contamination of large volumes of soil, groundwater, and surface water. Leachate remediation is therefore subject of intensive research, and phytoremediation has been achieving increasing interest in recent decades.We describe here the suitability of vetiver grass for the remediation of two leachates collected in urban landfills of northern Italy, characterized by different composition. Our objective was measuring the accumulation/tolerance potential of this species and the evapotranspiration ability in a pot experiment, to evaluate applicability of vetiver plants for the reduction and decontamination of landfill leachate. Plants were grown for 4 months in pots with a zeolite growth bed and watered with either tap water (control) or undiluted landfill leachate. Plant growth and fitness and elemental content in shoots and roots were evaluated at the end of the experiment. In these experimental conditions, the high bioaccumulation of metals highlights the suitability of this species for its employment in phytoremediation; however, vetiver growth under leachate treatment was strongly dependent on leachate composition, making a case-to-case evaluation of plant tolerance necessary before large-scale application