Nickel resistance and chromatin condensation in Saccharomyces cerevisiae expressing a maize high mobility group I/Y protein

Epigenetic modifications preserve the hyperaccumulator Noccaea caerulescens from Ni geno-toxicity

The Ni hyperaccumulator Noccaea caerulescens has adapted to live in a naturally stressed environment, evolving a complex pattern of traits to cope with adverse conditions. Evidence is accumulating regarding the important role of epigenetic modifications in regulating plant responses to stress. In this study, we present data from the natural "open-field" adaptation of the Ni hyperaccumulator N. caerulescens to serpentine soil and provide the first evidence of the involvement of epigenetic changes in response to the high Ni content present in plant leaves. The alkaline comet assay revealed the integrity of the nuclei of leaf cells of N. caerulescens grown in a Ni-rich environment, while in the non-tolerant Arabidopsis thaliana exposed to Ni, the nuclei were severely damaged. DNA of N. caerulescens plants grown in situ were considerably hyper-methylated compared to A. thaliana plants exposed to Ni. In addition, qRT-PCR revealed that N. caerulescens MET1, DRM2, and HDA8 genes involved in epigenetic DNA and histone modification were up-regulated in the presence of high Ni content in leaves. Such epigenetic modifications may constitute a defense strategy that prevents genome instability and direct damage to the DNA structure by Ni ion, enabling plants to survive in an extreme environment. Further studies will be necessary to analyze in detail the involvement of DNA methylation and other epigenetic mechanisms in the complex process of metal hyperaccumulation and plants' adaptive response. Environ. Mol. Mutagen. 59:464-475, 2018. © 2018 Wiley Periodicals, Inc.

Characterization of a cDNA from Beta maritima that confers nickel tolerance in yeast

Nickel is an essential micronutrient due to its involvement in many enzymatic reactions as a cofactor. However, excess of this element is toxic to biological systems. Here, we constructed a cDNA library from Beta maritima and screened it in the yeast system to identify genes that confer resistance to toxic levels of nickel. A cDNA clone (NIC6), which encodes for a putative membrane protein with unknown function, was found to help yeast cells to tolerate toxic levels of nickel. A GFP fused form of Nic6 protein was localized to multivesicular structures in tobacco epidermal cells. Thus, our results suggest a possible role of Nic6 in nickel and intracellular ion homeostasis.

Both trivalent and hexavalent chromium strongly alter in vitro germination and ultrastructure of kiwifruit pollen

Due to its widespread industrial use, chromium is considered a dangerous environmental pollutant. It is known to inhibit plant growth and development. The present study provides the first evidence of the toxicity of this metal on the male haploid generation of a higher plant. Both Cr(III) and Cr(VI) species, supplied as CrCl(3) and CrO(3), respectively, exerted a strong dose-dependent inhibitory effect on kiwifruit pollen tube emergence and growth. Cr(III) resulted more effective than Cr(VI) in the 16-75microM interval; moreover, complete inhibition of germination was attained at much lower doses than Cr(VI). Also tube morphology was affected. While the plasma membrane was still undamaged in the large majority of the treated pollen grains, dramatic ultrastructural alterations were induced by chromium including chromatin condensation, swelling of mitochondria, cytoplasmic vacuolization, and perturbed arrangement of endoplasmic reticulum cisternae. Thus, it seems that the impact of the two chromium species on kiwifruit pollen may result in severe compromission of both essential structures and functions of the male gametophyte.

Analysis of pea HMG-I/Y expression suggests a role in defence gene regulation

SUMMARY HMG-I/Y proteins are characterized by the presence of AT-hook motifs, DNA binding domains that recognize AT-rich tracts of DNA. By facilitating protein:protein and protein:DNA interactions in the vicinity of these AT-rich binding sites, HMG-I/Y positively or negatively regulates gene expression. Several pea defence gene promoters have AT-rich tracts of DNA that are potential targets for modulation via HMG-I/Y. In this study, a comparison of the expression of a pea defence gene (DRR206) mRNA relative to the expression of HMG-I/Y mRNA was monitored by Northern analysis following the inoculation of a fungal pathogen, Fusarium solani or treatment with chitosan and a F. solani DNase (Fsph DNase). In pea pod endocarp tissue, HMG-I/Y expression was observed at high levels in untreated tissue and at lower levels 6 h following inoculation or wounding of the tissue. Western blots with an antipea HMG-I/Y polyclonal antibody also revealed that pea HMG-I/Y is expressed at decreased levels 6 h following inoculation or elicitor treatment. HMG-I/Y extracted from pea caused alterations in the gel migration of radio-labelled AT-rich sequences from the pea DRR206 promoter, suggesting that similar interactions could exist in vivo. Agroinfiltration was utilized to express the pea HMG-I/Y gene in tobacco containing a chimeric gene fusion of a promoter from the PR gene, DRR206, and the beta-glucuronidase (GUS) reporter gene. Transient expression of pea HMG-I/Y led to a decrease in GUS reporter gene activity in the heterologous tobacco system. These data implicate pea HMG-I/Y abundance in the down-regulation of DRR206 gene expression, and possibly HMG-I/Y depletion in the expression of defence genes in pea.