In Posidonia oceanica cadmium induces changes in DNA methylation and chromatin patterning

TLDR

In mammals, cadmium is considered a non‑genotoxic carcinogen that acts through methylation‑dependent epigenetic mechanisms. This study examines how cadmium affects DNA methylation patterns and chromatin reconfiguration in *Posidonia oceanica*. DNA methylation levels and patterns were assessed in actively growing organs after short‑ and long‑term exposure to low and high Cd doses using Methylation‑Sensitive Amplification Polymorphism and immunocytology, while CMT expression was quantified by qRT‑PCR and chromatin ultrastructure examined by transmission electron microscopy. Cadmium induced DNA hypermethylation, up‑regulation of CMT, progressive heterochromatinization, and apoptosis, demonstrating that Cd perturbs DNA methylation via a specific methyltransferase and alters chromatin to shift gene expression balance, providing an epigenetic basis for its toxicity in plants.

Abstract

In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting through a methylation-dependent epigenetic mechanism. Here, the effects of Cd treatment on the DNA methylation patten are examined together with its effect on chromatin reconfiguration in Posidonia oceanica. DNA methylation level and pattern were analysed in actively growing organs, under short- (6 h) and long- (2 d or 4 d) term and low (10 μM) and high (50 μM) doses of Cd, through a Methylation-Sensitive Amplification Polymorphism technique and an immunocytological approach, respectively. The expression of one member of the CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an up-regulation of CMT, indicating that de novo methylation did indeed occur. Moreover, a high dose of Cd led to a progressive heterochromatinization of interphase nuclei and apoptotic figures were also observed after long-term treatment. The data demonstrate that Cd perturbs the DNA methylation status through the involvement of a specific methyltransferase. Such changes are linked to nuclear chromatin reconfiguration likely to establish a new balance of expressed/repressed chromatin. Overall, the data show an epigenetic basis to the mechanism underlying Cd toxicity in plants.