About this Research Topic
In the course of evolution, plants adapted to widely differing metal availabilities in soils and hence represent an important source of natural variation of metal homeostasis networks. When exposed to excess metals, most plant species adopt a so-called excluder strategy by which metals are stored in root cell wall and vacuoles, and thus kept sequestered away from shoot tissues. In contrast, a small number of plant species (~500) that live on naturally or anthropogenically metal-contaminated soils possess the ability to accumulate and tolerate extraordinarily high metal concentrations in leaves (e.g., > 1% zinc, 0.1% nickel or 0.01% cadmium in dry leaf biomass). Most hyperaccumulator species hyperaccumulate nickel, but hyperaccumulation of zinc, manganese, copper, cadmium, lead, selenium or arsenic also occurs in several species. Metal hyperaccumulators constitute fascinating models to study adaptations to hostile environments and the evolution of a naturally-selected complex trait. In addition, metal hyperaccumulators also attract interest as they represent the 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. This knowledge can then be applied to develop biofortification and phytoremediation strategies.
Thanks to their close relationship with Arabidopsis thaliana, the Brassicaceae Noccaea caerulescens and Arabidopsis halleri, two zinc and cadmium hyperaccumulators, represented in the last decade models for the functional analysis of metal hyperaccumulation and hypertolerance. The recent boom of 'omics' technologies now permits to expand those analyses to many more species. Ongoing investigations in the field are aiming to uncover the biochemical and physiological mechanisms underlying metal hyperaccumulation, and to determine how the trait evolved by analyzing phylogeography of the species, population history or the determinants of intraspecific variation, or by identifying loci that have been under selection. Studying the interactions of metal hyperaccumulators with their biotic environment (i.e. with microorganisms in the rhizosphere, or with herbivores and pathogens) is also highly relevant.
This Research Topic will highlight how metal hyperaccumulation and associated hypertolerance are examined using a combination of physiology, functional genomics, quantitative genetics, evolutionary ecology and population genomics approaches to reveal the molecular basis of adaptation. We warmly welcome original research articles, method articles, reviews, mini-reviews or perspective articles.
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