Abstract
The mechanistic understanding of metal hyperaccumulation has benefitted immensely from the use of molecular genetics tools developed for Arabidopsis thaliana. The revolution in DNA sequencing will enable even greater strides in the near future, this time not restricted to the family Brassicaceae. Reference genomes are within reach for many ecologically interesting species including heterozygous outbreeders. They will allow deep RNA-seq transcriptome studies and the re-sequencing of contrasting individuals to unravel the genetic basis of phenotypic variation. Cell-type specific transcriptome analyses, which will be essential for the dissection of metal translocation pathways in hyperaccumulators, can be achieved through the combination of RNA-seq and translatome approaches. Affordable high-resolution genotyping of many individuals enables the elucidation of quantitative trait loci in intra- and interspecific crosses as well as through genome-wide association mapping across large panels of accessions. Furthermore, genome-wide scans have the power to detect loci under recent selection. Together these approaches will lead to a detailed understanding of the evolutionary path towards the emergence of hyperaccumulation traits.
Highlights
To maintain concentrations of essential metals within physiological limits and to cope with toxic non-essential metals, plants possess a sophisticated and tightly controlled metal homeostasis network that insures the balance between metal uptake, chelation, distribution and storage processes
Understanding hyperaccumulation offers the promise of uncovering key nodes of the metal homeostasis network whose alterations can drastically modify metal accumulation and tolerance in plants
In A. halleri, recent adaptations to anthropogenic metallic excess may have independently occurred within distinct phylogeographic units, which potentially have involved the evolution of a variety of genetic mechanisms (Pauwels et al, 2012)
Summary
To maintain concentrations of essential metals within physiological limits and to cope with toxic non-essential metals, plants possess a sophisticated and tightly controlled metal homeostasis network that insures the balance between metal uptake, chelation, distribution and storage processes. Understanding hyperaccumulation offers the promise of uncovering key nodes of the metal homeostasis network whose alterations can drastically modify metal accumulation and tolerance in plants This knowledge could be used to develop biotechnological tools for biofortification and phytoremediation strategies. Research on A. halleri and N. caerulescens has been following similar trends than in A. thaliana going from a candidate gene approach in a limited number of ecotypes to genome-wide studies in a vast range of natural accessions. Tapping into natural diversity of plant phenotypes will reveal commonalities and differences in the adaptation of the metal homeostasis networks that support hyperaccumulation and tolerance In this perspective note, we will highlight what can be expected from the use of NGS technologies to examine metal tolerance and accumulation mechanisms in hyperaccumulators (Figure 1).
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