Ecophysiology and genetic analysis of plant adaptation to soil metal contamination

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High soil metal levels may seriously threaten ecosystem sustainability. Physiological and genetic mechanisms regulating metal accumulation and resistance in plants are complex. Our understanding of plant responses to metal toxicity is poor despite recent uses of high-throughput methods. This research program will provide new insights on how key non-model plant species (useful in bioremediation) cope with high soil metal levels. The four parts (objectives) address four linked issues: 1) how plants cope with metals using genetic and comparative transcriptome analyses; 2) the cellular and extracellular locations and the transport proteins involved; 3) the levels and distribution of cytosine methylation in response to metal contamination; and 4) the link between DNA methylation and gene regulation in response to metal toxicity. We first demonstrated that, to cope with metals: 1) Acer saccharinum (silver maple) excludes them; 2) Populus tremuloides (trembling aspen), Betula papyrifera (white birch), and Quercus rubra (red oak) accumulate them; and 3) Acer rubrum (red maple) avoids them. Importantly, we completed and characterized the first transcriptome of B. papyrifera and identified six candidate nickel resistance genes therein. Recently, we characterized horizontal gene transfer of nickel resistance in the Genus Betula. We believe combining approaches will provide the most robust way of elucidating plant:metal coping mechanisms. Comparative analysis of A. rubrum, A. saccharinum, B. papyrifera, P. tremuloides, and Q. rubra, using genetic analysis, transcriptome sequencing, and RT-qPCR will identify functional gene-sets differentially regulated in response to high nickel (Ni) and copper (Cu). Distribution of novel genes associated with Ni/Cu resistance in other plants in Canada and elsewhere will be established. Fluorescence in situ, protein characterization, and electron microscopy techniques will establish cellular and extracellular distribution maps and clarify the main effects of Ni and Cu and involved transport proteins. Methylation sensitive amplified polymorphism (MSAP) analysis and bisulfite sequencing will assess the role of epigenetics in plant:metal responses. Not only correlations between DNA methylation and gene expression at the methylome/transcriptome scale, but also the link between DNA methylation and regulation of gene response to Ni/Cu contamination, will be established. Our research program will help understanding of how heavy metal homeostasis is achieved, and the role of different genes, in the operation of transporters in different species that may differ greatly in metal accumulators and excluders. Our achieved goals will address several fundamental plant:metal interaction issues directly applicable to important bioengineering or plant selection strategies. Six graduate, four undergraduate, and summer students will be trained, to fill this void in biotechnology in Canada, in this phase.