An evolutionary and functional genomics study of Noccaea caerulescens, a heavy metal hyperaccumulating plant species

Noccaea caerulescens is the only known Zn/Cd/Ni hyperaccumulator. The Ganges accession (2n = 14) has an, yet unpublished, genome size of ~319 Mb, with 29,712 predicted genes representing 15,874 gene families. This species is distributed mainly in Europe. Three ecotypes can be distinguished: two metallicolous ecotypes, resident to serpentine soil (Ni enriched) and calamine soil (Zn/Cd enriched), and a non-metallicolous ecotype, growing on regular, non-metalliferous soils. The physiological differences that underlie variation in heavy metal accumulation and tolerance are well-understood, and the molecular basis of hyperaccumulation and tolerance has been explored by transcript profiling in the presence of metals and by comparative transcriptome analysis using N. caerulescens and non-hyperaccumulators such as Arabidopsis thaliana. The genetic variation which emerged during the evolution of metal hyperaccumulation has not yet been investigated. The work described in this thesis considers the identification of genetic variation under selection for Zn/Cd hyperaccumulation and tolerance by next generation resequencing of the wild metallicolous (calamine) and non-metallicolous populations and the generation of a mutant N. caerulescens library for functional analysis. The regulation of flowering time was also investigated, using early flowering mutants selected from the mutant library.