Molecular mechanisms behind Zn and low oxygen conditions in plants

With this thesis, we expanded our knowledge about two different aspects of flooding stress in plants, which are still unexplored: the cross-talk between waterlogging and heavy metal contamination, and, on the other hand, the evolution of the molecular responses to low oxygen in land plants. As discussed above, a waterlogged soil alters the quality of nutrients available for the plant and it often increases the solubility of contaminant elements. This aspect is of great interest in phytoremediation approaches of soils enriched by heavy metals, where the solubility of the contaminants might vary upon flooding events. We chose Populus alba ‘Villafranca’ clone, a Zn-tolerant cultivar, as a model species to address this question, since its economic value in terms of phytoremediation. Starting from the observation that a common set of genes is activated upon Zn excess and waterlogging, we investigated the molecular aspects behind this cross-talk, which involved the regulation of the ERF-VII transcription factors by the N-end rule pathway. We supported our molecular results with phenotypical analyses putting forward the hypothesis that the overlap between the two responses is the consequence of a plant adaptation to foresee a worsening of the environmental conditions. Partially flooded environments characterized the first ecological niches colonized by first land plants during the switch from aqueous to dry habitats, around 480 millions of years ago. In order to understand how early land plants adapted to these challenging environments and to which extent this response evolved along plant evolution, we chose the liverwort Marchantia polymorpha as model species. We exposed Marchantia to different regimes of low oxygen conditions and we evaluated its molecular and morphological responses in response to them. We eventually discriminated between those aspects of the response to low oxygen conserved among lands plants and those which were instead acquired later during plant evolution, by higher plants.