Evolution of the regulatory networks governing developmental adaptations and acclimation responses in Charophycean green algae towards plant life on land

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Plants differentiate specialized cell types, tissues, and organs that are fundamental to their photosynthetic lifestyle and for thriving in their respective ecological niches. All differentiated cells ultimately descend from stem cells, undifferentiated, pluripotent progenitors. During ontogenesis, small groups of stem cells are maintained at certain positions, the so-called stem cell niches. Such niches exist in plants within the root, shoot and vascular meristems. In these stem cell niches, a precisely balanced set of regulatory factors ensures that the undifferentiated, pluripotent state is maintained, while cells at the periphery are able to enter specific differentiation pathways. To control cell differentiation status, plants possess multiple mechanisms that include specialized transcription factors and microRNAs. Our key hypothesis is that the mechanisms underlying the complex land plant morphologies evolved in specific members of the charophytes, and that by characterization of specific regulators’ molecular functions it is possible to track the evolutionary process. Therefore, this project follows the hypothesis that the emergence of these regulatory mechanisms was of central importance in early land plant evolution. We will focus on the Chara braunii model but compare to insight obtained in other algae and land plant models such as Arabidopsis and Physcomitrium. In Chara braunii, nodal central cells are candidates for pluripotent cells, which will be characterized at single-cell level. We will then investigate the role of certain regulators in controlling cellular and chloroplast differentiation and follow the regulatory responses to selected abiotic stresses. While the focus is on charophytes, the systematic comparison with data from mosses and ferns will advance, based on publicly available datasets and in particular through collaborations within the SPP. In addition, we will provide bioinformatics expertise for the analysis of gene expression datasets and RNA:RNA interactions and Chara braunii material and cultures, thereby strengthening the know-how of the consortium as a whole.