Cell markers for air chamber development in Marchantia polymorpha

Marchantia polymorpha, thanks to its small genome and its simple cellular architecture, is an excellent model for the study of developmental processes. Marchantia can propagate asexually producing small flat disc-like propagules, called gemmae, that develop into adult plants. Gemmae have an open mode of development, which facilitates the live observation of developmental processes. The fundamental processes underlying morphogenesis in plants are poorly understood and epidermal patterning represents one of the key events during plant development. Marchantia produces characteristic epidermal structures called air chambers that represent an example of a self-organising, three-dimensional morphological unit that has a modular and repetitive arrangement, similar to the one observed in stomata meristemoid cells in vascular plants. To date, the cellular scale and the genetic description of air chamber development are poorly resolved. Therefore, in this dissertation I applied modern genetic and microscopy tools to better map the process of air chamber morphogenesis at a cellular scale and to generate genetic markers to understand the steps involved in this developmental process. Similar tools have been used in Arabidopsis thaliana, and they have shown that patterning and cell differentiation can be dissected into discrete steps that provide insights into the mechanisms controlling the process and can also represent valuable targets for engineering the entire process. In my thesis, I developed high resolution imaging techniques to produce a systematic description of air chamber development. I generated genetic resources to identify potential candidate genes involved in air chamber development by comparing the transcriptome of wild type plants and the nopperabo1 (nop1) mutants that are unable to produce air chambers. Candidate genes were used to build a collection of cellular markers to be screened for their potential involvement in air chamber patterning. The screening led to the identification of two potential transcription factors, MpbHLH24 and MpWRKY10.