CLAVATA pathway roles in Physcomitrium patens development

Abstract

Growth in land plants is based on stem cell activity. In seed plants, most of the biomass is produced in the sporophytic generation by stem cells that are embedded in complex multicellular meristems. The CLAVATA pathway is composed of a set of diffusible peptides and their receptors, and mediates intercellular communication and stem cell regulation in multicellular meristems. In non-seed plants, growth is based on the activity of one or a few apical initials. Moss development is based on several single celled meristems, each one constituted by a different stem cell type, which generate filaments, shoots, phyllids and reproductive organs in the gametophytic generation. In this thesis I explore the role of the CLAVATA pathway in the regulation of different types of moss stem cells, using the model moss Physcomitrium patens. By using expression pattern and mutant phenotype analyses, I contribute to uncover the conserved role of CLAVATA in repressing stem cell identity and/or proliferation in P. patens shoots. I then focus on the roles of CLAVATA in the regulation of plant shape and filament development. Here I show that CLAVATA represses the transition from photosynthetic (chloronema) to foraging (caulonemata) filaments by acting on apical stem cell identity. Because this identity shift is controlled by auxin and cytokinin, I then examine the links between CLAVATA and these two hormones, showing that CLAVATA upregulates auxin synthesis and transport in filaments. Finally, I examine CLAVATA roles in the regulation of bud and phyllid development, and reveal a possible role in reproductive development. Overall, in this thesis I show how CLAVATA pathway regulates different stem cell types in P. patens, and identify possible links with auxin and cytokinin homeostasis. This study will help to elucidate how single celled meristems function and how different evolutionary trajectories mold the function of gene families.

Date of Award	24 Jun 2021
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Jill Harrison (Supervisor) & Keara A Franklin (Supervisor)