Three ancient hormonal cues co-ordinate shoot branching in a moss.

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Coudert, Yoan 
Palubicki, Wojtek 
Novak, Ondrej 
Leyser, Ottoline 

Shoot branching is a primary contributor to plant architecture, evolving independently in flowering plant sporophytes and moss gametophytes. Mechanistic understanding of branching is largely limited to flowering plants such as Arabidopsis, which have a recent evolutionary origin. We show that in gametophytic shoots of Physcomitrella, lateral branches arise by re-specification of epidermal cells into branch initials. A simple model co-ordinating the activity of leafy shoot tips can account for branching patterns, and three known and ancient hormonal regulators of sporophytic branching interact to generate the branching pattern- auxin, cytokinin and strigolactone. The mode of auxin transport required in branch patterning is a key divergence point from known sporophytic pathways. Although PIN-mediated basipetal auxin transport regulates branching patterns in flowering plants, this is not so in Physcomitrella, where bi-directional transport is required to generate realistic branching patterns. Experiments with callose synthesis inhibitors suggest plasmodesmal connectivity as a potential mechanism for transport.

Physcomitrella, apical dominance, branching, developmental biology, gametophyte, plant biology, stem cells, Biological Transport, Body Patterning, Bryopsida, Cytokinins, Gene Expression Regulation, Plant, Indoleacetic Acids, Lactones, Models, Biological, Morphogenesis, Mutation, Plant Epidermis, Plant Growth Regulators, Plant Proteins, Plant Shoots, Plants, Genetically Modified
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eLife Sciences Publications, Ltd
Biotechnology and Biological Sciences Research Council (BB/L002248/1)
European Research Council (294514)
We thank Catherine Rameau, Eva Sundberg and Klaus von Schwartzenberg for giving us mutant lines, Nik Cunniffe for his support with statistical analyses and Siobhan Braybrook for help with the scanning electron microscope. We thank our funding bodies for financial support. Yoan Coudert and Jill Harrison are funded by a BBSRC grant ‘PIN proteins and architectural diversification in plants’ (Grant BB/L00224811) and fellowships from the Gatsby Charitable Foundation (GAT2962) and Royal Society. Ottoline Leyser and Wojtek Palubicki are funded by the Gatsby Charitable Foundation (Grant GAT3272C) and by the European Research Council (Grant N° 294514—EnCoDe). Karin Ljung is funded by the Swedish Governmental Agency for Innovation Systems (VINNOVA) and the Swedish Research Council (VR) and thanks Roger Granbom for excellent technical assistance. Ondrej Novak is funded by a Czech Ministry of Education grant from the National Program for Sustainability I (LO1204).