The role of cell geometry, growth and mechanics in plant cell division.

• Applicant: Dr. Richard S Smith
• Subject Area: Plant Cell and Developmental Biology
• Term: from 2017 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 318879394

Since plant growth is symplastic, plants must create their form by precisely regulating cell growth and division. It has been proposed that plants have default rules for symmetric cell division, defined as divisions where the daughter cells have the same fate. Proposed rules have been based on the geometry of the cell, growth directions, or mechanical stresses, although none of these seems able to capture plant-wide cell behaviour. Since these factors are interrelated, it seems likely that there is an underlying default rule for all cells, and the differences observed are due to different growth rates, the mechanical environment perceived by the cell or other parameters. It has also been reported that non-symmetric or formative divisions often do not follow the default rule, and that there is an association between geometric asymmetry and daughter cell fate asymmetry.  In this project we will use a computational morphodynamics approach to quantify growth and cell division in 3D, to determine which parameters the cell is using to orient division. We will build a 3D mechanical model of the tissue under study, in order to determine the stresses that cell perceives, and how these may be integrated into the determination of division plane orientation. We will then extend the model to understand how rules might be modified for formative divisions.We will primarily use two biological systems developed by other partners in the RU. The emergence of Arabidopsis lateral root is the focus of the Maizel lab, and the development of the Arabidopsis ovule and integuments is the focus of the Schneitz lab. Both are good systems to study primary morphogenesis, as they begin with relatively few cells, have variable and often highly anisotropic growth, and result in the specification of non-trivial shapes with several different cell types. The systems show promise for full 3D imaging, and in the case of lateral root emergence, full 3D time-lapse. We will use these systems to determine the default rules for cell division in the Arabidopsis lateral root and the ovule, with the goal to unify the many different but seemingly related division rules proposed previously. We will investigate how formative divisions can be integrated into the model, and whether they are just a straightforward variation of the underlying mechanism. We will also investigate the relationship between geometry asymmetry and fate asymmetry in these systems.

• DFG Programme: Research Units
• Subproject of: FOR 2581: Quantitative Morphodynamics of Plants