As many cell files need to be formed during vascular development, it is crucial to understand how plants control the orientations of their cell divisions. In this project we aim to understand this by using genetic and chemical genetics approaches.
What determines division plane orientation? Already in the nineteenth century, Errera and de Wildeman formulated rules stating that cells divide along the plane of the smallest surface that encloses a fixed cellular volume and is thus more commonly known as the ‘shortest wall’ rule. As this rule always leads to symmetric divisions, clearly it cannot explain e.g. the first division of the zygote in Arabidopsis thaliana. Nevertheless, more recent work using 3D meshes of maize cells has shown that these rules can be used to accurately predict the PPB positioning. However, 3D analysis of the Arabidopsis plant embryo has shown the phytohormone auxin is able to allow deviation from the shortest cell wall rule and change division plane orientation. Thus, it is hypothesized that this rule acts as a default mechanism of cell division orientation when internal or external cues are absent.
Ultimately deviating from this proposed ‘shortest wall’ default mechanism would require a shift in the cortical cytoskeletal organization because the PPB and finally also the actual cell plate will form in the same orientation as the cortical cytoskeleton. Therefore, in order to deviate from the shortest wall rule, a cell must receive other cues in order to position its division plane differently. These cues can be, but are not limited to, developmental programs (e.g. lateral root formation or vascular development), genetic factors (e.g. transcription factors), responses to hormones (e.g. auxin or gibberellic acid) or environmental inputs (e.g. light or mechanical pressure). Overruling the default state can be the result of only one cue or a combinatorial effect of multiple cues at the same time. While it is known that certain cues are able to overrule the default state and shift the cell division into a certain position, it remains unknown exactly how these cues determine the future division plane position and orientation. Hence, a real gap in our current understanding is how this variety of cues eventually influences the cortical cytoskeleton, which will lead to specific oriented cell divisions.
Figure: Overview of different ways a cell can position and orient its division plane and how different cues can affect cell division orientation. A. Cells can position their division plane symmetric or asymmetric which gives rise to daughter cells of the same or different size, respectively. B. Different ways how a cell can orient its division plane. Anticlinal divisions lead to more cells within a cell file. Radial cell divisions increase the amount of cell files in a within a cell type while periclinal divisions lead to additional cell files. C. Mutations in genes involved in positioning the PPB, CDZ or phragmoplast often result in perturbed division planes. D. A cell at interphase is subjected to different cues which affects how it will orient and position its array of cortical microtubules (green lines). This affects the formation of the PPB (green band) and ultimately how the daughter cells are positioned. E. An increase of a certain cue (in this case a genetic cue) can lead to reorientation of the cortical microtubule array changing the division plane orientation.
People involved in this project:
- dr. BaoJun Yang (funded by ERC starting grant)
- dr. Jos Wendrich (funded by ERC starting grant)
- dr. Matouš Glanc (funded by ERC starting grant)