Long lasting effects of cell divisions
Lots of organisms show one or more forms of symmetry, plants included. In The Plant Journal English researchers show that this symmetry starts by cel divisions.
Because of their cell wall plant cells can not move from their location. Therefore how and when a cell divides in part influences the shape of a plant. The results of lengthwise divisions is simply different form sidewise divisions. The researchers decided to find out what influences the orientation of those cell divisions.
For this they used a developing style. During development of the style the symmetry is shifting from a bilateral one to a radical one. Under normal conditions the cells keep dividing sidewise. But when the cells are missing SPT and IND then the style is splitting halfway in two. When you zoom in to the cell divisions, then it appears that in the upper half they are dividing lengthwise.
The pulsing pattern of cell cycle genes probably influences the cell division orientation
But SPT and IND are managers, they are regulating other genes. SPT it turns out regulates genes that regulate the distribution of the plant hormone auxin. From auxin, in turn, it is known that it influences the orientation of cell divisions. Under normal conditions the researchers observed that there is lots of auxin in the dividing cells of the style. But not when SPT is absent.
In the absence of SPT the cells appear to take longer for getting through the first phase of the cell division. This was due to the fact that both SPT and IND are regulating specific cell cycle genes. But, as the researchers showed, the absence of these specific cell cycle genes did not result in a split style.
In addition to SPT and IND auxin also regulates these specific cell cycle genes. Or to be more precise, it turns them off. But as SPT also regulates the amount of auxin in the cell, with as combined result: a pulsing on/off pattern for these specific cell cycle genes. The researchers expect that this pulsing pattern of cell cycle genes influences the cell division orientation. Although, more research is needed to confirm this.
Literature
Tasker-Brown, W., Koh, S.W.H., Trozzi, N., Maio, K.A., Jamil, I., Jiang, Y., Majda, M., Smith, R.S. and Moubayidin, L. (2024), An incoherent feed-forward loop involving bHLH transcription factors, Auxin and CYCLIN-Ds regulates style radial symmetry establishment in Arabidopsis. Plant J. https://doi.org/10.1111/tpj.16959
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