Directing cell divisions
Multicellular organisms come in lots of different forms and shapes. Al coming from the same invention: RHO GTPases, proteins that give a cell its polarity. Now a team of Austrian researchers show in Current Biology that the plant specific RHO GTPase, ROP, is required for both the polarity and orientation of cell division.
Without influence on polarity and orientation cell divisions can only result in multicellular blobs. The large diversity of multicellular organisms indicates that polarity and orientation do influence cell divisions. One of the proteins that influences this in plants are ROPs. But it is difficult to study how far the influence of ROPs reach, as most plants have multiple ROPs compensating for each other when one of them falls away. That’s why the researchers turned to the liverwort Marchantia polymorpha, which has only one ROP.
After studying liverworts without ROP, the researchers noticed multiple miss formed organs. The air holes, for example, were missing their roof. Subsequently the researchers analysed the precise location of ROP during the development of these air holes.
By simply giving polarity to cells, ROPs influences the shape of an orgainism
They observed that cell membranes at the side of the future daughter cell collected ROP proteins. Moreover, ROP proteins were also present there were the new cell wall was created. This suggests that ROP makes sure that cell divisions take place in a specific orientation and (a)symmetry. Enabling the formation of tent like structures, the air holes.
In absence of ROP, the researchers noticed, that the plant is unable to for the roof of the tent. Studying the cell divisions, the researchers observed that the cells did not divide asymmetrically. This prevented them to make the kind of sidewards cell divisions that are required for forming the roof.
In this way a single ROP, by giving cells polarity, can influence the shape of an organism. With multiple ROPs, the cell shape itself, and that of the whole organism can even more precisely be influenced. And in the case of a ROP gene failing, other ROPs can prevent that the final shape diverges to far from what was planned.
Literature
Mulvey, Hugh et al. (2023) RHO GTPase of plants regulates polarized cell growth and cell division orientation during morphogenesis. Current Biology, 33 (14), 2897 – 2911.e6 https://doi.org/10.1016/j.cub.2023.06.015
Plant en Zo 