Plant & zo
The science of plants and more
Finding balance
Miraculous, when you start thinking about it. Each plant, from the tiniest tot the gigantic, grow from their growth regions. Small groups of cells with as main goal: slowly dividing and no specialisation. By each division these cells place their daughter cells outside their group. These then divide a few more times and slowly specialise. Into vascular tissue for example. Fascinating though is how the group of cells in the growth region stays the same.
Different genes have a role in this. And for the root growth region, the accumulation of the plant hormone auxin decides the place of the growth region through turning on the necessary genes. But the gene-on switches WOX5 and BRAVO decide which cells are part of the growth region. Through turning on the genes needed for division and keeping off those genes required for specialisation. When they can’t do their work properly, for example through a mutation, then the growth region cells divide more often. Then the size of the growth region changes.
Balance, while WOX5 and BRAVO control each other
Spanish researchers studied how WOX5 and BRAVO manage this. They did this using a computer simulation. These they compared with real life observations. Where these comparable, then the assumptions of the simulation were probably correct. With as result a model.
In the plant, the WOX5-gene is only on in the cells of the growth region. But the WOX5-protein can get into its neighbouring cells. One of the genes that is turned on via WOX5 is BRAVO. Therefore, the BRAVO-gene is also on in the neighbouring cells of the growth region. But in contrast to the WOX5-protein, the BRAVO-protein can’t get into its neighbouring cells. To prevent the WOX5-protein from wandering to far from the growth region, the BRAVO-protein is holding on to the WOX-protein every time they meet. In doing so BRAVO prevents expansion of the growth region.
However, if BRAVO is catching off all the WOX5-protein, then WOX5 can’t do its job of turning on genes. Therefore, WOX5 by itself is not turning BRAVO on, but it uses a messenger. Turning BRAVO on for WOX5. But BRAVO, in turn, is turning off the messenger. In this way WOX5 prevents shrinking of the growth region. An equilibrium establishes. Through WOX5 and BRAVO controlling each other, the number of cells in the growth region stays the same.
Literature
Josep Mercadal, Isabel Betegón-Putze, Nadja Bosch, Ana I. Caño-Delgado, Marta Ibañes (2022) BRAVO self-confined expression through WOX5 in the Arabidopsis root stem-cell niche. Development 149 (15): dev200510. doi: https://doi.org/10.1242/dev.200510
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