Supple cells for growth
We don’t notice it, but the growth of organisms, organs, and tissues is strongly coordinated. Only when something goes wrong. Or, maybe we don’t, don’t see it as a mistake but a nice new trait. One of those things that need to be coordinated is growth between different tissue layers. This coordination is crucial, especially in plants where the different cell layers are connected by a cell wall. Now British and Chinese researchers show how genes can control the mechanical interactions between different cell layers.
To study this the researchers turned to floating bladderwort, a small floating water plant with long thin steles and thread like leaves. And to be more precise, they looked at bladderwort plants that developed less well, and had short steles. These short steles they compared with the steles of normally developing plants. Where, in the normally developing steles, the researchers observed lots of empty spaces intersected by cell like the empty spaces between the spokes of a wheel. In the short steles, the empty spaces were smaller, with bended spokes.
To find a possible reason for this particular observed phenotype, the researchers turned to computer simulations. This allowed them to study the effect of the difference in growth and pressure between the different cell layers. They noticed that the twisting, the bended spokes, observed in plants with short steles occurs when the outer layer of the stele does not grow.
Brassinosteroid give the cells a less tight corset
Subsequently the researchers looked to the genetic differences between the normal and short bladderwort plants. Here the researchers stumbled on differences in the gen DWARF. This is a gene that codes for an enzyme needed to produce brassinosteriod. And indeed, when the researchers grew the short bladderwort plants in presence of brassinosteroid, those plants developed like normal bladderwort plants.
Now the big question was how brassinosteroid enables normal growth. A hint came from the influence of brassinosteroid on the stretching of a just germinated seedling. Here brassinosteroid enables the cell walls stay supple. To test this, the researchers put this information in to their computer simulation. And indeed, when the cells of the outer layer of the stele had souple cells, then those cells could stretch and grow along with the cells inside the stele.
Brassinosteroid gave the cells a less tight corset, and the space to move along with its neighbours. In absence of brassinosteroid, the corset was laced tightly , with no space for movement. Resulting in twisting and loss of hollow spaces.
Literature
Robert Kelly-Bellow et al., (2023) Brassinosteroid coordinates cell layer interactions in plants via cell wall and tissue mechanics. Science380,1275-1281. DOI: 10.1126/science.adf0752
Plant en Zo 