Plant & zo
The science of plants and more
Loss of pressure
The epidermis, the outer cell layer of a plant, protects the plant against the outside world. Their function is determined by their position in the plant. All cells in the outermost cell layer are doomed to develop into epidermis cells. Up to now it was unknown how these cells recognise their position. Now Japanese, Finnish, and German researchers have discovered that the amount of pressure a cell experience determines if they turn on the epidermis master switch ATML1.
ATML1 is a transcription factor, a gene on/off switch, that turns on the genes needed for a cell to develop into an epidermis cell. ATML1 is switched on in all the epidermis cells, but not in the underlying mesophyll cells. But what causes ATML1 to be turned on in this outermost cell layer was unknown.
In order to study this the researchers analysed ATML1 expression after they made a new the outer layer of a leaf through stripping it from its epidermis. They observed that in the exposed outside mesophyll cells ATML1 was switched on. But only in these cells. In a lower cell layer ATML1 was off.
ATML1 was only switched on in epidermis stripped leaves in low osmolarity
The researchers noticed that the exposed mesophyll cells extruded from the leaf. This gave them the hind that a difference of pressure might be playing a role in turning ATML1 on. To analyse this, the researchers placed an epidermis stripped leaf artificial under pressure through placing it between to glass coverslips. Looking how this affected ATML1 expression, the researchers observed that the mesophyll cells with the artificial epidermis did not turn on ATML1. But in absence of the artificial epidermis ATML1 was switched on in the exposed cells.
Subsequently the researcher confirmed that it was indeed the pressure difference that turned on ATML1. For this they placed epidermis stripped leaves in solutions with different osmolarity. Cells in a high osmolarity solution would not feel the otherwise perceived pressure difference, while those in a low osmolarity solution do. The researchers observed that ATML1 was only switched on in epidermis stripped leaves in the low osmolarity solution.
The registration of the loss of pressure on the mesophyll cells result in the switching on ATML1. But how the cell exactly perceives this loss of pressure is still unknown. But the first step is taken in finding out how this is done.
Iida, H., Mähönen, A.P., Jürgens, G. et al. (2023) Epidermal injury-induced derepression of key regulator ATML1 in newly exposed cells elicits epidermis regeneration. Nature Communications 14, 1031. https://doi.org/10.1038/s41467-023-36731-6