New state of immunity
Plants don’t have traveling immune cells. Therefore in case of an infection pant cells put on their own defence. Now a group of American researchers show in Nature that in plants during an infection a group of cells reprogram themselves into immune cells.
There is lots of knowledge about how a plant initiates an immune response after an infection. But till now it was unclear which cell does what. This is mainly has an technological origin. Until recently it was not possible to distinguish and follow genes and proteins at large scale at single cell level. During sampling of the infected tissue a researcher samples often multiple cell types.
With the development of single-cell-sequencing techniques this changed. In order to study which cell types initiate an immune reaction, the researchers infected leaves with immune response repressing or triggering bacteria. Subsequently the researchers sampled those leaves at different times after infection. This was followed by the separation of the cells from the sampled leaves and identifying the active genes.
During an infection cells specialise to perform different parts of the immune response
After identifying the active genes the researchers grouped the cells based on so called marker-genes for specific cell-types. Getting groups for vascular cells, epidermis cells and mesophyll cells. The researchers noticed that for some cell types there was a group with and without active immune genes.
But in order to fish out all groups of cells in with an immune response, the researchers further divided the groups in subgroups. Thereby they noticed that there was a subgroup of vascular cells that worked on sending an immune readiness signal to the rest of the plant.
Although this all gave the researchers a lot of new information, it did not tell the researchers where in the leaf relative of the infection site the cells that showed an immune response were located. To be able to do this the researchers turned to a different technique.
With this they localised for 500 selected genes were in the leaves they were active. This the researchers did for both infected and non-infected leaves.
Directly at the site of infection cell reprogram themselves into a PRIMER-state
Subsequently the researchers combined the results of those two big experiments. Based on were those 500 selected genes were active in the leaf, the researchers could determine for each subgroup from the first experiment were they were situated in the leaf.
One of the interesting things the researchers observed was that around the site of infection there are two circles of cells. The inner most circle of cells, directly around the site of infection, the researchers called PRIMER-cells. In those cells there are genes activated who are known to work immune repressive. It is not yet completely clear what those PRIMER-cells exactly do. But their main function appear to initiate the defence in the cells directly surrounding them. Those are the cells in the outside ring of cells, the so called bystander cells. Those cells are busy with warning the rest of the plant for the infection.
The researchers show that plants during an infection reprogram cells at the side of the infection into two different types of immune cells. Each with their own task. But this study also contains a wealth of information, for researchers to further analyse, about how plants regulate this.
Literature
Nobori, T., Monell, A., Lee, T.A. et al. A rare PRIMER cell state in plant immunity. Nature (2025). https://doi.org/10.1038/s41586-024-08383-z
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