Autoimmune plants
By autoimmunity the immune system is turned on to quickly. Now American researchers show in Nature Plants that for some plants that show autoimmunity this is because they also react to harmless bacteria.
Plants in which their immune system is activated while there are no pathogens are autoimmune. They are smaller and their leaves show yellow or dead spots. And although there are no pathogens, a whole scala of other non-pathogenic bacteria are living on and in those plants. The researchers decided to study the influence of these bacteria on the immune system.
Firstly they searched for a mutant that reacted differently to the bacteria living on their leaves. The researchers found this in a plant that did not make the protein TIP1. These plants were smaller, had lots of yellow spots on their leaves and curiously, one bacteria family was dominating the bacteria on their leaves. And just like by other autoimmune plants, the genes for defence were constantly on.
There are at least two ways of autoimmunity
But when comparing to other autoimmune mutants, the researchers noticed something different. In contrast to lost of other autoimmune mutants, the autoimmune symptoms of TIP1-less plants disappeared when they grew in a environment without bacteria. Then TIP1-less plants did just as good as TIP1-containing plants. A subsequent analysis the researchers found two other autoimmune mutants that also grew normal in a bacteria free environment.
This was reflected in the genes that are active in the TIP1-less plants. When they grow in a bacteria free environment, then these are comparable to TIP1-containing plants. But in an environment with bacteria, then the genes that are active showing more overlap with those of other autoimmune mutants.
The autoimmunity of TIP1-less plants is probably due to that they also react to the non-pathogenic bacteria that grow on their leaves. They assume that these are pathogenic, and turn on their immune response. Why exactly this happens, and what TIP1 does; that the researchers are studying next.
Literature
Cheng, Y.T., Thireault, C.A., Zhang, L. et al. Roles of microbiota in autoimmunity in Arabidopsis leaves. Nat. Plants 10, 1363–1376 (2024). https://doi.org/10.1038/s41477-024-01779-9
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