Deciphering stress reactions
At first glance a plants reaction to many stressors appear to be identical. Still each stressor elicit a specific response. Now German researchers show in Nature using light-gated calcium and anion channels that the difference is in the tiniest detail of the reaction.
In studies with animal cells, researchers are using them for some time. Light sensitive proteins, that enable researchers to use light signal tell cells what to do. But recently researchers figured out how to use them to study plants without interfering with normal plant growth.
For the recently published study the researchers used two light sensitive channels. The first channel, XXM, allows by green light calcium ions into the cell. The second channel, ARC1, allows by green light anion ions out of the cell. Both cause an electric current to move over the cell membrane.
The effect that both light sensitive channels have on the plants is completely different. The leaves, of plants in which XXM is turned on, die. This the researchers could prevent by giving the plant a calcium ion binding substance. In contrast, the leaves, of plants is which ARC1 is turned on, wilt as if they did not got enough water. Turning off the green light allowed the plants to recover.
Minute differences in initial stress responses cause different reactions
Subsequently the researchers measured the amount of stress hormones the plant produces. In plants in which XXM in turned on, jasmonic acid and salicylic acid were more abundant. Both hormones are involved in the regulation of pathogen defence. In plants in which ARC1 is turned on the drought response hormone, ABA, is more abundant.
Finaly the researchers analysed which genes were turned on or off as a result of the turning on one of the light sensitive channels. This, it turned out, were a lot. Detailed analysis confirmed the earlier findings: the combination of a membrane current and increased calcium concentration activates pathogen responses. While is there only a membrane current, then drought stress reaction is activated.
With this study the researchers have taken the first step in the deciphering of how a plant knows which stress response to activate. Up till now the initial response appeared to be identical, but through use of these two light sensitive channels the researchers show that there are minute differences. In this study the light signal the researchers used activated the light sensitive channels in the whole plant. But in future studies the light signal can be focussed on a few cells, the researchers say, so they might study local effects.
Literature
Ding, M., Zhou, Y., Becker, D. et al. Probing plant signal processing optogenetically by two channelrhodopsins. Nature (2024). https://doi.org/10.1038/s41586-024-07884-1
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