Calcium channels prohibit pathogen entry

-Binayak Das, Team bioXone

Stomatal cells help plants to breathe and facilitate the vital process of photosynthesis by allowing gaseous exchange between the plant and the atmosphere. They also are highly involved in responses to various environmental stress cues and do so by controlling the closure of these cells, the mechanism of which is largely based on the movement of Ca²⁺ ions via various designated calcium channels present across the cell’s plasma membrane.

Recently, it has been observed in the model plant Arabidopsis, that two such gated calcium channels, namely OSCA1.3 and OSCA1.7, were able to prohibit the entry of pathogens by rapidly closing its stomatal pores.

It was seen that upon a perception of a bacterial flagellin protein, known as flg22 on the cell exterior surface, a complex structure is formed inside the guard cell’s cytoplasm, which is composed of- flg22, bound to cell receptor FLS2, BAK1 protein, BIK1 protein, and a phosphate molecule that is attached to BIK1. BIK1 then proceeds to phosphorylate the OSCA Ca²⁺ channel, resulting in the closure of the pores, thereby establishing stomatal immunity.

Although the exact mechanism for the closure is not yet known, one possibility proposed by the author says that certain enzymes called CDPKs are able to influence a process that causes removal of several anions, and that parallelly causes water loss also, thereby closing the guard cells.

Such findings simply go on to shed more light on how fascinating plants really are and also help us increase the possibilities of bioengineering various crucial plants in the near future, in order to save them from adverse environmental factors that endanger them.

Source:

1. Calcium channel helps shut the door on intruders, Keiko Yoshioka & Wolfgang Moeder, NEWS AND VIEWS, https://www.nature.com/articles/d41586-020-02504-0
2. The calcium-permeable channel OSCA1.3 regulates plant stomatal immunity, Thor, K., Jiang, S., Michard, E. et al.  Nature (2020). https://doi.org//10.1038/s41586-020-2702-1