A flood of calcium surrounds plants’ stomata triggering them to close and resist pathogens; exactly how calcium entered cells remained unclear until now
A new discovery related to plants’ defence mechanisms against pathogens has the potential to pave the way for healthier, more resistant and productive crops. Plants have a unique ability to safeguard themselves against pathogens and resist infection: A flood of calcium surrounds their pores — or stomata — triggering them to close. This much was known by scientists, but it was unclear exactly how calcium would enter the plant cells.
A study by an international team of scientists — including those from the University of Maryland (UMD), United States — claimed this to be the work of a protein called OSCA1.3 that formed a channel leaking calcium to the cells. A known immune system protein triggered this process as well, said the study published in journal Nature August 26, 2020.
“This is a major advance, because a substantial part of the world’s food generated by agriculture is lost to pathogens,” said José Feijó, a professor of cell biology and molecular genetics at UMD and co-author of the study. “We now know the molecular mechanism behind one of the first and most relevant signals for plant immune response to pathogens — the calcium burst after infection,” Feijó added.
The stomata are encircled by two guard cells that respond to the calcium signals telling them to either expand or contract, triggering innate immune signals and initiating the plants’ defense response. The calcium could not directly pass through guard cell membranes, so scientists knew there was a calcium channel, but did not know which protein acted to form one.
The study’s lead author Cyril Zipfel, a professor of molecular and cellular plant physiology at the University of Zurich, searched for proteins that could be modified by another protein named BIK1, a necessary component of the immune calcium response in plants.
The OSCA1.3 protein transformed in a very specific way when it was exposed to BIK1, suggesting it to be the calcium channel. BIK1 was activated only when plants were infected by a pathogen, further suggesting OSCA1.3 was responsible for creating the calcium channel that helps close plants’ stomata.
“In the context of plant immunity this work is particularly apt in 2020, the United Nations International Year of Plant Health,” said Zipfel.
Feijó now plans to use this new knowledge about OSCA1.3 in fresh research as well. This research will aim to determine how calcium was appropriated through evolution by all living organisms as a signaling device for information about stressors ranging from infections to climate change.
The study benefitted from collaboration of laboratories in Finland, Germany, Switzerland, the United Kingdom and the US.
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