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    A Key Link in the Immune Response of Plants

    08/26/2020

    Plants can defend themselves against harmful fungi and bacteria. An international research team describes in the journal "Nature" the signal chain with which they react to such dangers.

    Um zu vermeiden, dass Krankheitserreger (grün) durch die Spaltöffnungen in die Pflanze gelangen, werden diese geschlossen. Dabei erkennt der Rezeptor FLS den Erreger und öffnet den Ionenkanal OSCA, der Kalzium in die Zelle strömen lässt. Das Kalzium aktiviert eine Kinase (CPK), die dann den Anionenkanal SLAC öffnet. Der initiiert das Schließen der Spaltöffnungen.
    To prevent pathogens (green) from entering the plant through the stomata, these pores are closed. The receptor FLS recognises the pathogen and opens the ion channel OSCA, which allows calcium to flow into the cell. The calcium activates a kinase (CPK), which then opens the anion channel SLAC. This initiates the closing of the stomata. (Image: Sönke Scherzer / Universität Würzburg)

    Just as humans, plants need to defend themselves against a broad spectrum of microorganisms. The disease-causing bacteria and fungi utilize small pores in the leaf surface, known as stomata, to invade plants. Plants can close their stomata if they are threatened by pathogens, but not permanently: they need open pores to absorb carbon dioxide from the environment for photosynthesis.

    The mechanism by which plants recognise their enemies and then close the bulkheads is indispensable for their survival under natural conditions. Professor Rainer Hedrich's research group at Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, has been studying precisely this mechanism for many years.

    Among other things, Hedrich's team has discovered how a specialized cell type – a pair of guard cells that form pores which are permeable to air and water vapor – controls the opening and closing of these pores. The SLAC1 channel in the outer membrane of the guard cells plays a central role in this process: If the calcium concentration in the cells increases, the channel release anions such as chloride from the cells. As a result, the stomata will close.

    New function of the OSCA channels discovered

    For long it has remained unclear how the calcium level in the guard cells increases in response to pathogens. A consortium, headed by Professor Cyril Zipfel from the University of Zurich in Switzerland and supported by Professor Hedrich's group, has now identified the long-sought reaction sequence that contributes to the immune response of the guard cells. The results have been published in the well-known scientific journal Nature.

    Using a new technique developed in Hedrich's lab (scanning ion selective electrodes), it turned out that two proteins of the OSCA family allow calcium ions to enter the guard cells once immune receptors on the cell surface have identified a pathogen.

    The OSCA channels were previously known to react to mechanical stimuli. In the immune response they are activated by a chemical modification. This step triggers a signalling chain in the closing cells, which runs through the channel SLAC1 and ultimately leads to the closing of the stomata. This showed that the OSCA channels play an important role in mechanical damage and in infections caused by bacteria and fungi.

    New strategies for plant breeding

    Diseases caused by bacteria and fungi can be devastating in agriculture, as they cause huge losses of crop yield and eventually may lead to famines.

    With the discovery of the role of OSCA channels in the immune response of plants, the groups of Professors Zipfel and Hedrich can now explore new strategies for breeding plants which have superior defense responses against pathogens. In agriculture, such plants should be less susceptible to disease and enable farmers to cut down the use of chemicals for crop protection.

    Publication

    The calcium-permeable channel OSCA1.3 regulates plant stomatal immunity, Nature, 26 August 2020, DOI: 10.1038/s41586-020-2702-1

    https://www.nature.com/articles/s41586-020-2702-1

    Contact person

    Prof. Dr. Rainer Hedrich, Chair of Botany I (Plant Physiology and Biophysics), University of Würzburg, T +49 931 31-86100, hedrich@botanik.uni-wuerzburg.de

    By Robert Emmerich

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