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Interaktion zwischen dem circadianen System und pflanzlichen Immunantworten bei Arabidopsis thaliana

Fachliche Zuordnung Organismische Interaktionen, chemische Ökologie und Mikrobiome pflanzlicher Systeme
Förderung Förderung von 2008 bis 2012
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 71247354
 
Erstellungsjahr 2014

Zusammenfassung der Projektergebnisse

The project focused on the interconnection between two key regulatory systems in plants: The circadian clock system serves to optimally align plant physiology to the periodic changes of light and darkness in the environment and by these means contributes to fitness of the plant. The innate immune system provides strategies for the plant to combat invading pathogens. In particular we have focussed on the impact of the circadian clock on plant immune responses, using the pathogen associated molecular pattern flg22 and the well established interaction between Pseudomonas syringae and Arabidopsis thaliana as a model. We have shown that in Arabidopsis thaliana the magnitude of a series of immune responses elicited by the pathogen-associated molecular pattern flg22, by virulent and by avirulent Pseudomonas syringae strains depend on the time-of-day of inoculation. Specifically, we have shown for the first time that the oxidative burst is stronger when flg22 is infiltrated in the morning in wild type plants, but not in the arrhythmic phytoclock1 mutant and thus is controlled by the clock. Furthermore, we have shown for the first time that the cell death associates with the hypersensitive response is under clock control. Similarly, when bacteria are syringe-infiltrated into the leaf, defense gene induction is higher and bacterial growth is suppressed more strongly upon morning inoculation in wild type but not in pcl1 plants. These results were similar to those reported by Bhardwaj and colleagues (Bhardwaj et al. 2011) but contrasted with results reported by Shin and colleagues (Shin et al. 2012) that found stronger suppression of bacterial growth upon infection in the evening. By systematically investigating this we found that the clock effect depends on the mode of infection: Upon spray-inoculation onto the leaf surface, defense gene induction is higher and bacterial growth is suppressed more strongly upon evening inoculation. Furthermore, we have found that this different phasing of pre-invasive and post-invasive defense by the circadian clock relates to clock-regulated stomatal movement. In particular, we show that the clock component TIME OF COFFEE may impact pathogen defense via clock-regulated stomatal movement apart from its known role in time-of-day-dependent jasmonate responses. Furthermore, in collaboration with Prof. James R. Alfano we have investigated the role of the circadian clock regulated RNA-binding protein in plant immunity. Plants overexpressing At-GRP7 display enhanced immune reactions. Specifically, flg22-triggered oxidative burst and callose deposition are enhanced in independent AtGRP7-ox plants. Furthermore, the growth of virulent Pst DC3000 bacteria is suppressed more strongly in AtGRP7-ox plants than in wt plants. Moreover, AtGRP7-ox plants show a stronger hypersensitive response (HR) in response to avirulent Pst avrRpt2. The immunity phenotypes depend on the presence of a conserved arginine residue within the RNA-binding domain. In line with this, we have shown that AtGRP7 binds to defence-related genes in vivo.

Projektbezogene Publikationen (Auswahl)

 
 

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