Circadian regulation of plant immunity calcium signalling

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In order to survive, plants and crops have to respond rapidly, and appropriately, to the multitude of different environmental stimuli they face. Key to this is the ability to discriminate between different stimuli e.g. pathogen attack versus drought stress. An increase in cellular calcium concentration acts as a trigger in plant cells to activate the appropriate response: expressing the correct proteins to defend against a specific stress. Different stimuli provoke calcium increases with different and unique properties, known as "calcium signatures" which encode the appropriate response. We have previously shown that calcium regulates at least four different transcription factor families (Whalley et al., 2011), that different calcium signatures activate different sets of genes (Whalley and Knight, 2013), and we have identified mechanisms by which these calcium signatures are "decoded" (Liu et al., 2015; Lenzoni et al., 2018). Importantly, the appropriate response to a given stress needs to be different at different times of day to maximise fitness. We have most recently found that for pathogen stress the specific nature of pathogen-mediated calcium signature depends on the subjective time-of-day i.e. the calcium signatures, and subsequent pathogen-induced gene expression and tolerance, are modified by the circadian clock. This form of regulation of signalling pathways by circadian clocks is called "gating" and is vital for fitness and survival, yet very little in known about the mechanism or components involved. An understanding of this process would allow the breeding/engineering of crops with improved fitness in a changing climate.Aims:To answer the following biological questions:(i) How are calcium signatures controlled by the circadian clock? What are the clock components involved in this gating phenomenon?(ii) Which downstream proteins are involved in decoding these novel calcium signatures, modified by the circadian clock?(iii) Which transcription factors are involved in recognising these novel calcium signatures?(iv) What is the mechanism by which these novel calcium signatures are converted into the appropriate response?