Final Activity Report Summary - CDPKSIGNALING (Involvement of CDPK in environmental stress signaling) The research project refers to the crucial agronomic question of plant survival in adverse environmental conditions. The scientific objective was to elucidate molecular mechanisms underlying early events in environmental stress signalling mediated by calcium-dependent protein kinases (CDPKs). These kinases are scarcely studied in Europe although they represent a novel class of calcium sensors, with both calcium binding and phosphorylation activity properties. As a result, CDPKs get activated when they bind calcium, whose concentration increases in response to multiple environmental and developmental cues.An integrative approach including genomics, genetics, cell biology and biochemistry, has been implemented and combined with bioinformatics to decipher calcium signalling mediated by CDPKs in response to cold and to the bacterial elicitor flg22. Using a functional genomic screen and genome-wide gene expression profiling, we showed that a specific subset of CDPKs can mimic flg22 induction of gene expression. We also identified interplay between MAPK and CDPK in early gene reprogramming, highlighting a complex signalling network. Remarkably, CDPK mutants were impaired in flg22 responses including production of reactive oxygen species and gene expression, correlated with enhanced susceptibility to a bacterial pathogen. Thus, we demonstrated that CDPKs play a crucial role in calcium-mediated plant innate immunity. Interestingly, a larger subset of CDPKs could mimic cold induction of gene expression, suggesting that different stimuli induce distinct calcium signals that are recognised by different CDPKs. We identified a specific transcription factor involved in cold signalling as a CDPK substrate in vitro. Importantly, we showed that this transcription factor could be activated by CDPKs in vivo. Taken together, the results of this project demonstrated that CDPKs are key regulators in plant responses to environmental stresses, either in biotic or abiotic conditions.
