Nuclear calcium regulation of plant development

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Calcium signalling is essential for growth and development, in both plants and animals. In animals nuclear calcium release is a potent regulator of neuronal gene expression and of cell proliferation. Nuclear calcium signalling is also known to be essential in legumes to promote associations with nitrogen fixing bacteria and phosphate delivering arbuscular mycorrhizal fungi. Legumes are among the world's most important agricultural food crops that are beneficial to billions of farmers and consumers worldwide and provide an essential aspect of natural soil enrichment of organic nitrogen compounds. The mechanisms of plant nuclear calcium signalling were poorly understood. During my work I have used the symbiotic associations in legumes as a platform to dissect plant nuclear calcium signalling. Using a wide range of approaches, I discovered a number of ion channels located at the nuclear envelope that are responsible for symbiotic nuclear calcium release. Among them, I defined the first plant nuclear-associated calcium channels encoded by cyclic nucleotide gated channels (CNGC15s). The CNCG15s sit at the nuclear envelope in a complex with a potassium permeable channel (DMI1), also required for the generation of the symbiotic nuclear calcium signals. Interestingly, CNGC15s and DMI1 are conserved across all land plants, including non-symbiotic species, strongly suggesting that they have other functions during plant development. Consistent with this I have found a number of defects in Arabidopsis lines mutated in CNGC15 and DMI1, that include root developmental defects. I propose that my research in legumes has revealed the generic plant machinery involved in the regulation of nuclear calcium release. By studying the components that regulate nuclear calcium release I will be able to understand when and where nuclear calcium signalling is important. My proposal will focus on the role of nuclear calcium signalling during root development, both root growth and associations with symbiotic microorganisms. Consistent with a function for CNGC15 and DMI1 in root development I have observed nuclear calcium responses in Arabidopsis root meristematic cells during their response to the phytohormones auxin and cytokinin. These calcium responses are mechanistically different from the nuclear calcium signals observed in legumes during symbiotic associations. My proposed research integrates molecular biology, genetics, cell biology, chemistry, electrophysiology and mathematical modelling to investigate how CNGC15-DMI1 regulates nuclear calcium release leading to plant developmental processes. It will use a large collection of Arabidopsis mutant and transgenic lines, that I have already generated, with a panel of nuclear calcium sensors allowing detection of nuclear calcium signals in an array of Arabidopsis mutants. My work will dissect the functions that nuclear calcium signalling plays in root developmental processes and how diverse nuclear calcium signals are encoded. Finally, through a combination of transcriptomics and mutant screens, I will be uniquely poised to decipher the downstream signalling components associated with nuclear calcium signalling during root development.