Plastid translation and plant development

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By using a combination of transplastomic and pharmacological approaches, work in the current funding period has established novel tools for studying the retrograde signals generated from plastid translation. Genetic and pharmacological studies have indicated that plastid genome-encoded protein(s) serve as generator of the retrograde signal that determines leaf shape in response to plastid translational activity. Mutant analyses have revealed that the retrograde signal is xanthoxin, a precursor of the phytohormone abscisic acid (ABA), and have suggested a molecular mechanism for how the translational activity of the chloroplast is converted into the metabolic signal that triggers the phenotypic responses. Future research aims to rigorously test our current working model using biochemical and genetic approaches. These will comprise comparative analyses of available ABA mutants, plastid translation mutants and transplastomic lines as well as overexpression and RNAi-mediated downregulation of candidate components in the signal transduction chain. Furthermore, the (de)regulation of nuclear genes in response to the signal will be analyzed with transcript and metabolite profiling techniques to (i) reveal new nuclear target genes that are controlled by this retrograde pathway and (ii) identify additional signalling components.