Cytokinin as a regulator of chloroplast development and function

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A role of the plant hormone cytokinin in regulating the development and activity of chloroplasts was described soon after its discovery more than fifty years ago. However, the molecular mechanisms underlying this activity remain elusive despite great progress in understanding the metabolism and cellular signalling of the hormone. This research proposal capitalizes on the availability of numerous novel cytokinin mutants and transgenic lines enabling new approaches to decipher cytokinin activities on plastids. In a first part, a detailed study of the consequences of cytokinin deficiency on plastid development and function will be performed in Arabidopsis thaliana. This will be accompanied by a study on the relevance of the plastids' own cytokinin metabolism using mutants of plastid-located cyto-kinin synthesizing enzymes, as well as enhanced plastid-specific cytokinin degradation. A significant activity of cytokinin on plastid development is a more rapid greening in light, which will form the basis to describe the role of cytokinin in plastid development, as well as to search for mutants of this activity. A hitherto unknown function of cytokinin, its protective function during light stress, will be studied in a third part of the project. Numerous stress-related parameters including production of reactive oxygen species, the scavenging system, lipid peroxidation and the D1 repair cycle will be analyzed in cytokinin mutants. A genetic approach is chosen to identify functionally relevant genes of this pathway.