Molecular characterization of a new protein complex in plants essential for heterochromatin silencing and genome stability.

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Plants develop through the activity of meristems, which contain pools of self-renewing stem cells that continuously provide new cells for the formation of all tissues and organs. Maintenance of these stem cell populations is essential for successful plant growth and development. Our published work has shown that two genes, which share a conserved transposon-related domain, play a crucial role in the maintenance of the root apical meristem. We named these genes MAINTENANCE of MERISTEM (MAIN) and MAINTENANCE of MERISTEMS LIKE 1 (MAIL1). Loss-of-function mutants for either gene show primary root growth arrest due to accumulation of DNA damage and cell death of stem cells. Moreover, these mutants show release of silencing of a subset of transposable element encoded genes in all tissues, which occurs by a so far unknown mechanism. Our preliminary results indicate that these proteins might be involved in an RNA processing complex. In this project we are aiming at the identification of the molecular function of these proteins by focusing on two complimentary approaches: We will perform Co-Immunoprecipitation experiments followed by mass spectrometry in order to identify the protein complex, in which these proteins act. Second, we will perform a suppressor screen aimed at the identification of the regulatory network that leads to the root growth arrest. Our results will reveal a so far unknown silencing mechanism in plants, which is probably based on RNA processing events. Moreover, we will provide fundamental new insight into the mechanisms that enable plants to maintain genome stability in meristems and to support root growth and re-establishment of stem cell function after DNA damage.