Dissection of the tetrapyrrole-mediated signaling pathway: Identification of components involved in signal transduction and of target genes

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Control of the essential tetrapyrrole biosynthesis requires retrograde signaling. Combinatorial analyses of global transcript profiles and identification of interaction partners of enzymes in the chlorophyll-synthesizing branch revealed that (I) chemically induced deregulation of expression of tetrapyrrole biosynthesis genes is a straight forward strategy to identify early up- and downregulated genes, (II) deregulated expression of enzymes rather than accumulation of specific Mg porphyrins affects nuclear gene expression, and (III) identified interaction partners likely contribute to the combination of different retrograde signals generated in plastids. The project aims to substantiate the mechanisms of tetrapyrrole pathway-mediated signaling. After evaluation of microarray and bioinformatics analyses target genes are identified and new components of the signaling pathway are proposed. Their contribution to retrograde signaling will be analyzed in transgenic lines by RNAi inactivation and overexpression. In parallel, a robust comparative analysis of the impact of tetrapyrrolic metabolites and effectors will be performed with photoautotrophic Arabidopsis cell cultures. Refined analyses of protein complexes for enzymes of the chlorophyll synthesis branch will be continued using transformants expressing tagged-proteins to reveal their contribution to control and signaling of the tetrapyrrole biosynthetic pathway. New insights are expected allowing a substantial assessment how tetrapyrrole metabolism is integrated in plastid-derived retrograde signaling.