Genetic Dissection of Organellar-Gene-Expression (OGE)-Dependent Retrograde Signaling in Arabidopsis

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Most plastid proteins are nucleus-encoded and their transcriptional regulation involves retrograde signaling. Impairment of organellar gene expression (OGE) by chemicals such as lincomycin, or mutations such as prpl11 or prors1, trigger a retrograde signaling pathway and result in transcriptional down-regulation of nuclear photosynthetic genes. Work on the Arabidopsis prors1 mutant showed that when OGE is perturbed, signals derived from both chloroplasts and mitochondria cooperate in down regulating nuclear photosynthetic gene expression. In the previous funding period we have generated lines with repressible OGE, discovered that the gun1 mutation overrides OGE signaling triggered by prors1, and identified the first rls (relaxed LHCB repression) mutants with derepressed LHCB expression in the prors1 background. In the next funding period we will identify target genes of OGE and GUN1 signaling starting from transcriptome kinetics of lines with repressible OGE or GUN1 activity. We will classify and characterize the rls mutants and identify at least two RLS genes. Thirdly, we will characterize in detail the role of GUN1 in OGE signaling, considering the possibility that GUN1 functionally interacts with plastid ribosomes. This combined strategy will enable us to identify factors involved in chloroplast or mitochondrial signaling, as well as factors that integrate the activities of the two signaling pathways.