Project description:Chloroplast biogenesis represents a crucial step in seedling development, and is essential for the transition to autotrophic growth in plants. This light-controlled process relies on the transcription of nuclear and plastid genomes that drives the effective assembly and regulation of the photosynthetic machinery. Here we reveal a novel regulation level for this process by showing the involvement of chromatin remodelling in the coordination of nuclear and plastid gene expression for proper chloroplast biogenesis and function. The two Arabidopsis homologs of the yeast EPL1 proteins, core components of the NuA4 histone acetyl-transferase complex, are essential for the correct assembly and performance of chloroplasts. EPL1 proteins are necessary for the coordinated expression of nuclear genes encoding most of the components of chloroplast transcriptional machinery, specifically promoting H4K5Ac deposition in these loci. These data unveil a key participation of epigenetic regulatory mechanisms in the coordinated expression of the nuclear and plastid genomes.
Project description:Gene expression in plastids of higher plants is dependent on two different transcription machineries, a plastid-encoded bacterial-type RNA polymerase (PEP) and a nuclear-encoded phage-type RNA polymerase (NEP), which recognize distinct types of promoters. The division of labor between PEP and NEP during plastid development and in mature chloroplasts is unclear due to a lack of comprehensive information on promoter usage. Here we present a thorough investigation into the distribution of PEP and NEP promoters within the plastid genome of barley (Hordeum vulgare L). Using a novel differential RNA sequencing approach, which discriminates between primary and processed transcripts, we obtained a genome-wide map of transcription start sites in plastids of mature first leaves. PEP-lacking plastids of the albostrians mutant allowed for the unambiguous identifications of NEP promoters. We observed that the chloroplast genome contains many more promoters than genes. According to our data, most genes (including genes coding for photosynthesis proteins) have both PEP and NEP promoters. We also detected numerous transcription start sites within operons indicating transcriptional uncoupling of genes in polycistronic gene clusters. Moreover, we mapped many transcription start sites in intergenic regions, as well as opposite to annotated genes demonstrating the existence of numerous non-coding RNA candidates.