How chromatin contributes to make plants green: Unveiled a NuA4-mediated histone acetylation mechanism regulating Arabidopsis chloroplast biogenesis

Photomorphogenic changes encompass a wide range of responses including the differentiation of non-photosynthetic plastids into chloroplasts, a crucial step in the transition from heterotrophic to autotrophic growth in plants. This process is light-induced and relies on the orchestrated transcription of nuclear and plastid genes, enabling the effective assembly and regulation of the photosynthetic machinery. In this work, we reveal a novel regulation level for this process by showing the involvement of chromatin remodelling in the nuclear control of plastid gene expression for proper chloroplast biogenesis and function. The two Arabidopsis homologs of yeast EPL1 protein, components of the NuA4 histone acetyltransferase complex, are essential for plastid transcription and correct chloroplast development and performance. We show that EPL1 proteins are light-regulated and necessary for concerted expression of nuclear genes encoding most components of chloroplast transcriptional machinery, directly mediating H4K5ac deposition at these loci and promoting the expression of plastid genes required for chloroplast biogenesis. These data unveil a NuA4-mediated mechanism regulating chloroplast biogenesis that links the transcription of nuclear and plastid genomes during chloroplast development.