Long and complex molecules of DNA are precisely organized within cells to support genome maintenance and gene expression. A unique and poorly understood form of DNA organization exists in chloroplasts, which are organelles responsible for photosynthesis in plants and algal cells. Chloroplast genomes, together with associated proteins, form membrane-less structures known as nucleoids. The internal arrangement of the nucleoid, molecular mechanisms of DNA organization, and connections between nucleoid structure and gene expression remain mostly unknown.
In a new paper in Proceedings of the Natural Academy of Sciences (PNAS), the Wierzbicki group shows that chloroplast DNA is organized by binding to membranes present inside the organelle. "We propose that transcription, the initial step in the process of gene expression, plays an important role in organizing the chloroplast nucleoid into a transcriptionally active membrane-associated core and a less active periphery," they suggest.
They explain: "Arabidopsis thaliana chloroplast nucleoids have a unique sequence-specific organization driven by DNA binding to the thylakoid membranes. DNA associated with the membranes has high protein occupancy, has reduced DNA accessibility, and is highly transcribed. In contrast, genes with low levels of transcription are further away from the membranes, have lower protein occupancy, and have higher DNA accessibility. Membrane association of active genes relies on the pattern of transcription and proper chloroplast development. We propose a speculative model that transcription organizes the chloroplast nucleoid into a transcriptionally active membrane-associated core and a less active periphery."
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The Study: Membrane association of active genes organizes the chloroplast nucleoid structure
Miguel Palomar, Yoonjin Cho, Sho Fujii, M. Hafiz Rothi, Sarah Jaksich, Ji-Hee Min, Adriana N. Schlachter, Joyful Wang, Zhengde Liu, and Andrzej T. Wierzbicki
July 5, 2024121 (28) e2309244121
