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Plant Cell. 2019 Oct 7. pii: tpc.00263.2019. doi: 10.1105/tpc.19.00263. [Epub ahead of print]

Photosystem Biogenesis Is Localized to the Translation Zone in the Chloroplast of Chlamydomonas.

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Concordia University CITY: Montreal STATE: Quebec Canada [CA].
McGill University CITY: Montreal STATE: Quebec POSTAL_CODE: H3A 0C7 Canada [CA].
Concordia University CITY: Montreal STATE: Quebec POSTAL_CODE: H4B 1R6 Canada [CA]


Intracellular processes can be localized for efficiency or regulation. For example, localized mRNA translation by chloroplastic ribosomes occurs in the biogenesis of photosystem II, one of the two photosystems of the photosynthetic electron transport chain in the chloroplasts of plants and algae. The biogenesis of both photosystems, I and II, requires the synthesis and assembly of their constituent polypeptide subunits, pigments, and cofactors. Although these biosynthetic pathways are well characterized, less is known about when and where they occur in developing chloroplasts. We used fluorescence microscopy in the unicellular alga Chlamydomonas reinhardtii to reveal spatiotemporal organization in photosystem biogenesis. We focused on translation by chloroplastic ribosomes and chlorophyll biosynthesis in two developmental contexts of active photosystem biogenesis: 1) growth of the mature chloroplast and 2) greening of a non-photosynthetic chloroplast. The results reveal that a translation zone is the primary location of the biogenesis of photosystems I and II. This discretely localized region within the chloroplast contrasts with the distributions of photosystems throughout this organelle and, therefore, is likely a hub where anabolic pathways converge for photosystem biogenesis.


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