In-cell structural analysis reveals a distinctive chloroplast ribosome in Chlamydomonas reinhardtii
- 1University of Oxford
Abstract
Chloroplast ribosomes synthesize plastid-encoded components of photosynthetic machinery, yet their structure and organization remain poorly understood. We combined cryo-focused ion beam milling, cryo-electron tomography and subtomogram averaging to determine native chloroplast ribosomes in Chlamydomonas reinhardtii. The 4.4-4.9 [A] structure revealed a large arch-like extension on the small subunit (SSU). Comparisons with bacterial and plant chloroplast ribosomes, supported by proteomics, AlphaFold3 predictions and a recent atomic model, indicate that the arch is formed by insertions and extensions in SSU proteins. Classification resolved active, thylakoid-associated ribosomes with density adjacent to the nascent peptide exit and an arch-moved state enriched among thylakoid-associated particles, with coordinated displacement of the arch and beak. Phylogenetic analysis revealed an evolutionary mosaic: the uS3c insertion is broadly distributed across Chlorophyceae, whereas the uS2c insertion, uS5c and PSRP7 are concentrated in Chlamydomonadales, with PSRP7 also in Sphaeropleales. Nuclear-encoded components were recruited stepwise onto a plastid-encoded scaffold, with all four under comparable purifying selection. These findings link a lineage-specific SSU extension to ribosome dynamics, thylakoid association and evolution, highlighting the value of in-cell structural analysis.
Related
- All in this together: Multifactorial stress combination promotes cell aggregation in Chlamydomonas reinhardtii
- Conserved inhibitory mechanisms of root-associated bacteria towardsArabidopsis thaliana and Chlamydomonas reinhardtii
- PRK introns provide modular tools for enhanced transgene expression in Chlamydomonas reinhardtii
- Two genomes in one mitochondrion: mitochondrial heteroplasmy and mitogenome dynamics in Chlamydomonas reinhardtii
- Intracellular distribution and speciation of indium in the green microalgae Chlamydomonas reinhardtii
BibTeX
@misc{zhang2026incell,
title = {{In-cell structural analysis reveals a distinctive chloroplast ribosome in Chlamydomonas reinhardtii}},
author = {P. Zhang and Z. Hou and Y. Shen and Z. Zhang and P. Lu and A. Katzourakis},
howpublished = {bioRxiv},
year = {2026},
month = aug,
doi = {10.64898/2026.08.28.747797},
url = {https://www.biorxiv.org/content/10.64898/2026.08.28.747797v1},
note = {CC BY-ND},
}
RIS
TY - UNPB
TI - In-cell structural analysis reveals a distinctive chloroplast ribosome in Chlamydomonas reinhardtii
AU - P. Zhang
AU - Z. Hou
AU - Y. Shen
AU - Z. Zhang
AU - P. Lu
AU - A. Katzourakis
PY - 2026
DA - 2026/08/28
PB - bioRxiv
DO - 10.64898/2026.08.28.747797
UR - https://www.biorxiv.org/content/10.64898/2026.08.28.747797v1
AB - Chloroplast ribosomes synthesize plastid-encoded components of photosynthetic machinery, yet their structure and organization remain poorly understood. We combined cryo-focused ion beam milling, cryo-electron tomography and subtomogram averaging to determine native chloroplast ribosomes in Chlamydomonas reinhardtii. The 4.4-4.9 [A] structure revealed a large arch-like extension on the small subunit (SSU). Comparisons with bacterial and plant chloroplast ribosomes, supported by proteomics, AlphaFold3 predictions and a recent atomic model, indicate that the arch is formed by insertions and extensions in SSU proteins. Classification resolved active, thylakoid-associated ribosomes with density adjacent to the nascent peptide exit and an arch-moved state enriched among thylakoid-associated particles, with coordinated displacement of the arch and beak. Phylogenetic analysis revealed an evolutionary mosaic: the uS3c insertion is broadly distributed across Chlorophyceae, whereas the uS2c insertion, uS5c and PSRP7 are concentrated in Chlamydomonadales, with PSRP7 also in Sphaeropleales. Nuclear-encoded components were recruited stepwise onto a plastid-encoded scaffold, with all four under comparable purifying selection. These findings link a lineage-specific SSU extension to ribosome dynamics, thylakoid association and evolution, highlighting the value of in-cell structural analysis.
ER -