{
  "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.",
  "abstract_shown": true,
  "affiliations": [
    "University of Oxford"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 6,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "P. Zhang"
    },
    {
      "name": "Z. Hou"
    },
    {
      "name": "Y. Shen"
    },
    {
      "affs": [
        0
      ],
      "name": "Z. Zhang"
    },
    {
      "name": "P. Lu"
    },
    {
      "name": "A. Katzourakis"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/57rjfdb8kbys6.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.08.28.747797",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.08.28.747797v1.full",
  "id": "57rjfdb8kbys6",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.08.28.747797v1",
  "language": null,
  "licence": "CC-BY-ND",
  "licence_label": "CC BY-ND",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by-nd/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "biorxiv",
      "plant biology"
    ],
    [
      "openalex",
      "1312|RNA and protein synthesis mechanisms"
    ]
  ],
  "openalex": "W7207872254",
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.08.28.747797v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-08-28",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/57rjfdb8kbys6.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:50Z",
      "native_id": "10.64898/2026.08.28.747797",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.08.28.747797v1"
    }
  ],
  "subjects": [
    {
      "field": "biology",
      "origin": "biorxiv:plant biology",
      "subfield": "plant-biology"
    }
  ],
  "title": "In-cell structural analysis reveals a distinctive chloroplast ribosome in Chlamydomonas reinhardtii",
  "title_text": "In-cell structural analysis reveals a distinctive chloroplast ribosome in Chlamydomonas reinhardtii",
  "type": "preprint",
  "updated_at": "2026-10-30T12:18:50Z",
  "url": "https://research.draconitic.com/paper/57rjfdb8kbys6",
  "venue": "bioRxiv",
  "versions": []
}