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Assembly of two functionally-distinct protein import complexes in the outer membrane of plant chloroplasts (interactome data)

ABSTRACT: The TOC protein translocon delivers thousands of nucleus-encoded proteins to chloroplasts and to related non-photosynthetic plastids. It comprises the β-barrel channel, Toc75, and multiple isoforms of receptor GTPases, Toc33 and Toc159. However, exactly how TOC complexes are assembled in different plastid types, is not known. Here, we present detailed characterization of two distinct TOC complexes, TOC-P and TOC-N, from photosynthetic chloroplasts and non-photosynthetic plastids, respectively. The assembled complexes are distinguished by having different sets of receptors, but both possess Toc75 which we identify as a central hub in TOC biogenesis: assembly is driven by TOC75 expression, with the Toc33and Toc159 GTPases being added sequentially thereafter. Integrative structural analysis revealed a modular architecture for TOC-P comprising a cytosolic GTPase receptor module linked flexibly to a membrane β-barrel channel module. TOC-N has a similar overall architecture, albeit with some clear differences that likely account for observed functional differences related to client specificity.

INSTRUMENT(S):

ORGANISM(S): Arabidopsis Thaliana (mouse-ear Cress)

SUBMITTER: Vaishnavi Ravikumar

LAB HEAD: Dr Marjorie

PROVIDER: PXD072672 | Pride | 2026-03-22

REPOSITORIES: Pride

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			Action	DRS
	QEX02_MF_211220_MF_SN2-test_122.raw	Raw
	QEX02_MF_211220_MF_SN7-test_124.raw	Raw
	QEX03_MF_220106_SN10_test_035.raw	Raw
	QEX03_MF_220106_SN11_test_039.raw	Raw
	QEX03_MF_220106_SN12_test_041.raw	Raw

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Assembly of two functionally-distinct protein import complexes in the outer membrane of plant chloroplasts (crosslinking data)

Project description:The TOC protein translocon delivers thousands of nucleus-encoded proteins to chloroplasts and to related non-photosynthetic plastids. It comprises the β-barrel channel, Toc75, and multiple isoforms of receptor GTPases, Toc33 and Toc159. However, exactly how TOC complexes are assembled in different plastid types, is not known. Here, we present detailed characterization of two distinct TOC complexes, TOC-P and TOC-N, from photosynthetic chloroplasts and non-photosynthetic plastids, respectively. The assembled complexes are distinguished by having different sets of receptors, but both possess Toc75 which we identify as a central hub in TOC biogenesis: assembly is driven by TOC75 expression, with the Toc33and Toc159 GTPases being added sequentially thereafter. Integrative structural analysis revealed a modular architecture for TOC-P comprising a cytosolic GTPase receptor module linked flexibly to a membrane β-barrel channel module. TOC-N has a similar overall architecture, albeit with some clear differences that likely account for observed functional differences related to client specificity.

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Project description:Plastids are endosymbiotic organelles containing their own genomes, which are transcribed by two types of RNA polymerases. One of those enzymes is a bacterial-type, multi-subunit polymerase encoded by the plastid genome. The plastid-encoded polymerase (PEP) is required for efficient expression of genes encoding proteins involved in photosynthesis. Despite the importance of PEP, its DNA binding locations have not been studied on the genome-wide scale at high resolution. We established a highly specific approach to detect the genome-wide pattern of PEP binding to chloroplasts DNA using ptChIP-seq. We found that in mature Arabidopsis thaliana chloroplasts, PEP has a complex pattern of binding to DNA with preferential association at genes encoding rRNA, tRNA and a subset of photosynthetic proteins. Sigma factors SIG2 and SIG6 strongly impact PEP binding to a subset of tRNA genes and have more moderate effects on PEP binding throughout the rest of the genome. PEP binding is commonly enriched on gene promoters, around transcription start sites. Finally, the levels of PEP binding to DNA are correlated with the levels of RNA accumulation, which allowed estimating the quantitative contribution of transcription to RNA accumulation.

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The chloroplast outer and inner envelope membrane translocase (TOC/TIC) interaction network identifies a 23 kDa glycine-rich protein as new subunit of the 1-MDa TIC complex

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