Evolution of protein transport to the chloroplast envelope membranes

Day, Philip M; Theg, Steven M.

doi:10.1007/s11120-018-0540-x

Cited by 31 publications

(20 citation statements)

References 98 publications

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“…Our results showing that b-barrels use the TOC complex indicate that they are not directly inserted from the cytosol by an OEP80-containing complex. Instead, they favor the previously proposed model that predicts b-barrels traverse the OM before being inserted from the IMS side of the membrane (Lee et al, 2014;Richardson et al, 2014;Day and Theg, 2018). This model is comparable to b-barrel targeting to the mitochondrial OM where insertion by the Omp85 containing sorting and assembly machinery is coupled to import through the TOM machinery (Qiu et al, 2013).…”

Section: Discussionmentioning

confidence: 47%

Chloroplast Outer Membrane β-Barrel Proteins Use Components of the General Import Apparatus

2019

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Chloroplasts evolved from a cyanobacterial endosymbiont that resided within a eukaryotic cell. Due to their prokaryotic heritage, chloroplast outer membranes contain transmembrane b-barrel proteins. While most chloroplast proteins use N-terminal transit peptides to enter the chloroplasts through the translocons at the outer and inner chloroplast envelope membranes (TOC/TIC), only one b-barrel protein, Toc75, has been shown to use this pathway. The route other b-barrel proteins use has remained unresolved. Here we use in vitro pea (Pisum sativum) chloroplast import assays and transient expression in Nicotiana benthamiana to address this. We show that a paralog of Toc75, outer envelope protein 80 kD (OEP80), also uses a transit peptide but has a distinct envelope sorting signal. Our results additionally indicate that b-barrels that do not use transit peptides also enter the chloroplast using components of the general import pathway.

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Section: Discussionmentioning

confidence: 47%

Chloroplast Outer Membrane β-Barrel Proteins Use Components of the General Import Apparatus

2019

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“…The components of the Toc and Tic machinery share a mixed pro- and eukaryotic ancestry 89,90 . Toc75, the β-barrel import pore in the outer membrane, is of prokaryotic origin and a member of the Omp85 superfamily 25 .…”

Section: Discussionmentioning

confidence: 99%

Major changes in plastid protein import and the origin of the Chloroplastida

Knopp

Garg

Handrich

et al. 2019

Preprint

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10While core components of plastid protein import (Toc and Tic) and the principle of using N-11 terminal targeting sequences (NTS) are conserved, lineage-specific differences are known. 12Rhodophytes and glaucophytes carry a conserved NTS motif, which was lost in the green 13 lineage that also added novel proteins to Toc and Tic. Here we compare the components of 14 plastid protein import and generated RNA-Seq, pigment profile and trans-electron microscopy 15data based on high-light stress from representatives of the three archaeplastidal groups. In light 16 of plastid protein targeting, we compare the response to high-light stress of archaeplastidal 17representatives based on RNA-Seq, pigment profile and trans-electron microscopy data. Like 18 land plants, the chlorophyte Chlamydomonas reinhardtii displays a broad respond to high-light 19 stress, not observed to the same degree in the glaucophyte Cyanophora paradoxa or the 20 rhodophyte Porphyridium purpureum. We find that only the green lineage encodes a conserved 21 duplicate of the outer plastid membrane protein channel Oep80, namely Toc75 and suggest that 22 the ability to respond to high-light stress entailed evolutionary changes in protein import, 23including the departure from phenylalanine-based targeting and the introduction of a green-24 specific Toc75 next to other import components unique to Chloroplastida. One consequence of 25 relaxed NTS specificity was the origin of dual-targeting of plastid derived proteins to 26 mitochondria and vice versa, using a single ambiguous NTS. Changes in the plastid protein 27 import enabled the green lineage to import proteins at a more efficient rate, including those 28 required for high-light stress response, a prerequisite for the colonization of land. 29 30

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“…Once exposed to the stroma, the transit peptide is processed by the stromal processing peptidase, and the polypeptide folds and assembles with other polypeptides in the stroma or engages additional suborganellar targeting pathways to the thylakoid or inner envelope membranes [1,2]. A number of additional proteins that interact with the core machinery to facilitate import or suborganellar targeting are described in detail in other recent reviews [1,[3][4][5][6][7][8][9]. These components are not included here because they play accessory roles or are present only in select species and are therefore not considered core components of the general import machinery.…”

Section: The General Import Pathwaymentioning

confidence: 99%

“…The endosymbiotic evolution of chloroplasts from a cyanobacterial ancestor resulted in the transfer of the majority of genes from the bacterial endosymbiont to the host cell nucleus. As a consequence, plants evolved at least four distinct pathways to mediate the targeting of thousands of nuclear encoded proteins back to the organelle [1,2]. The vast majority of proteins are targeted via the interaction of their intrinsic targeting signals (transit peptides) with the general import machinery of chloroplasts, which consists of translocon complexes in the outer (TOC) and inner (TIC) envelope membranes ( Fig.…”

Section: Introductionmentioning

confidence: 99%

“…The vast majority of proteins are targeted via the interaction of their intrinsic targeting signals (transit peptides) with the general import machinery of chloroplasts, which consists of translocon complexes in the outer (TOC) and inner (TIC) envelope membranes ( Fig. 1) [1,[3][4][5][6][7][8][9]. TOC and TIC are physically linked to form supercomplexes that mediate direct transport of preproteins from the cytoplasm into the organelle interior [10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

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The TOC GTPase Receptors: Regulators of the Fidelity, Specificity and Substrate Profiles of the General Protein Import Machinery of Chloroplasts

Schnell

2019

Protein J

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More than 2500 nuclear encoded preproteins are required for the function of chloroplasts in terrestrial plants. These preproteins are imported into chloroplasts via the concerted action of two multi-subunit translocons of the outer (TOC) and inner (TIC) membranes of the chloroplast envelope. This general import machinery functions to recognize and import proteins with high fidelity and efficiency to ensure that organelle biogenesis is properly coordinated with developmental and physiological events. Two components of the TOC machinery, Toc34 and Toc159, act as the primary receptors for preproteins at the chloroplast surface. They interact with the intrinsic targeting signals (transit peptides) of preproteins to mediate the selectivity of targeting, and they contribute to the quality control of import by constituting a GTP-dependent checkpoint in the import reaction. The TOC receptor family has expanded to regulate the import of distinct classes of preproteins that are required for remodeling of organelle proteomes during plastid-type transitions that accompany developmental changes. As such, the TOC receptors function as central regulators of the fidelity, specificity and selectivity of the general import machinery, thereby contributing to the integration of protein import with plastid biogenesis. Keywords Chloroplast biogenesis • Chloroplast protein import • Protein targeting • Protein quality control • Transit peptide • Endosymbiosis Abbreviations TOC Translocon at the outer chloroplast envelope TIC Translocon at the inner chloroplast envelope Hsp Heat shock protein POTRA Polypeptide transport associated SP Suppressor of ppi1 UPS Ubiquitin proteasome system Cdc48 Cell cycle division 48 ERAD ER-associated degradation GA Gibberellic acid KOC Kinase of the outer chloroplast membrane Ppi Plastid protein import mutant CHIP Carboxyl-terminus of Hsp70-interacting protein

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Evolution of protein transport to the chloroplast envelope membranes

Cited by 31 publications

References 98 publications

Chloroplast Outer Membrane β-Barrel Proteins Use Components of the General Import Apparatus

Chloroplast Outer Membrane β-Barrel Proteins Use Components of the General Import Apparatus

Major changes in plastid protein import and the origin of the Chloroplastida

The TOC GTPase Receptors: Regulators of the Fidelity, Specificity and Substrate Profiles of the General Protein Import Machinery of Chloroplasts

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