scholarly journals Major Changes in Plastid Protein Import and the Origin of the Chloroplastida

iScience ◽  
2020 ◽  
Vol 23 (3) ◽  
pp. 100896 ◽  
Author(s):  
Michael Knopp ◽  
Sriram G. Garg ◽  
Maria Handrich ◽  
Sven B. Gould
Keyword(s):  
Protein Import ◽  
Plastid Protein

scholarly journals Retrograde signalling in a virescent mutant triggers an anterograde delay of chloroplast biogenesis that requires GUN1 and is essential for survival

2020 ◽  
Vol 375 (1801) ◽  
pp. 20190400 ◽  
Author(s):  
Naresh Loudya ◽  
Tolulope Okunola ◽  
Jia He ◽  
Paul Jarvis ◽  
Enrique López-Juez
Keyword(s):  
Protein Import ◽  
Early Stage ◽  
Plastid Development ◽  
Plastid Genomes ◽  
Expression Of Genes ◽  
Fitness Value ◽  
Retrograde Signalling ◽  
Value Loss ◽  
Elevated Expression ◽  
Plastid Protein

Defects in chloroplast development are ‘retrograde-signalled’ to the nucleus, reducing synthesis of photosynthetic or related proteins. The Arabidopsis cue8 mutant manifests virescence, a slow-greening phenotype, and is defective at an early stage in plastid development. Greening cotyledons or early leaf cells of cue8 exhibit immature chloroplasts which fail to fill the available cellular space. Such chloroplasts show reduced expression of genes of photosynthetic function, dependent on the plastid-encoded polymerase (PEP), while the expression of genes of housekeeping function driven by the nucleus-encoded polymerase (NEP) is elevated, a phenotype shared with mutants in plastid genetic functions. We attribute this phenotype to reduced expression of specific PEP-controlling sigma factors, elevated expression of RPOT (NEP) genes and maintained replication of plastid genomes (resulting in densely coalesced nucleoids in the mutant), i.e. it is due to an anterograde nucleus-to-chloroplast correction, analogous to retention of a juvenile plastid state. Mutants in plastid protein import components, particularly those involved in housekeeping protein import, also show this ‘retro-anterograde’ correction. Loss of CUE8 also causes changes in mRNA editing. The overall response has strong fitness value: loss of GUN1, an integrator of retrograde signalling, abolishes elements of it (albeit not others, including editing changes), causing bleaching and eventual seedling lethality upon cue8 gun1 . This highlights the adaptive significance of virescence and retrograde signalling. This article is part of the theme issue ‘Retrograde signalling from endosymbiotic organelles’.

scholarly journals The novel chloroplast outer membrane kinase KOC1 is a required component of the plastid protein import machinery

2017 ◽  
Vol 292 (17) ◽  
pp. 6952-6964 ◽  
Author(s):  
Mónica Zufferey ◽  
Cyrille Montandon ◽  
Véronique Douet ◽  
Emilie Demarsy ◽  
Birgit Agne ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Protein Import ◽  
The Novel ◽  
Plastid Protein

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

2019 ◽  
Author(s):  
Michael Knopp ◽  
Sriram G. Garg ◽  
Maria Handrich ◽  
Sven B. Gould
Keyword(s):  
Protein Import ◽  
Light Stress ◽  
High Light ◽  
Rna Seq ◽  
High Light Stress ◽  
Dual Targeting ◽  
Plastid Protein ◽  
Pigment Profile ◽  
Microscopy Data ◽  
Green Lineage

AbstractWhile core components of plastid protein import (Toc and Tic) and the principle of using N-terminal targeting sequences (NTS) are conserved, lineage-specific differences are known. Rhodophytes and glaucophytes carry a conserved NTS motif, which was lost in the green lineage that also added novel proteins to Toc and Tic. Here we compare the components of plastid protein import and generated RNA-Seq, pigment profile and trans-electron microscopy data based on high-light stress from representatives of the three archaeplastidal groups. In light of plastid protein targeting, we compare the response to high-light stress of archaeplastidal representatives based on RNA-Seq, pigment profile and trans-electron microscopy data. Like land plants, the chlorophyte Chlamydomonas reinhardtii displays a broad respond to high-light stress, not observed to the same degree in the glaucophyte Cyanophora paradoxa or the rhodophyte Porphyridium purpureum. We find that only the green lineage encodes a conserved duplicate of the outer plastid membrane protein channel Oep80, namely Toc75 and suggest that the ability to respond to high-light stress entailed evolutionary changes in protein import, including the departure from phenylalanine-based targeting and the introduction of a green-specific Toc75 next to other import components unique to Chloroplastida. One consequence of relaxed NTS specificity was the origin of dual-targeting of plastid derived proteins to mitochondria and vice versa, using a single ambiguous NTS. Changes in the plastid protein import enabled the green lineage to import proteins at a more efficient rate, including those required for high-light stress response, a prerequisite for the colonization of land.High-lightsLoss of Phe-based N-terminal targeting sequences (NTS) triggered the origin of dual-targeting using a single ambiguous NTSThe Chloroplastida evolved a green-specific Toc75 for high throughput import, next to a universal and ancient Omp85 present in all ArchaeplastidaA broad response to high-light stress appears unique to ChloroplastidaRelaxation of functional constraints allowed a broader modification of the green Toc/Tic machineryCritical changes in plastid targeting enabled the origin and success of the Chloroplastida and their later conquer of land

Structural components involved in plastid protein import

2018 ◽  
Vol 62 (1) ◽  
pp. 65-75 ◽  
Author(s):  
Serena Schwenkert ◽  
Sophie Dittmer ◽  
Jürgen Soll
Keyword(s):  
Protein Import ◽  
Protein Complexes ◽  
Chloroplast Envelope ◽  
Structural Level ◽  
Conformational Switching ◽  
Chloroplast Membrane ◽  
Individual Subunit ◽  
Plastid Protein ◽  
Chloroplast Envelope Membrane ◽  
Shock Proteins

Import of preproteins into chloroplasts is an essential process, requiring two major multisubunit protein complexes that are embedded in the outer and inner chloroplast envelope membrane. Both the translocon of the outer chloroplast membrane (Toc), as well as the translocon of the inner chloroplast membrane (Tic) have been studied intensively with respect to their individual subunit compositions, functions and regulations. Recent advances in crystallography have increased our understanding of the operation of these proteins in terms of their interactions and regulation by conformational switching. Several subdomains of components of the Toc translocon have been studied at the structural level, among them the polypeptide transport-associated (POTRA) domain of the channel protein Toc75 and the GTPase domain of Toc34. In this review, we summarize and discuss the insight that has been gained from these structural analyses. In addition, we present the crystal structure of the Toc64 tetratrico-peptide repeat (TPR) domain in complex with the C-terminal domains of the heat-shock proteins (Hsp) Hsp90 and Hsp70.

scholarly journals The Role of Tetrapyrrole- and GUN1-Dependent Signaling on Chloroplast Biogenesis

Plants ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 196
Author(s):  
Takayuki Shimizu ◽  
Tatsuru Masuda
Keyword(s):  
Protein Import ◽  
Nuclear Gene ◽  
Retrograde Signaling ◽  
Chloroplast Biogenesis ◽  
Plastid Development ◽  
Nuclear Gene Expression ◽  
Coordinated Expression ◽  
Plastid Protein ◽  
Working Hypotheses

Chloroplast biogenesis requires the coordinated expression of the chloroplast and nuclear genomes, which is achieved by communication between the developing chloroplasts and the nucleus. Signals emitted from the plastids, so-called retrograde signals, control nuclear gene expression depending on plastid development and functionality. Genetic analysis of this pathway identified a set of mutants defective in retrograde signaling and designated genomes uncoupled (gun) mutants. Subsequent research has pointed to a significant role of tetrapyrrole biosynthesis in retrograde signaling. Meanwhile, the molecular functions of GUN1, the proposed integrator of multiple retrograde signals, have not been identified yet. However, based on the interactions of GUN1, some working hypotheses have been proposed. Interestingly, GUN1 contributes to important biological processes, including plastid protein homeostasis, through transcription, translation, and protein import. Furthermore, the interactions of GUN1 with tetrapyrroles and their biosynthetic enzymes have been revealed. This review focuses on our current understanding of the function of tetrapyrrole retrograde signaling on chloroplast biogenesis.

scholarly journals Plastid protein import and sorting: different paths to the same compartments

2008 ◽  
Vol 11 (6) ◽  
pp. 585-592 ◽  
Author(s):  
Kenneth Cline ◽  
Carole Dabney-Smith
Keyword(s):  
Protein Import ◽  
Plastid Protein

scholarly journals Genome-Based Reconstruction of the Protein Import Machinery in the Secondary Plastid of a Chlorarachniophyte Alga

2012 ◽  
Vol 11 (3) ◽  
pp. 324-333 ◽  
Author(s):  
Yoshihisa Hirakawa ◽  
Fabien Burki ◽  
Patrick J. Keeling
Keyword(s):  
Protein Import ◽  
Intermembrane Space ◽  
Content Type ◽  
Green Algal ◽  
Secondary Plastid ◽  
Plastid Proteins ◽  
Red Algal ◽  
Plastid Protein ◽  
Secondary Plastids ◽  
Envelope Membranes

ABSTRACT Most plastid proteins are encoded by their nuclear genomes and need to be targeted across multiple envelope membranes. In vascular plants, the translocons at the outer and inner envelope membranes of chloroplasts (TOC and TIC, respectively) facilitate transport across the two plastid membranes. In contrast, several algal groups harbor more complex plastids, the so-called secondary plastids, which are surrounded by three or four membranes, but the plastid protein import machinery (in particular, how proteins cross the membrane corresponding to the secondary endosymbiont plasma membrane) remains unexplored in many of these algae. To reconstruct the putative protein import machinery of a secondary plastid, we used the chlorarachniophyte alga Bigelowiella natans , whose plastid is bounded by four membranes and still possesses a relict nucleus of a green algal endosymbiont (the nucleomorph) in the intermembrane space. We identified nine homologs of plant-like TOC/TIC components in the recently sequenced B. natans nuclear genome, adding to the two that remain in the nucleomorph genome ( B. natans TOC75 [BnTOC75] and BnTIC20). All of these proteins were predicted to be localized to the plastid and might function in the inner two membranes. We also show that the homologs of a protein, Der1, that is known to mediate transport across the second membrane in the several lineages with secondary plastids of red algal origin is not associated with plastid protein targeting in B. natans . How plastid proteins cross this membrane remains a mystery, but it is clear that the protein transport machinery of chlorarachniophyte plastids differs from that of red algal secondary plastids.

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