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Simon Geir Møller

Publications and source records attributed to Simon Geir Møller.

13 recordsLinked to original sources
PubMed2006

Plastid division: evolution, mechanism and complexity.

BACKGROUND: The continuity of chloroplasts is maintained by division of pre-existing chloroplasts. Chloroplasts originated as bacterial endosymbionts; however, the majority of bacterial division factors are absent from chloroplasts and the eukaryotic host has added several new components. For example, the ftsZ gene has been duplicated and modified, and the Min system has retained MinE and MinD but lost MinC, acquiring at least one new component ARC3. Further, the mechanism has evolved to include two members of the dynamin protein family, ARC5 and FZL, and plastid-dividing (PD) rings were most probably added by the eukaryotic host. SCOPE: Deciphering how the division of plastids is coordinated and controlled by nuclear-encoded factors is key to our understanding of this important biological process. Through a number of molecular-genetic and biochemical approaches, it is evident that FtsZ initiates plastid division where the coordinated action of MinD and MinE ensures correct FtsZ (Z)-ring placement. Although the classical FtsZ antagonist MinC does not exist in plants, ARC3 may fulfil this role. Together with other prokaryotic-derived proteins such as ARC6 and GC1 and key eukaryotic-derived proteins such as ARC5 and FZL, these proteins make up a sophisticated division machinery. The regulation of plastid division in a cellular context is largely unknown; however, recent microarray data shed light on this. Here the current understanding of the mechanism of chloroplast division in higher plants is reviewed with an emphasis on how recent findings are beginning to shape our understanding of the function and evolution of the components. CONCLUSIONS: Extrapolation from the mechanism of bacterial cell division provides valuable clues as to how the chloroplast division process is achieved in plant cells. However, it is becoming increasingly clear that the highly regulated mechanism of plastid division within the host cell has led to the evolution of features unique to the plastid division process.

Arabidopsis Proteins↗
PubMed2006

AtSufE is an essential activator of plastidic and mitochondrial desulfurases in Arabidopsis.

Iron-sulfur (Fe-S) clusters are vital prosthetic groups for Fe-S proteins involved in fundamental processes such as electron transfer, metabolism, sensing and signaling. In plants, sulfur (SUF) protein-mediated Fe-S cluster biogenesis involves iron acquisition and sulfur mobilization, processes suggested to be plastidic. Here we have shown that AtSufE in Arabidopsis rescues growth defects in SufE-deficient Escherichia coli. In contrast to other SUF proteins, AtSufE localizes to plastids and mitochondria interacting with the plastidic AtSufS and mitochondrial AtNifS1 cysteine desulfurases. AtSufE activates AtSufS and AtNifS1 cysteine desulfurization, and AtSufE activity restoration in either plastids or mitochondria is not sufficient to rescue embryo lethality in AtSufE loss-of-function mutants. AtSufE overexpression induces AtSufS and AtNifS1 expression, which in turn leads to elevated cysteine desulfurization activity, chlorosis and retarded development. Our data demonstrate that plastidic and mitochondrial Fe-S cluster biogenesis shares a common, essential component, and that AtSufE acts as an activator of plastidic and mitochondrial desulfurases in Arabidopsis.

Arabidopsis↗
PubMed2005

The plastid division protein AtMinD1 is a Ca2+-ATPase stimulated by AtMinE1.

Bacteria and plastids divide symmetrically through binary fission by accurately placing the division site at midpoint, a process initiated by FtsZ polymerization, which forms a Z-ring. In Escherichia coli precise Z-ring placement at midcell depends on controlled oscillatory behavior of MinD and MinE: In the presence of ATP MinD interacts with the FtsZ inhibitor MinC and migrates to the membrane where the MinD-MinC complex recruits MinE, followed by MinD-mediated ATP hydrolysis and membrane release. Although correct Z-ring placement during Arabidopsis plastid division depends on the precise localization of the bacterial homologs AtMinD1 and AtMinE1, the underlying mechanism of this process remains unknown. Here we have shown that AtMinD1 is a Ca2+-dependent ATPase and through mutation analysis demonstrated the physiological importance of this activity where loss of ATP hydrolysis results in protein mislocalization within plastids. The observed mislocalization is not due to disrupted AtMinD1 dimerization, however; the active site AtMinD1(K72A) mutant is unable to interact with the topological specificity factor AtMinE1. We have shown that AtMinE1, but not E. coli MinE, stimulates AtMinD1-mediated ATP hydrolysis, but in contrast to prokaryotes stimulation occurs in the absence of membrane lipids. Although AtMinD1 appears highly evolutionarily conserved, we found that important biochemical and cell biological properties have diverged. We propose that correct intraplastidic AtMinD1 localization is dependent on AtMinE1-stimulated, Ca2+-dependent AtMinD1 ATP hydrolysis, ultimately ensuring precise Z-ring placement and symmetric plastid division.

Adenosine Triphosphatases↗
PubMed2005

Plastid division is mediated by combinatorial assembly of plastid division proteins.

Plastids arise by division from pre-existing organelles, and with the recent characterization of several new components of plastid division our understanding of the division process in higher plants has improved dramatically. However, it is still not known how these different protein components act together during division. Here we analyse protein-protein interactions between all known stromal plastid division proteins. Using a combination of quantitative yeast two-hybrid assays, in planta co-localization studies, fluorescence resonance energy transfer and bimolecular fluorescence complementation assays we show that these proteins do not act in isolation but rather in protein complexes to govern appropriate plastid division. We have previously shown that AtMinD1 forms functional homodimers and we show here that in addition to homodimerization AtMinD1 also interacts with AtMinE1. Furthermore, AtMinE1 has the ability to homodimerize. We also demonstrate that proteins from both FtsZ families (AtFtsZ1-1 and AtFtsZ2-1) not only interact with themselves but also with each other, and we show that these interactions are not dependent on correct Z-ring formation. Further to this we demonstrate that ARC6 specifically interacts with the core domain of AtFtsZ2-1, but not with AtFtsZ1-1, providing in planta evidence for a functional difference between the two FtsZ protein families in plants. Our studies have enabled us to construct a meaningful intraplastidic protein-protein interaction map of all known stromal plastid division proteins in Arabidopsis.

Arabidopsis Proteins↗
PubMed2004

AtNAP1 represents an atypical SufB protein in Arabidopsis plastids.

The assembly of iron-sulfur (Fe-S) clusters involves several pathways and in prokaryotes the mobilization of the sulfur (SUF) system is paramount for Fe-S biogenesis and repair during oxidative stress. The prokaryotic SUF system consists of six proteins: SufC is an ABC/ATPase that forms a complex with SufB and SufD, SufA acts as a scaffold protein, and SufE and SufS are involved in sulfur mobilization from cysteine. Despite the importance of Fe-S proteins in higher plant plastids, little is known regarding plastidic Fe-S cluster assembly. We have recently shown that Arabidopsis harbors an evolutionary conserved plastidic SufC protein (AtNAP7) capable of hydrolyzing ATP and interacting with the SufD homolog AtNAP6. Based on this and the prokaryotic SUF system we speculated that a SufB-like protein may exist in plastids. Here we demonstrate that the Arabidopsis plastid-localized SufB homolog AtNAP1 can complement SufB deficiency in Escherichia coli during oxidative stress. Furthermore, we demonstrate that AtNAP1 can interact with AtNAP7 inside living chloroplasts suggesting the presence of a plastidic AtNAP1.AtNAP6.AtNAP7 complex and remarkable evolutionary conservation of the SUF system. However, in contrast to prokaryotic SufB proteins with no associated ATPase activity we show that AtNAP1 is an iron-stimulated ATPase and that AtNAP1 is capable of forming homodimers. Our results suggest that AtNAP1 represents an atypical plastidic SufB-like protein important for Fe-S cluster assembly and for regulating iron homeostasis in Arabidopsis.

Adenosine Triphosphatases↗
PubMed2004

A homolog of Albino3/OxaI is essential for thylakoid biogenesis in the cyanobacterium Synechocystis sp. PCC6803.

YidC/OxaI play essential roles in the insertion of a wide range of membrane proteins in Eschericha coli and mitochondria, respectively. In contrast, the chloroplast thylakoid homolog Albino3 (Alb3) facilitates the insertion of only a specialized subset of proteins, and the vast majority insert into thylakoids by a pathway that is so far unique to chloroplasts. In this study, we have analyzed the role of Alb3 in the cyanobacterium Synechocystis sp. PCC6803, which contains internal thylakoids that are similar in some respects to those of chloroplasts. The single alb3 gene (slr1471) was disrupted by the introduction of an antibiotic cassette, and photoautotrophic growth resulted in the generation of a merodiploid species (but not full segregation), indicating an essential role for Alb3 in maintaining the photosynthetic apparatus. Thylakoid organization is lost under these conditions, and the levels of photosynthetic pigments fall to approximately 40% of wild-type levels. Photosynthetic electron transport and oxygen evolution are reduced by a similar extent. Growth on glucose relieves the selective pressure to maintain photosynthetic competence, and under these conditions, the cells become completely bleached, again indicating that Alb3 is essential for thylakoid biogenesis. Full segregation could not be achieved under any growth regime, strongly suggesting that the slr1471 open reading frame is essential for cell viability.

Arabidopsis Proteins↗
PubMed2004

AtNAP7 is a plastidic SufC-like ATP-binding cassette/ATPase essential for Arabidopsis embryogenesis.

In bacteria, yeast, and mammals, iron-sulfur (Fe-S) cluster-containing proteins are involved in numerous processes including electron transfer, metabolic reactions, sensing, signaling, and regulation of gene expression. In humans, iron-storage diseases such as X-linked sideroblastic anemia and ataxia are caused by defects in Fe-S cluster availability. The biogenesis of Fe-S clusters involves several pathways, and in bacteria, the SufABCDSE operon has been shown to play a vital role in Fe-S biogenesis and repair during oxidative stress. Although Fe-S proteins play vital roles in plants, Fe-S cluster biogenesis and maintenance and physiological consequences of dysfunctional Fe-S cluster assembly remains obscure. Here we report that Arabidopsis plants deficient for the SufC homolog AtNAP7 show lethality at the globular stage of embryogenesis. AtNAP7 is expressed in developing embryos and in apical, root, and floral meristems and encodes an ATP-binding cassette/ATPase that can partially rescue growth defects in an Escherichia coli SufC mutant during oxidative stress. AtNAP7 is plastid-localized, and mutant embryos contain abnormal developing plastids with disorganized thylakoid structures. We found that AtNAP7 can interact with AtNAP6, a plastidic Arabidopsis SufD homolog, and because Arabidopsis plastids also harbor SufA, SufB, SufS, and SufE homologs, plastids probably contain a complete SUF system. Our results imply that AtNAP7 represents a conserved SufC protein involved in the biogenesis and/or repair of oxidatively damaged Fe-S clusters and suggest an important role for plastidic Fe-S cluster maintenance and repair during Arabidopsis embryogenesis.

ATP-Binding Cassette Transporters↗
PubMed2004

GIANT CHLOROPLAST 1 is essential for correct plastid division in Arabidopsis.

Plastids are vital plant organelles involved in many essential biological processes. Plastids are not created de novo but divide by binary fission mediated by nuclear-encoded proteins of both prokaryotic and eukaryotic origin. Although several plastid division proteins have been identified in plants, limited information exists regarding possible division control mechanisms. Here, we describe the identification of GIANT CHLOROPLAST 1 (GC1), a new nuclear-encoded protein essential for correct plastid division in Arabidopsis. GC1 is plastid-localized and is anchored to the stromal surface of the chloroplast inner envelope by a C-terminal amphipathic helix. In Arabidopsis, GC1 deficiency results in mesophyll cells harbouring one to two giant chloroplasts, whilst GC1 overexpression has no effect on division. GC1 can form homodimers but does not show any interaction with the Arabidopsis plastid division proteins AtFtsZ1-1, AtFtsZ2-1, AtMinD1, or AtMinE1. Analysis reveals that GC1-deficient giant chloroplasts contain densely packed wild-type-like thylakoid membranes and that GC1-deficient leaves exhibit lower rates of CO(2) assimilation compared to wild-type. Although GC1 shows similarity to a putative cyanobacterial SulA cell division inhibitor, our findings suggest that GC1 does not act as a plastid division inhibitor but, rather, as a positive factor at an early stage of the division process.

Amino Acid Sequence↗
PubMed2004

Chloroplast division site placement requires dimerization of the ARC11/AtMinD1 protein in Arabidopsis.

Chloroplast division is mediated by the coordinated action of a prokaryote-derived division system(s) and a host eukaryote-derived membrane fission system(s). The evolutionary conserved prokaryote-derived system comprises several nucleus-encoded proteins, two of which are thought to control division site placement at the midpoint of the organelle: a stromal ATPase MinD and a topological specificity factor MinE. Here, we show that arc11, one of 12 recessive accumulation and replication of chloroplasts (arc) mutants in Arabidopsis, contains highly elongated and multiple-arrayed chloroplasts in developing green tissues. Genomic sequence analysis revealed that arc11 contains a missense mutation in alpha-helix 11 of the chloroplast-targeted AtMinD1 changing an Ala at position 296 to Gly (A296G). Introduction of wild-type AtMinD1 restores the chloroplast division defects of arc11 and quantitative RT-PCR analysis showed that the degree of complementation was highly dependent on transgene expression levels. Overexpression of the mutant ARC11/AtMinD1 in transgenic plants results in the inhibition of chloroplast division, showing that the mutant protein has retained its division inhibition activity. However, in contrast to the defined and punctate intraplastidic localization patterns of an AtMinD1-YFP fusion protein, the single A296G point mutation in ARC11/AtMinD1 results in aberrant localization patterns inside chloroplasts. We further show that AtMinD1 is capable of forming homodimers and that this dimerization capacity is abolished by the A296G mutation in ARC11/AtMinD1. Our data show that arc11 is a loss-of-function mutant of AtMinD1 and suggest that the formation of functional AtMinD1 homodimers is paramount for appropriate AtMinD1 localization, ultimately ensuring correct division machinery placement and chloroplast division in plants.

Amino Acid Sequence↗
PubMed2003

Membrane-specific targeting of green fluorescent protein by the Tat pathway in the cyanobacterium Synechocystis PCC6803.

The transport and sorting of extracytoplasmic proteins in cyanobacteria is made complex by the presence of a highly differentiated membrane system. Proteins destined for the periplasm and thylakoid lumen are initially transported by Sec- and Tat-type pathways but little is known of the mechanisms that ultimately direct them to the correct destinations. We have generated a Synechocystis PCC6803 transformant that expresses a fusion protein comprising the Tat-specific targeting signal of Escherichia coli TorA linked to green fluorescent protein (GFP). Immunoblotting indicates the presence of mature-size GFP but no precursor form, demonstrating that efficient translocation has taken place. Confocal microscopy and immunogold electron microscopy reveal GFP to be almost exclusively located in the periplasm, with almost no protein evident in the thylakoid network. These data point to the operation of highly effective sorting pathways for soluble proteins in this cyanobacterium. The observed sorting of the GFP suggests that either (a) the Tat apparatus is located only in the plasma membrane or (b) the TorA-GFP is targeted across either membrane but the GFP is subsequently directed to the periplasm, perhaps by a default sorting pathway to this compartment.

Bacterial Proteins↗
PubMed2003

The novel MYB protein EARLY-PHYTOCHROME-RESPONSIVE1 is a component of a slave circadian oscillator in Arabidopsis.

Using fluorescent differential display, we identified, from approximately 8000 displayed bands, a DNA fragment showing rapid induction in response to red light irradiation. This EARLY-PHYTOCHROME-RESPONSIVE1 gene (EPR1) encodes a novel nucleus-localized MYB protein harboring a single MYB domain that is highly similar to the circadian oscillator proteins CCA1 and LHY. EPR1 is regulated by both phytochrome A and phytochrome B, and the red-light induction of EPR1 is not inhibited by cycloheximide, demonstrating that EPR1 represents a primary phytochrome-responsive gene. Our results show that EPR1 overexpression results in enhanced far-red light-induced cotyledon opening and delayed flowering. In wild-type Arabidopsis plants grown in continuous light, the EPR1 transcript exhibits circadian rhythmicity similar to that of CCA1 and LHY. Moreover, EPR1 suppresses its own expression, suggesting that this protein is part of a regulatory feedback loop. Constitutive expression of CCA1 and LHY results in the loss of EPR1 rhythmicity, whereas increased levels of EPR1 have no effect on the central oscillator. We propose that EPR1 is a component of a slave oscillator that contributes to the refinement of output pathways, ultimately mediating the correct oscillatory behavior of target genes.

Amino Acid Sequence↗
PubMed2002

Chemical regulated production of cDNAs from genomic DNA fragments in plants.

We have developed a new chemical inducible genetic system that allows for the isolation of any cDNA molecule from in vitro generated genomic transgenes in transgenic plants. This system, termed regulated in vivo cDNA generation (RIDE), permits both targeted isolation of individual full-length cDNA molecules and random isolation of any partial or full-length cDNA from in planta genomic libraries. The RIDE system makes use of the 17-beta estradiol-inducible promoter system linked to intron donor and acceptor sites in a new binary vector configuration. In transgenic Arabidopsis and tobacco plants, we show that the RIDE system can isolate low-abundance full-length cDNAs previously unattainable by conventional means at high efficiencies (75-85%). The ability to randomly isolate individual exons and exons spliced together from genomic libraries in planta suggest that this system can be used for the isolation of any cDNA molecules. The RIDE system thus appears to be an efficient and versatile system for the generation of potentially any cDNA molecule. Moreover, the ORF structural data generated will be of value in both verifying and correcting computational ORF predications in the databases available to the scientific community.

Arabidopsis↗