Chloroplasts, endosymbiotic organelles in plant and algal cells, are essential for photosynthesis and metabolism. Their evolution involved extensive gene transfer to the nuclear genome, necessitating a complex system for protein import. This process involves coordinated gene expression, translation, and protein transport, utilizing multi-member protein complexes in the cytosol, envelope membranes, and stroma. The mechanism relies on chaperones, receptors, channels, and regulatory elements for accurate targeting, transport, and folding.

Triose phosphates (TPs) are the primary products of photosynthetic CO 2 fixation in chloroplasts, which need to be exported into the cytosol across the chloroplast inner envelope (IE) and outer envelope (OE) membranes to sustain plant growth. While transport across the IE is well understood, the mode of action of the transporters in the OE remains unclear. Here we present the high-resolution nuclear magnetic resonance (NMR) structure of the outer envelope protein 21 (OEP21) from garden pea, the main exit pore for TPs in C 3 plants. OEP21 is a cone-shaped β-barrel pore with a highly positively charged interior that enables binding and translocation of negatively charged metabolites in a competitive manner, up to a size of ~1 kDa. ATP stabilizes the channel and keeps it in an open state. Despite the broad substrate selectivity of OEP21, these results suggest that control of metabolite transport across the OE might be possible.

The plastid outer envelope (OE) is a mixture of components inherited from their prokaryotic ancestor like galactolipids, carotenoids and porin type ion channels supplemented with eukaryotic inventions to make the endosymbiotic process successful as well as to control plastid biogenesis and differentiation. In this review we wanted to highlight the importance of the OE proteins and its evolutionary origin. For a long time, the OE was thought to be a diffusion barrier only, but with the recent discoveries of all kinds of different proteins in the OE it has been shown that the OE can modulate various functions within the cell. The phenotypic changes show that channels like the outer envelope proteins OEP40, OEP16 or JASSY have a pronounced ion selectivity that cannot be replaced by other ion channels present in the OE. Eukaryotic additions, like the GTPase receptors Toc33 and Toc159 or the ubiquitin proteasome system for chloroplast protein quality control, round up the profile of the OE.

Male-sterile lines play important roles in plant breeding to obtain hybrid vigour. The male sterility Lembke (MSL) system is a thermosensitive genic male sterility system of Brassica napus and is one of the main systems used in European rapeseed breeding. Interestingly, the MSL system shows high similarity to the 9012AB breeding system from China, including the ability to revert to fertile in high temperature conditions. Here we demonstrate that the MSL system is regulated by the same restorer of fertility gene BnaC9-Tic40 as the 9012AB system, which is related to the translocon at the inner envelope membrane of chloroplasts 40 (TIC40) from Arabidopsis. The male sterility gene of the MSL system was also identified to encode a chloroplast-localized protein which we call BnChimera; this gene shows high sequence similarity to the sterility gene previously described for the 9012AB system. For the first time, a direct protein interaction between BnaC9-Tic40 and the BnChimera could be demonstrated. In addition, we identify the corresponding amino acids that mediate this interaction and suggest how BnaC9-Tic40 acts as the restorer of fertility. Using an RNA-seq approach, the effects of heat treatment on the male fertility restoration of the C545 MSL system line were investigated. These data demonstrate that many pollen developmental pathways are affected by higher temperatures. It is hypothesized that heat stress reverses the male sterility via a combination of slower production of cell wall precursors in plastids and a slower flower development, which ultimately results in fertile pollen. The potential breeding applications of these results are discussed regarding the use of the MSL system in producing thermotolerant fertile plants.

EDITORIAL article Front. Plant Sci., 01 March 2023Sec. Plant Physiology Volume 14 - 2023 | https://doi.org/10.3389/fpls.2023.1145680

In yeast (Saccharomyces cerevisiae) and human (Homo sapiens) mitochondria, Oxidase assembly protein1 (Oxa1) is the general insertase for protein insertion from the matrix side into the inner membrane while Cytochrome c oxidase assembly protein18 (Cox18/Oxa2) is specifically involved in the topogenesis of the complex IV subunit, Cox2. Arabidopsis (Arabidopsis thaliana) mitochondria contain four OXA homologs: OXA1a, OXA1b, OXA2a, and OXA2b. OXA2a and OXA2b are unique members of the Oxa1 superfamily, in that they possess a tetratricopeptide repeat (TPR) domain at their C termini. Here, we determined the role of OXA2a by studying viable mutant plants generated by partial complementation of homozygous lethal OXA2a transfer-DNA insertional mutants using the developmentally regulated ABSCISIC ACID INSENSITIVE3 (ABI3) promoter. The ABI3p:OXA2a plants displayed growth retardation due to a reduction in the steady-state abundances of both c-type cytochromes, cytochrome c 1 and cytochrome c. The observed reduction in the steady-state abundance of complex III could be attributed to cytochrome c 1 being one of its subunits. Expression of a soluble heme lyase from an organism with cytochrome c maturation system III could functionally complement the lack of OXA2a. This implies that OXA2a is required for the system I cytochrome c maturation of Arabidopsis. Due to the interaction of OXA2a with Cytochrome c maturation protein CcmF C-terminal-like protein (CCMFC) in a yeast split-ubiquitin based interaction assay, we propose that OXA2a aids in the membrane insertion of CCMFC, which is presumed to form the heme lyase component of the cytochrome c maturation pathway. In contrast with the crucial role played by the TPR domain of OXA2b, the TPR domain of OXA2a is not essential for its functionality.

The thylakoid membrane network inside chloroplasts harbours the protein complexes that are necessary for the light-dependent reactions of photosynthesis. Cellular processes for building and altering this membrane network are therefore essential for life on Earth. Nevertheless, detailed molecular processes concerning the origin and synthesis of the thylakoids remain elusive. Thylakoid biogenesis is strongly coupled to the processes of chloroplast differentiation. Chloroplasts develop from special progenitors called proplastids. As many of the needed building blocks such as lipids and pigments derive from the inner envelope, the question arises how these components are recruited to their target membrane. This review travels back in time to the beginnings of thylakoid membrane research to summarize findings, facts and fictions on thylakoid biogenesis and structure up to the present state, including new insights and future developments in this field.

Jasmonates are vital plant hormones that not only act in the stress response to biotic and abiotic influences, such as wounding, pathogen attack, and cold acclimation, but also drive developmental processes in cooperation with other plant hormones. The biogenesis of jasmonates starts in the chloroplast, where several enzymatic steps produce the jasmonate precursor 12-oxophytodienoic acid (OPDA) from α-linolenic acid. OPDA in turn is exported into the cytosol for further conversion into active jasmonates, which subsequently induces the expression of multiple genes in the nucleus. Despite its obvious importance, the export of OPDA across the chloroplast membranes has remained elusive. In this study, we characterized a protein residing in the chloroplast outer membrane, JASSY, which has proven indispensable for the export of OPDA from the chloroplast. We provide evidence that JASSY has channel-like properties and propose that it thereby facilitates OPDA transport. Consequently, a lack of JASSY in Arabidopsis leads to a deficiency in accumulation of jasmonic acids, which results in impaired expression of jasmonate target genes on exposure to various stresses. This results in plants that are more susceptible to pathogen attack and also exhibit defects in cold acclimation.

Plastoglobules are lipoprotein particles that are found in different types of plastids. They contain a very specific and specialized set of lipids and proteins. Plastoglobules are highly dynamic in size and shape, and are therefore thought to participate in adaptation processes during either abiotic or biotic stresses or transitions between developmental stages. They are suggested to function in thylakoid biogenesis, isoprenoid metabolism, and chlorophyll degradation. While several plastoglobular proteins contain identifiable domains, others provide no structural clues to their function. In this study, we investigate the role of plastoglobular protein 18 (PG18), which is conserved from cyanobacteria to higher plants. Analysis of a PG18 loss-of-function mutant in Arabidopsis thaliana demonstrated that PG18 plays an important role in thylakoid formation; the loss of PG18 results in impaired accumulation, assembly, and function of thylakoid membrane complexes. Interestingly, the mutant accumulated less chlorophyll and carotenoids, whereas xanthophyll cycle pigments were increased. Accumulation of photosynthetic complexes is similarly affected in both a Synechocystis and an Arabidopsis PG18 mutant. However, the ultrastructure of cyanobacterial thylakoids is not compromised by the lack of PG18, probably due to its less complex architecture.

During the biogenesis of the mitochondrial inner membrane, most nuclear-encoded inner membrane proteins are laterally released into the membrane by the TIM23 and the TIM22 machinery during their import into mitochondria. A subset of nuclear-encoded mitochondrial inner membrane proteins and all the mitochondrial-encoded inner membrane proteins use the Oxa machinery—which is evolutionarily conserved from the endosymbiotic bacterial ancestor of mitochondria—for membrane insertion. Compared to the mitochondria from other eukaryotes, plant mitochondria have several unique features, such as a larger genome and a branched electron transport pathway, and are also involved in additional cellular functions such as photorespiration and stress perception. This review focuses on the unique aspects of plant mitochondrial inner membrane protein insertion machinery, which differs from that in yeast and humans, and includes a case study on the biogenesis of Cox2 in yeast, humans, two plant species, and an algal species to highlight lineage-specific similarities and differences. Interestingly, unlike mitochondria of other eukaryotes but similar to bacteria and chloroplasts, plant mitochondria appear to use the Tat machinery for membrane insertion of the Rieske Fe/S protein.

Plant biologists often need to observe the growth behavior of their chosen species. To this end, the plants need constant environmental and stable light conditions, which are preferably variable in quantity and quality so that studies under different setups can be conducted. These requirements are met by climatic chambers featuring light emitting diodes (LED) lights, which can - in contrast to fluorescent lights - be set to different wavelengths. LEDs are energy conserving and emit virtually no heat even at light intensities, which often constitutes a problem with other light sources. The presented protocol provides a step-by-step guidance of how to program a climatic chamber equipped with variable LED lights as well as describing several approaches for in depth analysis of growth phenotypes. Depending on the experimental set-up various characteristics of the growing plants can be observed and analyzed. Here we describe how to determine fresh weight, leaf area, photosynthetic activity, and stomatal density. We demonstrate that in order to obtain reliable data and draw valid conclusions it is mandatory to use a sufficient number of individuals for statistical evaluation. Taking too few plants for this kind of analysis results in high statistical errors and consequently in less clear interpretations of the data.

Mitochondrial localized proteins are mostly synthesized in the cytosol and translocated across the outer mitochondrial membrane via the translocase of the outer membrane (TOM) complex. Although the channel protein is conserved among eukaryotes, the receptor proteins are more divergent and show features specific to the plant lineage. OM64, which is a paralogue of the chloroplast docking protein Toc64, is unique to plants. However, due to the presence of a cytosolic exposed TPR domain it might functionally replace yeast/mammalian Tom70, which is not found in plant mitochondria, by interacting with the C-terminal (M)EEVD motif of the heat shock proteins Hsp90 and Hsp70. In this study, we show that OM64 is phosphorylated within its TPR domain. Using isothermal titration calorimetry it could be demonstrated that phosphorylation reduces the binding affinity of OM64 to Hsp90. Moreover, in vivo expression of genes encoding different OM64 variants in planta revealed that phosphorylation of OM64 impairs the import efficiency of the mitochondrial preprotein pFAD, a subunits of the mitochondrial ATP synthase. In summary, our data provide significant insight into the fine-tuning mechanisms of mitochondrial protein import mediated by phosphorylation of the cytosolic exposed receptor protein OM64.

FZL is primarily localized to the chloroplast inner envelope and not to the thylakoids, but nevertheless affects the maintenance of thylakoid membranes and photosynthetic protein complexes.

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.

The evolutionarily conserved YidC/Oxa1/Alb3 proteins are involved in the insertion of membrane proteins in all domains of life. In plant mitochondria, individual knockouts of OXA1a, OXA2a, and OXA2b are embryo-lethal. In contrast to other members of the protein family, OXA2a and OXA2b contain a tetratricopeptide repeat (TPR) domain at the C-terminus. Here, the role of Arabidopsis (Arabidopsis thaliana) OXA2b was determined by using viable mutant plants that were generated by complementing homozygous lethal OXA2b T-DNA insertional mutants with a C-terminally truncated OXA2b lacking the TPR domain. The truncated-OXA2b-complemented plants displayed severe growth retardation due to a strong reduction in the steady-state abundance and enzyme activity of the mitochondrial respiratory chain complex IV. The TPR domain of OXA2b directly interacts with cytochrome c oxidase subunit 2, aiding in efficient membrane insertion and translocation of its C-terminus. Thus, OXA2b is crucial for the biogenesis of complex IV in plant mitochondria.

Protein import into chloroplasts is an essential process for plant survival. Numerous studies in recent years have revealed many facts about the components involved and mechanistic features, but have also turned up some controversies. Especially the composition and function of the Tic (translocon at the inner envelope of chloroplasts) complex(es) are vividly debated. Whereas the importance of one central Tic component, Tic110, was generally accepted, its molecular task is still being controversially discussed. Quite recently, a new Tic translocon was proposed to represent the general import machinery with Tic20 and chloroplast encoded Ycf1 (=Tic214) as central components (Kikuchi et al., 2013aKikuchi S. Bedard J. Hirano M. Hirabayashi Y. Oishi M. Imai M. Takase M. Ide T. Nakai M. Uncovering the protein translocon at the chloroplast inner envelope membrane.Science. 2013; 339: 571-574Crossref PubMed Scopus (234) Google Scholar). According to this new model, the majority of imported proteins travel via Tic214/Tic20 into chloroplasts. However, a whole clade in the plant kingdom, the monocotyledonous plants, and several species from the dicotyledonous branch, are lacking Ycf1, suggesting that this protein cannot be a general import component when so many plants can do without it (de Vries et al., 2015de Vries J. Sousa F.L. Bölter B. Soll J. Gould S.B. YCF1: a green TIC?.Plant Cell. 2015; 27: 1827-1833Crossref PubMed Scopus (87) Google Scholar). In Arabidopsis, Ycf1 is an essential protein and thus analyzing its knockout mutants is not an option. There is, however, an elegant possibility to study plants in the absence of Ycf1 by growing them on media containing inhibitors of plastid translation. To this end, we grew two different ecotypes of Arabidopsis thaliana, Col-0 and Jl-3, on MS medium with or without spectinomycin, which is a specific inhibitor of plastid translation (Wirmer and Westhof, 2006Wirmer J. Westhof E. Molecular contacts between antibiotics and the 30S ribosomal particle.Methods Enzymol. 2006; 415: 180-202Crossref PubMed Scopus (62) Google Scholar) (Figure 1A ). In general, Col-0 plants without spectinomycin grew slightly faster than Jl-3 plants. On spectinomycin, however, JL-3 seedlings developed better and were less stressed than Col-0 as judged by the presence of anthocyanins in the leaves, which corresponds to the observations of Parker et al., 2014Parker N. Wang Y. Meinke D. Natural variation in sensitivity to a loss of chloroplast translation in Arabidopsis.Plant Physiol. 2014; 166: 2013-2027Crossref PubMed Scopus (36) Google Scholar. To analyze plastid protein content, total extract was isolated from equal amounts of plant material. Plants from plates without spectinomycin were harvested after 3 weeks, whereas those from plates containing spectinomycin needed to grow for 4–5 weeks until they reached a comparable size. Protein composition was expected to be very different, thus loading for the immuno blots was done according to a Coomassie stained gel (Figure 1B) rather than measuring total protein content. We did not aim for the results to be quantifiable, but rather to demonstrate the presence or absence of nuclear-encoded plastid proteins. The main proteins present in total extracts from green plants, the large (LSU) and small (SSU) subunits of Rubisco, as well as the light harvesting complex protein (LHC), are indicated in the figure and are missing in the white plants. Figure 1C–1G (C, outer envelope proteins; D, inner envelope proteins; E, stromal proteins; F, thylakoid proteins; G, cytosolic protein) show immuno blots probed with the indicated antibodies. Figure 1C clearly depicts that the outer envelope protein OEP16 is present in green as well as in white plants. This protein is inserted independent of the general import translocon and can consequently serve as an internal control (Pohlmeyer et al., 1997Pohlmeyer K. Soll J. Steinkamp T. Hinnah S. Wagner R. Isolation and characterization of an amino acid-selective channel protein present in the chloroplastic outer envelope membrane.Proc. Natl. Acad. Sci. USA. 1997; 94: 9504-9509Crossref PubMed Scopus (101) Google Scholar). Toc75, however, was shown to depend on the general import machinery (Inoue and Keegstra, 2003Inoue K. Keegstra K. A polyglycine stretch is necessary for proper targeting of the protein translocation channel precursor to the outer envelope membrane of chloroplasts.Plant J. 2003; 34: 661-669Crossref PubMed Scopus (76) Google Scholar) and is equally present in green and in white plants (Figure 1D). Similarly, the highly abundant inner envelope protein Tic110 is efficiently imported into plastids. The same behavior can be observed for the inner envelope constituents Tic40, Iep37, and Fax1, all of which feature classical transit peptides and are imported by the general import pathway. Most importantly, however, this occurred in the absence of detectable amounts of Ycf1 (Figure 1D, upper panel). Strikingly, Tic20, which was isolated in a complex with Ycf1 (Kikuchi et al., 2013aKikuchi S. Bedard J. Hirano M. Hirabayashi Y. Oishi M. Imai M. Takase M. Ide T. Nakai M. Uncovering the protein translocon at the chloroplast inner envelope membrane.Science. 2013; 339: 571-574Crossref PubMed Scopus (234) Google Scholar), is also not detectable, suggesting that assembly of these two proteins is interdependent, and a feedback mechanism from the chloroplast to the nucleus and/or cytosol prevents synthesis or accumulation of Tic20. Tic62, which is a specific interaction partner of the FNR, is strongly reduced in white plants. The same holds true for FNR itself, which is a photosynthetic protein and clearly not needed in albinotic plants. As could already be deduced from the Coomassie stained gel, the small subunit of Rubisco is absent, most likely due to feedback from the plastid that the large subunit cannot be synthesized, and therefore no complex assembly can be achieved. The thylakoid proteins Cytf and D1 seem completely absent; D1 is plastid encoded and cannot be translated and therefore serves as an internal standard for the effectiveness of the spectinomycin treatment, whereas Cytf (PetA) can obviously not be integrated into any thylakoid membrane in the white plants. In the stroma, the housekeeping protein Ndpk2 is clearly present, whereas FBPase and GOGAT are very much reduced. Acc2, the large eukaryotic form of the fatty acid synthase, is not only present but seems upregulated in plants containing no detectable Ycf1. Since we used an anti-biotin serum for detection of Acc2, we could not unequivocally say that the band at 230 kDa represents Acc2 rather than Acc1, which is expressed in the cytosol, whereas Acc2 carries an N-terminal extension that could function as a chloroplast transit peptide (Parker et al., 2014Parker N. Wang Y. Meinke D. Natural variation in sensitivity to a loss of chloroplast translation in Arabidopsis.Plant Physiol. 2014; 166: 2013-2027Crossref PubMed Scopus (36) Google Scholar). To clarify this, plastids were isolated and evaluated in comparison with total extract (Figure 1H). The cytosolic control, Aha1 (Fellerer et al., 2011Fellerer C. Schweiger R. Schongruber K. Soll J. Schwenkert S. Cytosolic HSP90 cochaperones HOP and FKBP interact with freshly synthesized chloroplast preproteins of Arabidopsis.Mol. Plant. 2011; 4: 1133-1145Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar), demonstrates the absence of cytosolic protein from the plastid preparation so that the band recognized by the biotin antibody can clearly be assigned to plastidial Acc2, which only appears when Ycf1 is below the detection limit. This suggests that Ycf1 could play a role in the assembly of plastid ACCase, which upon growth on spectinomycin lacks the essential plastid encoded subunit AccD (Sasaki et al., 1993Sasaki Y. Hakamada K. Suama Y. Nagano Y. Furusawa I. Matsuno R. Chloroplast-encoded protein as a subunit of acetyl-CoA carboxylase in pea plant.J. Biol. Chem. 1993; 268: 25118-25123PubMed Google Scholar). To complement for that loss, the second large eukaryotic isoform Acc2, which is usually very low abundant in comparison with the main isoform Acc1, could be upregulated and targeted to plastids, so that fatty acid synthesis can be performed. This assumption is supported by the somewhat increased presence of Fax1, a fatty acid transport protein mediating export of fatty acids (Li et al., 2015Li N. Gügel I.L. Giavalisco P. Zeisler V. Schreiber L. Soll J. Philippar K. FAX1, a novel membrane protein mediating plastid fatty acid export.PLoS Biol. 2015; 13: e1002053Crossref PubMed Scopus (127) Google Scholar). When we analyzed mRNA expression of selected genes, we found that the general response of Col-0 to spectinomycin is very different from Jl-3: Col-0 showed upregulated mRNA expression of the examined nuclear- and plastid-encoded genes, including ACC2, whereas JL-3 exhibited downregulated expression of the analyzed mRNAs with the notable exception of ACC2 (Supplemental Table 2). In contrast, the respective encoded proteins are either present in approximately equal amounts or absent in both ecotypes. Thus, RNA expression analysis is unsuitable to draw any conclusions about protein synthesis and their subsequent import. Our results show that Ycf1/Tic20 possibly cannot constitute the general import machinery, since in Arabidopsis plants with no detectable amounts of both proteins, import of plastid proteins is still maintained. In contrast to Ycf1/Tic20, Tic110 is found in the white plastids in approximately equal amounts compared with the normal green ones (Figure 1H), indicating that it could be indispensable for plastid import. This notion is supported by the observation that already the heterozygous tic110 mutant shows a clear growth phenotype (Kovacheva et al., 2005Kovacheva S. Bedard J. Patel R. Dudley P. Twell D. Rios G. Koncz C. Jarvis P. In vivo studies on the roles of Tic110, Tic40 and Hsp93 during chloroplast protein import.Plant J. 2005; 41: 412-428Crossref PubMed Scopus (156) Google Scholar). A function of Ycf1/Tic20 in import cannot be excluded at this point, but although both proteins are essential for plant growth, we can clearly conclude from the presented data that neither protein is mainly responsible for import of nuclear-encoded plastid proteins. During revision of this manuscript, Parker et al., 2016Parker N. Wang Y. Meinke D. Analysis of Arabidopsis accessions hypersensitive to a loss of chloroplast translation.Plant Physiol. 2016; 172: 1862-1875Crossref PubMed Scopus (19) Google Scholar reported that spectinomycin completely inhibits plastid translation and therefore Ycf1 synthesis (Parker et al., 2016Parker N. Wang Y. Meinke D. Analysis of Arabidopsis accessions hypersensitive to a loss of chloroplast translation.Plant Physiol. 2016; 172: 1862-1875Crossref PubMed Scopus (19) Google Scholar). In addition, Köhler et al., 2016Köhler D. Helm S. Agne B. Baginsky S. Importance of translocon subunit Tic56 for rRNA processing and chloroplast ribosome assembly.Plant Physiol. 2016; https://doi.org/10.1104/pp.16.01393Crossref Scopus (21) Google Scholar described mass spectrometric analyses of plants grown on spectinomycin, where ycf1 was non-detectable (Köhler et al., 2016Köhler D. Helm S. Agne B. Baginsky S. Importance of translocon subunit Tic56 for rRNA processing and chloroplast ribosome assembly.Plant Physiol. 2016; https://doi.org/10.1104/pp.16.01393Crossref Scopus (21) Google Scholar). Since mass spectrometry is much more sensitive than immuno blots, we could conclude that upon inhibition of plastid translation by spectinomycin Ycf1 is truly absent. Nevertheless, a number of imported plastid proteins were identified, confirming our immuno blot results and supporting the conclusion that plastid import is not dependent on Ycf1. This work was in part supported by the DFG through SFB-TR175 (projects B5 and B6) and the cluster of excellence CIPSM.

Comparative analyses of phenotypic and molecular traits of Arabidopsis thaliana grown under standardised conditions is still a challenge using climatic devices supplied with common light sources. These are in most cases fluorescent lights, which have several disadvantages such as heat production at higher light intensities, an invariable spectral output, and relatively rapid “ageing”. This results in non-desired variations of growth conditions and lowers the comparability of data acquired over extended time periods. In this study, we investigated the growth behaviour of Arabidopsis Col0 under different light conditions, applying fluorescent compared to LED lamps, and we conducted physiological as well as gene expression analyses. By changing the spectral composition and/or light intensity of LEDs we can clearly influence the growth behaviour of Arabidopsis and thereby study phenotypic attributes under very specific light conditions that are stable and reproducible, which is not necessarily given for fluorescent lamps. By using LED lights, we can also roughly mimic the sun light emission spectrum, enabling us to study plant growth in a more natural-like light set-up. We observed distinct growth behaviour under the different light regimes which was reflected by physiological properties of the plants. In conclusion, LEDs provide variable emission spectra for studying plant growth under defined, stable light conditions.

SLO4 is a mitochondrial PPR protein that is involved in editing nad4, possibly required for the efficient splicing of nad2 intron1.