Special Issue – Mini Review Editor-in-Chief’s choice 2000 Seeing Is Believing: On the Use of Image Databases for Visually Exploring Plant Organelle Dynamics Shoji Mano1,2, Tomoki Miwa3, Shuh-ichi Nishikawa4, Tetsuro Mimura5 and Mikio Nishimura1,2,∗ 1Department of Cell Biology, National Institute for Basic Biology, Okazaki, 444-8585 Japan of Basic Biology, School of Life Science, Graduate University for Advanced Studies, Okazaki, 444-8585 Japan 3Computer Laboratory, National Institute for Basic Biology, Okazaki, 444-8585 Japan 4Graduate School of Science, Nagoya University, Nagoya, 464-8602 Japan 5Department of Biology, Graduate School of Science, Kobe University, Kobe, 657-8501 Japan 2Department Organelle dynamics vary dramatically depending on cell type, developmental stage and environmental stimuli, so that various parameters, such as size, number and behavior, are required for the description of the dynamics of each organelle. Imaging techniques are superior to other techniques for describing organelle dynamics because these parameters are visually exhibited. Therefore, as the results can be seen immediately, investigators can more easily grasp organelle dynamics. At present, imaging techniques are emerging as fundamental tools in plant organelle research, and the development of new methodologies to visualize organelles and the improvement of analytical tools and equipment have allowed the largescale generation of image and movie data. Accordingly, image databases that accumulate information on organelle dynamics are an increasingly indispensable part of modern plant organelle research. In addition, image databases are potentially rich data sources for computational analyses, as image and movie data reposited in the databases contain valuable and significant information, such as size, number, length and velocity. Computational analytical tools support image-based data mining, such as segmentation, quantification and statistical analyses, to extract biologically meaningful information from each database and combine them to construct models. In this review, we outline the image databases that are dedicated to plant organelle research and present their potential as resources for image-based computational analyses. Keywords: Arabidopsis thaliana • Image database • Imaging • Organelle dynamics • Quantification • Systems biology. ∗Corresponding Abbreviations: BiFC, bimolecular fluorescence complementation; CLSM, confocal laser scanning microscope; ER, endoplasmic reticulum; EST, expressedsequence tag; FRAP, fluorescence recovery after photobleaching; FRET, fluorescence resonance energy transfer; GFP, green fluorescent protein; MRI, magnetic resonance imaging; RFP, red fluorescent protein; SNARE, soluble N-ethylmaleimide-sensitive factor attachment protein receptor. Introduction Technical advances in molecular biological procedures and the development of equipment have allowed the generation of a variety of information on a large-scale basis. In the field of plant biology, the groundwork of sequencing the whole genome of several plant species (Kaul et al. 2000, Goff et al. 2002, Yu et al. 2002, Tuskan et al. 2006, Jaillon et al. 2007, Nozaki et al. 2007) led to the accumulation of large data sets for these plants. These large data sets are deposited in databases that were constructed for storage, and used in complex analyses aimed at gene identification, annotation of protein function and prediction of protein localization. The development of analytical equipment and computational analytical tools has accelerated the implementation of new methodologies that use large amounts of data gleaned from databases. Therefore, the efficient extraction of biologically meaningful information from each database, as well as the integration of individual data, have become important for research purposes. author: E-mail, [email protected] Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128, available FREE online at www.pcp.oxfordjournals.org © The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: [email protected] Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. Image databases for plant organelle research Currently, a variety of public databases for plant biology are available. Table 1 displays parts of public databases for plant research. They are broadly categorized into four groups: (i) databases dedicated to specific plant species, (ii) databases for specific phenomena, (iii) organelle databases and (iv) integrative databases that compile several types of information from different organisms. These databases are mainly constructed based on compilations of genome and/or cDNA sequences and proteomic data. Most databases house text-based data, including nucleotide and/or amino acid sequences, which are used for further analyses, such as identification of genetic variation and gene clustering among several organisms; in contrast, some databases reposite numerical values. For example, databases of gene expression data from microarray analyses contain numerical information on the expression of each gene under various conditions, and databases that deal with results from proteomic analyses also contain numerical values (e.g., units of mass). In addition, as shown in Table 2, other databases gather image data that reveal protein localization and/or visualized organelles (Fig. 1A, Cutler et al. 2000, Damme et al. 2004, Brown et al. 2005, Koroleva et al. 2005, Li et al. 2006, Mano et al. 2008). Although these databases deal with static image data, some databases also collect movie data (Fig. 1B, Supplementary Movies 1, 2). Compared with textbased databases, these image databases exhibit an ability to display the dynamics of proteins, organelles and cells, which include their localization, size, number, morphology, movement and spatial distribution, because the data are immediately visible and accessible. Therefore, researchers can find information on the dynamics of a molecule/organelle more easily. Various technologies have been used to acquire image data from plant organelles. Several specific dyes, including Neutral red, MitoTracker and ER tracker, allow the effective staining of vacuoles (Carter et al. 2004), mitochondria (Arimura and Tsutsumi 2002) and the endoplasmic reticulum (ER) (Liu et al. 2007), respectively, and new specific dyes are currently being developed to cope with different excitation and/or emission wavelengths and to improve membrane permeability. In addition, fluorescent proteins, such as green fluorescent protein (GFP) and its derivatives, have contributed greatly to the field of imaging analysis, which includes visualization of plant organelles (Haseloff and Siemering 1998, Chudakov et al. 2005). Currently, almost all organelles in plant cells are visualized using GFP and its derivatives, and the dynamic pattern of subcellular structure is highlighted (Fig. 2). The improvement of existing fluorescent proteins, the discovery of new fluorescent proteins with different characteristics (Shaner et al. 2004, Kogure et al. 2006) and the development of new applications [such as fluorescence resonance energy transfer (FRET) and bimolecular fluorescence complementation (BiFC)] and of new vectors suitable for expression in plant cells (Nakagawa et al. 2007, Nelson et al. 2007) have revolutionized image analysis by enabling easier observation of dynamic subcellular processes in plant living cells. More detailed information on GFP is provided in other review articles (Haseloff and Siemering 1998, Chudakov et al. 2005, Berg and Beachy 2008). Image data contain rich information, such as size, length, morphology and velocity; thus, image databases represent potentially rich data sources for computational analyses aimed at extracting biologically meaningful information. Currently, various applications of computational analytical tools are used for image-based data mining and provide statistical information on organelle dynamics. The information contained in the image databases, together with other information such as expression data, can be incorporated into the construction of biological models. In other words, the use of image databases can represent a gateway resource for systems biology. Advanced imaging methodologies and equipment, such as microscopes, have become more easily applicable to the large-scale generation of image data; thus, image databases will become useful resources for the comprehensive understanding of plants. In this review, we outline the image databases dedicated to plant organelles and discuss their potential as image-based computational analysis tools for systems biology. Other public databases available for plant biology are well described in a recent review by Brady and Provart (2009). Visual representation of plant organelle dynamics Advantages of image databases The comprehensive understanding of individual plants requires the study of various biological aspects during their life cycle, which have been examined experimentally and/or via the use of databases. Each database has its advantages and limitations. Text-based descriptions are not necessarily the most adequate vehicle to address organelle dynamics, as organelle dynamics can vary dramatically depending on cell type, developmental stage and environmental stimuli. The description of organelle dynamics involves various parameters, such as size, length, velocity, direction and time. As a result, simple phenotypic patterns cannot be assumed in organelle dynamics, unlike genome sequence data; therefore, organelle dynamics information can be interpreted at various levels. In contrast, image and movie data are more adequate descriptors of these dynamics, as various parameters are visually exhibited in a single representation. Therefore, researchers can easily grasp organelle dynamics, as the results may be seen immediately. Live-cell imaging offers a wealth of information on the dynamics of proteins and organelles, such as movement, Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. 2001 S. Mano et al. Table 1 Vairous databases for plant science Name URL Comments TAIRa http://www.arabidopsis.org/ Arabidopsis thaliana RAP-DBb http://rapdb.dna.affrc.go.jp/ Oryza sativa Oryzabasec http://www.shigen.nig.ac.jp/rice/oryzabase/top/top.jsp Oryza sativa Specific plant-species database v1.1d http://genome.jgi-psf.org/Poptr1_1/Poptr1_1.home.html Populus trichocarpa Genoscopee http://www.genoscope.cns.fr/spip/Vitis-vinifera-e.html Vitis vinifera PHYSCObasef http://moss.nibb.ac.jp/ Physcomitrella patens LegumeBaseg http://www.shigen.nig.ac.jp/bean/lotusjaponicus/top/top.jsp Lotus japonicus miyakogusa.jp http://www.kazusa.or.jp/lotus/ Lotus japonicus Cyanidioschyzon merolae Genome Projecth http://merolae.biol.s.u-tokyo.ac.jp/ Cyanidioschyzon merolae SoyBasei http://soybase.org/ Glycine max http://rsoy.psc.riken.jp/ Glycine max http://genbank.vurv.cz/ewdb/default.htm Titicum L. Plantpromoter db 2.0l http://ppdb.gene.nagoya-u.ac.jp/cgi-bin/index.cgi Cis-element sequences PLACEm http://www.dna.affrc.go.jp/PLACE/ Cis-element sequences PlantsPn http://plantsp.genomics.purdue.edu/html/ Phosphorylation site PhosPhAt 2.2o http://phosphat.mpimp-golm.mpg.de/ Phosphorylation site TarBase v5cp http://diana.cslab.ece.ntua.gr/tarbase/ miRNA PlnTFDBq http://plntfdb.bio.uni-potsdam.de/v2.0/ Transcription factor TOBFACr http://compsysbio.achs.virginia.edu/tobfac/ Transcription factor PthoPlants http://www.pathoplant.de/ Plant-pathogen interactions Arabidopsis Mitochondrial Protein Databaset http://www.plantenergy.uwa.edu.au/applications/ampdb/index.html Mitochondria GOBASEu http://gobase.bcm.umontreal.ca/ Mitochondria, Chloroplast Chloroplast Genome Databasev http://chloroplast.cbio.psu.edu/ Chloroplast PeroxisomeDBw http://www.peroxisomedb.org/ Peroxisome AraPerox 1.2x http://www.araperox.uni-goettingen.de/ Peroxisome Populus trichocarpa Soybean full-length cDNA databasej The ECPGR Wheat Databasek Specific-aspcets database Organelle database Naviagatory http://bioweb.ucr.edu/Cellwall/index.pl Cell wall eSLDBz http://gpcr2.biocomp.unibo.it/esldb/index.htm Eukaryotic subcellular localization Organelle Genome Resources http://www.ncbi.nlm.nih.gov/genomes/GenomesHome. cgi?taxid=2759&hopt=html Chloroplasts, Mitochondria Cell Wall Integrative database NCBI http://www.ncbi.nlm.nih.gov/ DDBJ1 http://www.ddbj.nig.ac.jp/ TIGR http://www.tigr.org/db.shtml NASC http://arabidopsis.info/ PEDANT32 http://pedant.gsf.de/ Continued 2002 Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. Image databases for plant organelle research Table 1 Continued Name URL KEGG3 http://www.kegg.jp/ja/ Comments RIKEN https://database.riken.jp/sw/view#CRIB00158S000016?view=panel KAZUSA http://www.kazusa.or.jp/j/resources/database.html http://www.nias.affrc.go.jp/database/index.html NIAS aSwabreck bTanaka cKurata et al. (2008); et al. (2008); and Yamazaki (2006); dTuskan et al. (2006); eJaillon et al. (2007); fNishiyama et al. (2003); gSato et al. (2008); hNozaki et al. (2007); iSakata et al; (2009); jUmezawa et al. (2008); kRöder et al. (2002); lYamamoto and Obokata (2008); mHigo et al. (1999); nNühse et al. (2004); oHeazlewood et al. (2008); pPapadopoulos et al. (2009); qRiaño-Pachón et al. (2007); rRushton et al. (2008); sBülow et al. (2007); tHeazlewood et al. (2004); uO’Brien et al. (2009); vCui et al. (2006); wSchlüter et al. (2007); xReumann et al. (2004); yGirke et al. (2004); zPierleoni et al. (2007); 1Sugawara et al. (2009); 2Walter et al. (2009); 3Kanehisa et al. (2008) Table 2 Databases for dealing with image data in plant science Name URL Comments AtNoPDBa http://bioinf.scri.sari.ac.uk/cgi-bin/atnopdb/home Images of GFP-tagged proteins in nucleus in Arabidopsis thaliana FTFLPdbb, c http://gfp.stanford.edu/ Images of GFP-tagged proteins in various organelles in Arabidopsis thaliana Plant Cell Imagingb, c http://deepgreen.stanford.edu/ Images and movies of GFP-tagged proteins in various organelles in Arabidopsis thaliana GFP localisome databased http://www.psb.ugent.be/papers/cellbiol/ Images of GFP-tagged proteins involved in cytokinesis and cell plate formation in Arabidopsis thaliana and BY-2 cells GFP databasee http://data.jic.bbsrc.ac.uk/cgi-bin/gfp/ Images of GFP-tagged proteins in various organelles in Arabidopsis thaliana PODB2f http://podb.nibb.ac.jp/Organellome/ Images and movies of various visualized organelles at differet stages in several plant species SUBA IIg http://www.plantenergy.uwa.edu.au/applications/suba/index.php Images of GFP-tagged proteins in various organelles in Arabidopsis thaliana The Illuminated Plant Cellh http://www.illuminatedcell.com/ aBrown Images and movies of various visualized organelles in several plant species et al. (2005); bCutler et al. (2000); cLi et al. (2006); dDamme et al. (2004); eKoroleva et al. (2005); fMano et al. (2008); gHeazlewood et al. (2007); hMathur (2007). division and fusion. Live-cell imaging data are deposited as movie files, which offer valuable information that is not extractable from static image data. For example, peroxisomes are visualized by electron microscopy exclusively (Nishimura et al. 1986), because, unlike mitochondria, there is no specific dye for these organelles and because, unlike chloroplasts, peroxisomes are not autofluorescent. Peroxisomes were recognized as motile organelles that move dynamically in cells, until real-time imaging using GFP was applied to their analysis (Supplementary Movie 1; Jedd and Chua 2002, Mano et al. 2002, Mathur et al. 2002). Similar live-cell imaging approaches are applied to other plant organelles; therefore, the number of reports containing movie data as supplementary data continues to grow steadily. For example, the Plant Organelles Database 2 (PODB2) collects movie data that show the dynamic movement of various organelles (Fig. 1B, Supplementary Movie 1). In addition, as shown in Supplementary Movie 2 for the ER network in tobacco suspension-cultured cells (Mitsuhashi et al. 2000), movies for the rotation of 3D structures, which are constructed from serial images derived from different focal planes, enable a clear understanding of the stereological arrangement of organelles. This type of movie favors the elucidation of the spatial structure of the ER in a cell. Recently, many individual researchers have set up websites to upload their movie data. Regarding protein localization, some databases provide prediction information of protein localization based on amino acid sequences, such as plastids (Cui et al. 2006, O’Brien et al. 2009), mitochondria (Heazlewood et al. 2004, O’Brien et al. 2009) and peroxisomes (Reumann et al. 2004). Although this information is valuable as a starting point, often the localization information obtained in this way needs to be validated experimentally (flowchart in black in Fig. 3). In such cases, searches of image databases can be a powerful tool to confirm localization (flowchart in red in Fig. 3). Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. 2003 S. Mano et al. Image databases for plant organelle research Compared with text-based databases, there are few image databases for plant organelle research (Table 2). The Arabidopsis Nucleolar Protein Database (AtNoPDB) provides information on >200 proteins identified via a proteomic analysis using localization images of full-length cDNA–GFP fusions (Fig. 4A; Brown et al. 2005). The localization of each fusion protein is categorized into five different subnucleolar categories, based on localization image data: nucleolar, nucleolus-associated structures, nucleoplasmic, nuclear bodies and extranuclear (Brown et al. 2005). The GFP localisome database is dedicated to proteins that are implicated in cytokinesis and division-plane determination (Fig. 4B; Damme et al. 2004). The images of GFP fusion proteins were obtained from Arabidopsis thaliana and tobacco suspension-cultured cells at different developmental stages. These two databases allow the investigation of the nature of proteins localized at the nucleus and of cell-plate determination during cytokinesis. The project aimed at generating pools of independent transgenic A. thaliana expressing GFP-fused full-length cDNAs has been launched and the localization of each fusion gene product was determined in thousands of transgenic plants. Image data were deposited into the Fluorescent Tagging of Full-length Proteins database (FTFLPdb), which is open to the public (Fig. 4C; Cutler et al. 2000, Li et al. 2006). Additional image and movie data for organelle dynamics are uploaded on the website of Dr Ehrhardt (http://deepgreen .stanford.edu/), who is in charge of the construction of the FTFLPdb. The use of the FTFLPdb is a fast, first-level method to examine the localization of proteins of interest. Furthermore, resources such as transgenic seeds are distributed through the Arabidopsis Biological Resource Center (http://www.arabidopsis.org/). The GFP database at the John Innes Centre also provides information on the localization of Arabidopsis proteins (Fig. 4D; Koroleva et al. 2005). In this project, Arabidopsis full-length cDNAs fused to GFP were transiently expressed in Arabidopsis suspension-cultured cells for acquisition of image data. At present, 155 image data are collected in this database. The localization of each fusion protein is categorized into five main categories, based on localization image data: cytoplasm, nucleus, nucleolus, organelles and endomembrane compartments. Fig. 1 Examples of submitted image and movie data in the PODB2. (A) The thumbnails showing each image were downloaded from the database and arranged. The PODB2 houses data of various visualized 2004 organelles in different tissues and developmental stages in several plant species (Mano et al. 2008). (B) Output from the Organelles Movie Database in the PODB2 is shown. The movie represents behavior of the ER in the process of cell plate formation during cytokinesis in tobacco suspension-cultured cells. Green signal (i.e., GFP) allows the visualization of the ER. The red signal represents the endosome, which forms the cell plate and is visualized using FM4-64 (Higaki et al. 2008). Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. Image databases for plant organelle research Fig. 2 Morphology of visualized organelles in transgenic A. thaliana expressing a GFP fusion gene. Leaf (A–E, G–J, L) or root cells (F, K) of 12-dayold seedlings were observed using confocal scanning microscopy. (A) Cytosolic fluorescence from GFP without an organelle targeting signal (Mano et al. 2002). (B) Peroxisomes in the GFP–PTS1 plant (Mano et al. 2002). (C) Chloroplasts in the A5-3 plant expressing pt–sGFP (Niwa et al. 1999). (D) Mitochondria in the Mt–GFP plant (Arimura and Tsutsumi 2002). (E) ER and ER bodies in the GFP-h plant expressing SP–GFP–HDEL (Matsushima et al. 2002). (F) Nucleus in transgenic A. thaliana expressing GFP–puSRp35 (Mano et al. unpublished result). (G) Plasma membrane in transgenic A. thaliana (stock no. CS84725) that was donated to TAIR (Cutler et al. 2000). (H) Actin filaments in the GFP–hTalin plant (Takemoto et al. 2003). (I) Chloroplasts (red) and peroxisomes (green) from the GFP–PTS1 plant (Mano et al. 2002). (J) Tubulin in the GFP–TUA6 plant (Ueda et al. 1999). (K) Vacuoles in transgenic Arabidopsis thaliana expressing SP–GFP–2SC (Tamura et al. 2005). (L) Tonoplast in transgenic A. thaliana expressing gTIP–GFP (Mitsuhashi et al. 2000). Bars, 20 µm. Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. 2005 S. Mano et al. Fig. 3 Scheme for the application of image database to plant organelle research and systems biology. Flowchart in black: Genome and proteome databases provide prediction information of protein localization based on amino acid sequences. Image experiments can be performed to validate the prediction, and their results can be deposited in image databases. Flowchart in red: The data in the image databases, which were derived from imaging experiments, supplement the information in the genome and proteome databases. Flowchart in green: The image and movie data in the databases represent valuable and significant resources to obtain biologically meaningful information. Based on information extracted using image-based quantification, researchers can estimate the number of organelles in a cell, the size of each organelle, their spatial distribution, track motile organelles, etc. In addition, based on calculated results, researchers can compare their data with deposited data. Flowchart in blue: Data mining based on image-based quantification provides the basis for mathematical modeling, and imaging can also be a suitable method to verify the model. Flowchart in open arrows: The large amount of data deposited into various kinds of database must be used to identify and quantify the various components of organelles, cells, organs and individuals in systems biology. Image databases dedicated to protein localization and/or organelles are expected to advance for systems biology. 2006 Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. Image databases for plant organelle research Fig. 4 Web interfaces of some image databases. (A–E) Examples of a result screen for AtNoPDB (A, Brown et al. 2005), GFP localisome database (B, Damme et al. 2004), FTFLPdb (C, Cutler et al. 2000, Li et al. 2006), GFP database (D, Koroleva et al. 2005) and PODB2 (E, Mano et al. 2008). (F) The main page of the project of ‘The Illuminated Plant Cell’ (Mathur 2007). Figure details. A: Reproduced/ Brown, J.W.S., Shaw, P. and Marshall, D. F. (2005) Arabidopsis nucleolar protein database (AtNoPDB) Nucleic Acids Res. 33: D633–D636 with permission from Plant Bioinformatics group, Scottish Crop Research Institute. B: Reproduced/ Vam Damme, D., Bouget, F.Y., Vam Poucke, K., Inzé D. and Geelen, D. (2004) Molecular dissection of plant cytokinesis and phragmoplast structure: a survey of GFP-tagged proteins. Plant J. 40: 386–398. with permission from Vam Damme et al. C: Reproduced/ Li S, Ehrhardt DW, Rhee Sy. (2006) Systematic analysis of Arabidopsis organelles and a protein localisation database for facilitating flourescent tagging off full-length Arabidopsis proteins. Plant Physiol. 141(2):527–39. with permission from SY Rhee D: Reproduced/ Koroleva, O.A., Tomlinson, M.L., Leader, D., Shaw, P. and Doonan, J.H. (2005) High-throughput protein localization in Arabidopsis using Agrobacterium-mediated transient expression of GFP-ORF fusions. Plant J. 41: 162–174. with permission from Wiley- Blackwell Ltd. F: Reproduced/ Mathur J. (2007) The illuminated plant cell. Trends Plant Sci. 12: 506–513. with permission from Dr Jaideep Mathur. The subcellular location database for Arabidopsis proteins (SUBA), which was updated to version 2, houses large-scale proteomic and GFP localization data sets from various cellular compartments of A. thaliana (Heazlewood et al. 2007). This database collects information on protein localization based on proteomic surveys and literature references from other resources, such as TAIR and Swiss-Prot annotations. Therefore, compared with the FTFLPdb and the GFP database, in its current configuration, SUBA II places more weight on text-based information than on imagebased information. An increase in image data will be expected in the future. Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. 2007 S. Mano et al. The PODB2 houses data of various visualized organelles in different tissues and developmental stages in several plant species (Figs. 1, 4E; Mano et al. 2008). Unlike the five databases described above, which are compilations of localization data of GFP fusion gene products, the PODB2 focuses on organelle dynamics rather than on the localization of each gene product. Therefore, even for the same organelle, this database collects several images that were acquired under various conditions. For example, the PODB2 provides a series of images of changes in actin filaments throughout the progression of the cell cycle in suspension-cultured tobacco cells, as well as of the positions of chloroplasts in Arabidopsis mesophyll cells in response to changes in light conditions. The comparison of images from various conditions allowed the discovery that actin filaments drastically change in shape, length, thickness, number and position during the cell cycle and that chloroplasts move away from the cell surface to avoid photodamage from strong light. The unique feature of the PODB2 is that it has been populated by data determined experimentally and submitted directly by plant researchers. In addition, the databases described above collect image data mainly for A. thaliana, whereas the PODB2 deals with images stemming from any plant species. Therefore, the comparison of images showing the same organelles among different plant species is available via the PODB2. In 2008, this database was updated to deal with movie data, such as time-lapse imaging and the rotation of 3D structures. Therefore, investigators can examine more easily dynamic changes in organelles, such as movement, division and their spatial arrangement in cells (Fig. 1B, Supplementary Movies 1, 2). In addition to the databases described above, a wealth of image data on plant organelles is uploaded onto the websites of individual laboratories. Although these are not largescale data, visitors can obtain valuable information (such as sophisticated protocols for image detection) and view image data. For example, the website of ‘The Illuminated Plant Cell’ provides not only image and movie data for several organelles, but also additional information, including the collection of vectors used for the visualization of organelles (Fig. 4F; Mathur 2007). Similarly to the PODB2, the data deposited in this website are composed of results determined experimentally by the contributors. The potential of image databases as resources for plant organelle research Platforms as search tools for unidentified subcellular structures Visualization of organelles sometimes leads to the discovery of new subcellular structures. The stromule (stroma-filled tubules) (Köhler et al. 1997) and the ER body (Matsushima 2008 et al. 2002) are good examples of subcellular structures that were identified using visualization with GFP in living cells. Stromules are motile, thin protrusions that emanate from the plastid surface into the cytosol via the expression of GFP targeted to the plastid stroma in tobacco and petunia cells (Köhler et al. 1997). Analyses using fluorescence recovery after photobleaching (FRAP) and GFP-tagged plastid proteins revealed that stromules have the capacity to form a link between individual plastids and exchange macromolecules (Kwok and Hanson 2004). ER bodies were originally described as mystery organelles that were derived from plastids (Gunning 1998); however, the morphology of the unidentified GFP-labeled structures triggered their identification as ER bodies (Hayashi et al. 2001). The deposition of a significant amount of additional visualized subcellular structure data into image databases is expected to render them useful platforms for the comparison of unidentified organelles with the deposited image data (flowchart in green in Fig. 3). As new subcellular structures, such as Rubisco-containing bodies (Ishida et al. 2008) and secretory vesicle clusters (Toyooka et al. 2009), were found via visualization with GFP, the image-based comparison through image databases will allow investigators to shorten the time-consuming work of searching for references relevant to unidentified subcellular structures. Quantification analysis based on image data The image and movie data collected in the databases represent valuable and significant resources to obtain biologically meaningful information, as image data provide a wealth of information on size, length and morphology. Additionally, information on the velocity and direction of organelles can be estimated using time-lapse data. In addition, the 3D structures constructed from serial images from different focal planes convey the spatial information of visualized organelles in cells. In other words, quantification based on image data yields a statistical power that allows changes in organelle dynamics to be shown. Based on information extracted using image-based quantification, researchers can estimate the number of organelles in a cell, the size of each organelle, their spatial distribution and track motile organelles, etc. (flowchart in green in Fig. 3). The quantification of image data comprises several steps, which include segmentation (which outlines and identifies particular regions in an image), edge detection of segmented regions, calculation of each region and registration, which aligns calculated images. The process of tracking objects is included in the analyses of movie data. Each step is affected by several factors, especially by the resolution of data. Although slow scanning and/or application of averaging techniques generates high-resolution data for enhanced identification of the objects, these approaches may cause photobleaching and objects such as proteins and organelles Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. Image databases for plant organelle research may disappear from the focal plane. In contrast, the reduction of scanning time may cause poor resolution. Therefore, the duration of the scanning time depends on the intensity of the visualized object and the velocity of movement of targets. Recent instrument developments produced new microscopes and cameras that can be used to obtain high resolution and/or fast shutter speeds. Furthermore, new fluorescent proteins were exploited that exhibit higher fluorescence intensity. These new technologies and tools will assist the quantification aspect of image analysis. A good overview of quantification of image data is provided by Hamilton (2009). Unfortunately, at present there are no general protocols for image-based quantification that cover all image data, although computational analytical tools are techniques that are increasingly indispensable for these analyses. The REANTlight software is suitable for reconstitution of 3D structures of organelles from serial optical sections, and the volume and surface areas of protoplasts and vacuoles were measured using this software (Kutsuna and Hasezawa 2005). Recently, this software was applied to the reconstruction of the 3D structure of the plasma membrane in root hair cells, using plasma-localized soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE), SYP123 (Enami et al. 2009). These results revealed the general-purpose use of this software for several organelles. The ‘Organelle View’ device of the Organelle DB (Wiwatwattana et al. 2007), which is derived mainly from yeast data at present, allows the animation of rotation in the window to show views from different angles (Wiwatwattana et al. 2007). These systems are excellent as visual aids for quantification and representation. Some imaging analysis applications are incorporated into the microscope system (Fig. 5A). In addition, various commercial applications, such as Metamorph (Fig. 5B; http:// www.moleculardevices.com/pages/software/metamorph .html), Imaris (http://www.bitplane.com/) and Volocity (http://www.improvision.com/) are now available. In addition, other analytical tools for the processing of image data, such as ImageJ and Profiler (Carpenter et al. 2006), are also available as open sources (Table 3). In particular, ImageJ is widely used for image analysis (Fig. 5C, D), as it is a free downloadable application and many plug-ins and macros (which enable users to perform new methods easily) have been developed and distributed via their respective websites. Therefore, these open sources provide a common foundation for the sharing of methods, tools and information regarding image analysis. In addition, several protocols, applications and tips for image analysis are provided through the websites of individual laboratories, such as Dr Hasezawa’s laboratory (http://hasezawa.ib.k.u-tokyo.ac .jp/zp/hlab), Dr Haseloff’s laboratory (http://www.plantsci .cam.ac.uk/Haseloff/index.htm) and Dr Hawe’s laboratory (http://www.brookes.ac.uk/lifesci/research/molcell/hawes/ gfp.htm!). Table 3 A selection of open source application tools for image analysis Name URL BioImage Suite http://www.bioimagesuite.org/ BISQUEa http://www.bioimage.ucsb.edu/ CellProfiler http://www.cellprofiler.org/index.htm CellTracker http://dbkgroup.org/celltracker/index.php Cold Spring Harbor Protocols http://cshprotocols.cshlp.org/ iCluster http://icluster.imb.uq.edu.au/ ImageJ http://rsb.info.nih.gov/ij/ ImageSurfer http://cismm.cs.unc.edu/downloads/ MayaVi Data Visualizer http://mayavi.sourceforge.net/ MSIb http://www.molsci.org/about/index.html OMEc http://www.openmicroscopy.org/site Paraview http://www.paraview.org/ SCMDd http://scmd.gi.k.u-tokyo.ac.jp/datamine/ aBISQUE: Bisque - Bio-Image Semantic Query User Environment; bMSI: Molecular Sciences Institute; cOME: Open Microscopy Environment; dSCMD: Saccharomyces Cerevisiae Morphological Database. Image databases as resources for systems biology Systems biology is a comprehensive study of the dynamics and structure of complete biological systems. The achievement of this aim requires the integration of information on a large numbers of elements, which include entities such as genes, proteins, organelles, metabolites, etc. Therefore, various data deposited into databases, which were generated using several ‘omics’ approaches, are used to extract hidden patterns, interactions and mechanisms that underlie biological processes (flowchart in open arrows in Fig. 3). For example, the interaction of carbon with nitrogen or carbon with light in A. thaliana were systematically addressed and qualitative multinetwork models were constructed (Gutiérrez et al. 2007, Thum et al. 2008). Moreover, metabolomics data were integrated with the data from pathway and co-expression databases to investigate the metabolite correlation networks (Kusano et al. 2007). As described above, image and movie data contain valuable biological information on protein and organelle dynamics. Therefore, image databases dedicated to protein localization and/or organelles contribute to systems biology as potentially rich data sources to investigate the behavior and localization of gene products and the behavior of the organelles that house these proteins. For example, the fluorescence pattern of the GFP–PIN1 fusion protein is used as a computed-simulation model of phyllotaxis via auxintransport-mediated patterning of the developing meristem (Berleth et al. 2007). As stated above, the reconstitution of the vacuolar membrane at different stages of tobacco Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. 2009 S. Mano et al. Fig. 5 Application of computational analytical tools in image analysis. (A) The fusion of GFP with one peroxisomal membrane protein was transiently expressed in onion cells with red fluorescent protein (RFP)–PTS1, which was a peroxisomal matrix marker. The intensity of both GFP and RFP signals in red line, which is shown in image data, were analyzed using the LSM5 software version 3.2 (Carl Zeiss, Jena, Germany). (B) GFP fluorescence of root cells in transgenic A. thaliana expressing GFP without any targeting signals were observed, and the intensity of signals was calculated and visualized with pseudocolors by MetaMorph (Nihon Molecular Devices, Tokyo, Japan). (C) The image of peroxisomes visualized by GFP in leaf cells of an A. thaliana peroxisome biogenesis mutant that shows various sizes of peroxisome was acquired using CLSM. Edge detection of peroxisome was implemented in ImageJ. (D) The number, area, intensity and circularity of each peroxiosme in (C) were calculated. 2010 Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. Image databases for plant organelle research suspension-cultured cells (Kutsuna and Hasezawa 2005) and of the plasma membrane in Arabidopsis root hair cells (Enami et al. 2009) was performed based on image data of GFP fusion proteins. The addition of additional data, such as expression data, proteomics data, and interactome data, to these results will extend our knowledge at the subcellular and cellular levels. The metabolic network of primary metabolisms in Chlamydomonas reinhardtii was reconstructed using genomic and biochemical information (Boyle and Morgan 2009). In this analysis, the subcellular localization of metabolic enzymes is considered, albeit based on the prediction program. To extract information on protein–protein interactions in mammalian and yeast cells, the subcellular localization of proteins was evaluated using several databases (mainly text-based databases) (Shin et al. 2009). If the information in image databases is incorporated into the analyses for prediction of subcellular localization, the reconstruction of networks or simulation models will become more confirmatory and will refine our understanding of biological systems. As the PODB2 contains image and movie data of proteins and organelles at different stages and in the presence/absence of environmental stimuli, such as light (Mano et al. 2008), this database has the potential to play an important role, as it verifies simulation models and provides information on the reconstruction of simulation models (flowchart in blue in Fig. 3). In the UK, the Centre for Plant Integrative Biology (CPIB) at the University of Nottingham aims to create a virtual root as an example of the use of integrative systems biology to model multicellular systems (http://www.cpib.info/). To accomplish this purpose, imaging approaches are incorporated with experimental, innovative mathematical, engineering and computer science research. In the USA, the ‘iPlant Collaborative’ project was launched to give plant scientists new conceptual advances through integrative and computational thinking via the construction of cyberinfrastructures, which consist of a comprehensive combination of hardware, software, statistical measurements, data mining, modeling and simulation, and bioinformatics (Ledford 2009, http://www.iplantcollaborative.org/). Image analyses at the subcellular, cellular and individual levels are proposed as morphodynamics research projects in this ‘iPlant Collaborative’ project. These image analyses include acquisition of image data, the development of modeling software and the incorporation of the systems developed into image databases. Thus, image databases will continue to be important for the enhancement of systems biology. The several imaging techniques available and their utility in systems biology are reviewed by Kherlopian et al. (2008). Notes on handling image database We should keep in mind that image techniques have their limitations, as do all technologies. Therefore, we should be careful in dealing with image data regarding the accuracy of the data. For example, the expression of GFP fusion genes in cells or application of dyes has the potential to generate experimental artifacts. Investigators may have to examine individually whether deposited data are evaluated for sufficient quality using appropriate measurements. In the case of protein localization, besides imaging data (such as double staining of organellar proteins with a predetermined localization), other approaches such as biochemical analysis and complementation of mutant phenotypes would be convincing. The validation of the localization of fluorescent protein fusions is reviewed extensively by Moore and Murphy (2009), and Millar et al. (2009). Image data provide quantitative and semi-quantitative insights into plant organelle research. To gain detailed information based on image data, one needs tools with finer resolution by confocal laser scanning microscope (CLSM). In this case, the intensity of fluorescent and/or non-fluorescent probes in cells are affected by various factors, such as gene expression, permeability of dyes and transport efficiency of gene products. Although it is instructive to keep the limitations of imaging analyses in mind when drawing conclusions about cellular events based on this type of analysis, image databases have the potential to take advantage of direct comparison of control and experimentally manipulated cells to determine whether the different image is true or false (e.g., sampling error). However, the careful application of imaging approaches to other techniques, such as genetic and biochemical studies, and their integration will allow the demonstration of the significant impact of imaging technology on plant organelle dynamics. Image databases as resources for educational use The image databases may serve as an educational aid that engages both biology students and members of the general public who are interested in biology, via a visually ‘fun’ interface. In addition to image databases for plant organelles, different image databases provide image data information, such as individual organisms, including plants. For example, ImageBank (http://bio.ltsn.ac.uk/imagebank/) contains image data for various organisms (including plant species). The Plants Database (http://plants.usda.gov/) and the Protist Information Server (http://protist.i.hosei.ac.jp/) are dedicated to the collection of image and movie data from various plant species and protists, respectively. In most cases, images may only be freely downloaded and used for educational purposes, such as learning and teaching. It is, therefore, expected that image databases will be easily accessible platforms and will accelerate the interest of younger generations in plant biology. Finally, we should acknowledge the contributor and the copyright holder of the images and movies from the public database every time these are used. Accurate credit leads to improvement of the status and better management of databases. Plant Cell Physiol. 50(12): 2000–2014 (2009) doi:10.1093/pcp/pcp128 © The Author 2009. 2011 S. Mano et al. Conclusions and prospects Direct visual analysis is a persuasive approach—imaging techniques have been the ‘eyes’ of science. The development of imaging techniques in the field of plant organelle research expands our current insights and contributes to the solidification of old concepts and the replacement of others with new concepts. In the past, several approaches, such as electron microscopy, provided some snapshot (or steady-state) information on organelles, but not organelle dynamics, such as movement, division and fission. Now that almost all plant organelles are easily visualized and their dynamics are investigated in living cells, knowledge of plant organelle dynamics has been accumulating at a rapid pace in the form of image data. Additionally, the equipment for acquisition of images has evolved and is now applied to other fields. For example, microscale magnetic resonance imaging (MRI), which is mainly used for clinical imaging, was used to acquire images of chloroplasts in Spirogyra alga and the reconstructed 3D view displayed the spiral-shaped array of chloroplasts on the inner surface of the cell wall (Ciobanu and Pennington 2004). To use these image data as valuable resources, the infrastructure of image databases will be improved by including exploitation of better languages of data representation and visualization, improvement of common platforms with other databases and development of computational analytical tools. Computational biologists, mathematicians and software engineers will play an active part in this field. Although the utilization of image databases as resources for systems biology is still very much a developing research area, new methodologies are currently being developed and tested. The increase in image data available and the use of image databases will open new perspectives in all fields of plant biology, including plant organelle dynamics. Image databases will be as valuable as those of infrastructures. Supplementary data Supplementary data are available at PCP Online. Funding The Ministry of Education, Sports, Culture, Science, and Technology, the Grant-in-Aid for Scientific Research of Priority Areas ‘Organelle Differentiation as the Strategy for Environmental Adaptation in Plants’ (No. 16085101); the Japan Society for the Promotion of Science Grant-in-Aid for Publication of Scientific Research Results (No. 218060). Acknowledgments We are grateful to Drs Shin-ichi Arimura from the University of Tokyo, Hirokazu Kobayashi from the University of Shizuoka, Ikuko Hara-Nishimura from Kyoto University, 2012 Yasuo Niwa from the University of Shizuoka, Takashi Hashimoto from the Nara Institute of Science and Technology, and Daigo Takemoto from Nagoya University for kindly providing seeds of transgenic A. thaliana. We would like to thank Ms Yuko Kuboki and Chizuru Ueda from the Department of Cell Biology and the staff at the Strategic Planning Department of the National Institute for Basic Biology for their assistance in English proofreading and for maintaining the PODB2 website. References Arimura, S. and Tsutsumi, N. (2002) A dynamin-like protein (ADL2b), rather than FtsZ, is involved in Arabidopsis mitochondrial division. Proc. Natl Acad. Sci. USA 99: 5727–5731. Berg, R.H. and Beachy, R.N. (2008) Fluorescent protein application in plants. Methods Cell Biol. 85: 153–177. 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