Special Issue: Plant Cell Biology   

August 2007, Volume 49 Issue 8, Pages 1089-1278.

Cover Caption:
Plant morphogenesis is driven by microtubules at the cellular level
In the elongated cells, which have entered a vegetative pathway leading to highly specialized elaters, microtubules are becoming stabilized into spiral bands, In the spherical cells, which are in the reproductive lineage leading to spore production, microtubules are driving the complex and highly dynamic process of meiosis. See pages 1142-1153 for details.


Celebrating Plant Cells: A Special Issue on Plant Cell Biology  
Author: Zhenbiao Yang and Bo Liu
Journal of Integrative Plant Biology 2007 49(8): 1089-1090
DOI: 10.1111/j.1672-9072.2007.00525.x
    A special issue on plant cell biology is long overdue for JIPB! In the last two decades or so, the plant biology community has been thrilled by explosive discoveries regarding the molecular and genetic basis of plant growth, development, and responses to the environment, largely owing to recent maturation of model systems like Arabidopsis thaliana and the rice Oryza sativa, as well as the rapid development of high throughput technologies associated with genomics and proteomics. However, major gaps remain in our mechanistic understanding of plant processes, especially regarding how a gene or a network of genes spatially and temporally regulates a particular developmental process or a physiological response at the cellular level.Because cells are the most fundamental functional units among living organisms, we won°Įt understand how and why a plant process is operated until we reveal how cellular activities integrate genes, molecules, and environmental cues for developmental and physiological processes at the tissue, organ and whole plant levels. For example, we now know all the genes in the Arabidopsis genome that are regulated by auxin, and how auxin is perceived by the nuclear signaling pathway leading to the changes in the expression of these genes. For the most part, however, we do not know how these genes modulate cell division, polarized growth, and differentiation. Neither do we know how the perception of auxin results in cytoplasmic events, such as the dynamic remodeling of the cytoskeleton, that clearly contribute to auxin-regulated cellular processes. As the first step in bridging the knowledge gaps in plant biology, it is imperative to elucidate the genetic and molecular mechanisms underlying fundamental cellular processes (e.g. biogenesis and dynamics of subcellular compartments or organelles, cytoskeletal organization and dynamics, and cell wall biogenesis and remodeling) and cellular behaviors (e.g. cell growth, cell division, morphogenesis, polarity establishment, differentiation, and cell-to-cell communication). Studies on these fundamental topics using plant cells as model systems as well as on unique cellular structures (chloroplast, plasmodesmata, cell wall) and processes in plants also contribute to our knowledge of how living cells function in general. Research in cell biology has been greatly aided by rapid advances in technologies like modern laser scanning and spinning disk confocal microscopy and live-cell imaging technologies, as well as improved transmission electron microscopy, which have opened new windows to visualizing and analyzing molecular dynamics in real time and the ultrastructural details of subcellular compartments. When applied to integrate the genetic and genomic in model plant systems such as Arabidopsis, these sophisticated technologies become particularly powerful. Consequently, in recent years we have witnessed exciting and important advances in plant cell biology. In this special issue, we feature a series of review articles from experts, which have highlighted and analyzed recent progress in important topics of plant cell biology, as well as a number of selective original research articles. We have intended to cover broad aspects of plant cell biology with regards to the broad readership of JIPB. The classical topics on the biogenesis,dynamics and function of subcellular compartments (organelles) are experiencing a new life, as relevant new functions are being discovered and the molecular and genetic basis of these processes are being revealed. Faithful sample preservation procedures combined with the high resolution electron tomography technique have opened our eyes to unprecedented details of 3-D subcellular structures (Haas and Otegui). Recent studies have uncovered important roles of chloroplast outer membranes in protein translocation and regulation of metabolic activities and signaling processes (Inoue). Genetic studies have generated new insights into the molecular mechanism underlying the multiplication of the plant peroxisome (Hu). Through serendipitous biochemical and microscopic analysis, molecular identities of provacuolar compartments and endosomal compartments are surfacing (Lam et al.). Members of the conserved RAB guanosine triphosphatase (GTPase) family function as key regulators in vesicular trafficking in the secretory and endocytic pathways. Genomic or bioinformatic analyses not only implicate the functional conservation of RABGTPases, but also pinpoint their specialization in plant processes (Zhang et al.). The cytoskeleton is arguably one of the most actively pursued subjects in plant cell biology, reflecting its paramount importance not only in structural regulation but also in signaling processes of growth, development, and responses to the environment. Consequently, it attracts particular attention in this special issue. Because of the lack of a structurally defined microtubule-organizing center (MTOC), such as the spindle pole body in fungi and the centrosome in animals, unique features of plant microtubule organization demonstrated by various plant cells have intrigued plant cell biologists for many decades. The ¶√-tubulin complex functions as the microtubule nucleator among eukaryotic organisms. A detailed phylogenetic analysis has indicated that subunits of this complex are well conserved among land plants (Murata). Intriguing MTOC structures are demonstrated by various land plants, especially in bryophytes, which lead to a concept of pleiomorphic and migratory MTOC from an evolutionary perspective (Brown and Lemmon; Brown et al.). The cortical microtubule array directly influences cell morphogenesis and consequently plant development, which has probably received the most scrutiny in the field of the plant cytoskeleton. The dynamic behavior of cortical microtubules is regulated by a large number of diverse microtubule-associated proteins, known as MAPs, including those conserved ones and those unique to plants (Kaloriti et al.; Burk et al.; Zhou et al.). Increasing evidence shows the importance of actin microfilaments in plant growth and development. Isolation and characterization of actin-binding proteins begin to unravel molecular mechanisms that regulate actin organization and dynamics for cellular activities (Su et al.). The cytoskeleton is the muscle for cell polarity establishment, a fundamental process crucial for morphogenesis and cell differentiation. Fucoid algae provide their elegant zygotes for us to visualize the integrated activities of actin microfilaments and microtubules during cell polarization and asymmetric cell division (Bisgrove). Apart from cell morphogenesis, cell polarity, and cell differentiation, cell cycle control is another important aspect of cell behaviors that is intimately related to growth and development. The cell cycle is regulated by developmental signals, hormones and environmental cues, but much is to be learned about the how question. An in silico study identifies novel cell cycle regulators,and may ultimately help us understand complex mechanisms of the cell cycle exhibited by plants (Wang and Yang). Meiosis remains to be a fascinating topic for plant cell biologists. Molecular genetic studies in Arabidopsis have contributed to our basic understanding of the molecular mechanism for meiotic recombination in plants, a fundamental process for inheritance and generation of genetic diversity (Wijeratne and Ma). Besides mysteries about the cell cycle machinery itself, an accompanying question of how organelles are properly partitioned into two daughter cells has always attracted cell biologists°Į attentions (Sheahan et al.). The pollen tube communicates intimately with female tissues to render both compatible and self-incompatible interactions.Pollen tubes cultured in vitro provide an exciting system for the investigation of cell-to-cell communication and cellular signaling in plants, especially on signal-mediated cellular activities such as cytoskeletal dynamics, exocytosis, and cell death. Important and exciting progress has been made in self-incompatible reaction-mediated cellular signaling in pollen tubes (Franklin-Tong).Pollen tubes display oscillation of the tip-focused cytosolic calcium gradient that is required for pollen tube growth, which seems to depend on channel-mediated calcium influx. A putative plasma membrane-localized calcium-permeable channel has been identified (Chang et al.). The cell wall provides a framework for cell shape determination, and for the integrity and physical strength of plants. As an integral effort in understanding the evolution of land plants, analysis of cell wall polysaccharides from a moss to advanced gymnosperms reveals both highly conserved and modified features (Nothnagel and Nothnagel). The cell wall°Įs role in cell-to-cell communication and signaling receives more and more attention. Plasmodesmata, a highly dynamic and regulated channel connecting the symplast and transporting small molecules, proteins and RNAs across plant cells, provide a unique mechanism for cell-to-cell communication in plants. Interestingly, plant viruses have hijacked the plasmodesmata transport machinery to allow them to spread throughout the plant body. Significant progress has been made in this fascinating subject of plant cell biology (Ding and Itaya). In spite of our desire to be as inclusive as possible in this special issue, we have inevitably missed many important subjects that are under intensive scrutiny, as demonstrated by the active research in all cylinders of plant cell biology. It is clear that the field of plant cell biology is breaking the dawn of our mechanistic understanding of cellular behaviors and their underlying linkage to genes and molecules. Ultimately, plants harness splendid cellular behaviors for their fascinating growth and developmental processes,and for their responses to the environment. It is our hope that this special issue shows the inheritance of a traditional emphasis in cell biology by Acta Botanica Sinica, and the commitment to reporting breakthroughs in nderstanding plant cells by the Journal of Integrative Plant Biology. More fascinating tales of plant cells are yet to be told!
Abstract (Browse 2959)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
          Invited Expert Reviews
Electron Tomography in Plant Cell Biology  
Author: Thomas J. Haas and Marisa S. Otegui
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00540.x
    This review focuses on the contribution of electron tomography-based techniques to our understanding of cellular processes in plant cells. Electron microscopy techniques have evolved to provide better three-dimensional resolution and improved preservation of the subcellular components. In particular, the combination of cryofixation/freeze substitution and electron tomography have allowed plant cell biologists to image organelles and macromolecular complexes in their native cellular context with unprecedented three-dimensional resolution (4®C7 nm). Until now, electron tomography has been applied in plant cell biology for the study of cytokinesis, Golgi structure and trafficking, formation of plant endosome/prevacuolar compartments, and organization of photosynthetic membranes. We discuss in this review the new insights that these tomographic studies have brought to the plant biology field.
Abstract (Browse 1741)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
The Chloroplast Outer Envelope Membrane: The Edge of Light and Excitement  
Author: Kentaro Inoue
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00543.x
    The chloroplast is surrounded by a double-membrane envelope at which proteins, ions, and numerous metabolites including nucleotides, amino acids, fatty acids, and carbohydrates are exchanged between the two aqueous phases, the cytoplasm and the chloroplast stroma. The chloroplast envelope is also the location where the biosynthesis and accumulation of various lipids take place. By contrast to the inner membrane, which contains a number of specific transporters and acts as the permeability barrier, the chloroplast outer membrane has often been considered a passive compartment derived from the phagosomal membrane. However, the presence of galactoglycerolipids and ¶¬-barrel membrane proteins support the common origin of the outer membranes of the chloroplast envelope and extant cyanobacteria. Furthermore, recent progress in the field underlines that the chloroplast outer envelope plays important roles not only for translocation of various molecules, but also for regulation of metabolic activities and signaling processes. The chloroplast outer envelope membrane offers various interesting and challenging questions that are relevant to the understanding of organelle biogenesis, plant growth and development, and also membrane biology in general.
Abstract (Browse 2772)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Plant Peroxisome Multiplication: Highly Regulated and Still Enigmatic  
Author: Jianping Hu
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00537.x
    Plant peroxisomes play a key role in numerous physiological processes and are able to adapt to environmental changes by altering their content, morphology, and abundance. Peroxisomes can multiply through elongation, constriction, and fission; this process requires the action of conserved, as well as species-specific proteins. Genetic and morphological analyses have been used with the model plant Arabidopsis thaliana to determine at the mechanistic level how plant peroxisomes increase their abundance. The five-member PEX11 family promotes early steps of peroxisome multiplication with an unknown mechanism and some subfamily specificities. The dynamin-related protein (DRP)3 subfamily of dynaminrelated large guanosine triphosphatases mediates late steps of both peroxisomal and mitochondrial multiplication. New genetic and biochemical tools will be needed to identify additional, especially plant-specific, constituents of the peroxisome multiplication pathways.
Abstract (Browse 1619)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Molecular Characterization of Plant Prevacuolar and Endosomal Compartments  
Author: Sheung Kwan Lam, Yu Chung Tse, Yansong Miao, Hong-Ye Li, Junqi Wang, Sze Wan Lo
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00517.x
    Prevacuolar compartments (PVCs) and endosomal compartments aremembrane-bound organellesmediating protein traffic to vacuoles in the secretory and endocytic pathways of plant cells. Over the years, great progress has been made towards our understanding in these two compartments in plant cells. In this review, we will summarize our contributions toward the identification and characterization of plant prevacuolar and endosomal compartments. Our studies will serve as important steps in future molecular characterization of PVC biogenesis and PVC-mediated protein trafficking in plant cells.
Abstract (Browse 1886)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Diversification of the RAB Guanosine Triphosphatase Family in Dicots and Monocots  
Author: Jiaming Zhang, Daniel R. Hill and Anne W. Sylvester
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00520.x
    RAB guanosine triphosphatases (GTPases) are key regulators of vesicle trafficking and are essential to the growth and development of all eukaryotic cells. During evolution, the RAB family has expanded in different patterns to facilitate distinct cellular, developmental and physiological adaptations. Yeast has only 11 family members, whereas mammalian RABs have expanded to 18 RAB subfamilies. Plant RABs have diversified primarily by duplicating members within a single subfamily. Plant RABs are divided into eight subfamilies, corresponding to mammalian RAB1, RAB2, RAB5, RAB6, RAB7, RAB8, RAB11 and RAB18. Functional diversification of these is exemplified by the RAB11s, orthologs of which are partitioned into unique cell compartments in plants where they function to transport vesicles during localized tip growth. Similarly, the RAB2 family in grasses is likely involved in vesicle secretion associated with wall expansion, as determined by analysis of over-expression mutants. We propose that dicots and monocots have also diverged in their RAB profiles to accommodate unique cellular functions between the two groups. Here we present a bioinformatics analysis comparing the RAB sub-families of rice, maize and Arabidopsis. These results will guide future functional studies to test for the role of diversification of subfamilies unique to monocots compared to dicots.
Abstract (Browse 2734)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
The Pleiomorphic Plant MTOC: An Evolutionary Perspective  
Author: Roy C. Brown and Betty E. Lemmon
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00538.x
    ¶√-Tubulin is an essential component of the microtubule organizing center (MTOC) responsible for nucleating microtubules in both plants and animals. Whereas ¶√-tubulin is tightly associated with centrosomes that are inheritable organelles in cells of animals and most algae, it appears at different times and places to organize the myriad specialized microtubule systems that characterize plant cells. We have traced the distribution of ¶√-tubulin through the cell cycle in representative land plants (embryophytes) and herein present data that have led to a concept of the pleiomorphic and migratory MTOC. The many forms of the plant MTOC at spindle organization constitute pleiomorphism, and stage-specific °įmigration°Ī is suggested by the consistent pattern of redistribution of ¶√-tubulin during mitosis. Mitotic spindles may be organized at centriolar centrosomes (only in final divisions of spermatogenesis), polar organizers (POs), plastid MTOCs, or nuclear envelope MTOCs (NE-MTOCs). In all cases, with the possible exception of centrosomes in spermatogenesis, the ¶√-tubulin migrates to broad polar regions and along the spindle fibers, even when it is initially a discrete polar entity. At anaphase it moves poleward, and subsequently migrates from polar regions (distal nuclear surfaces) into the interzone (proximal nuclear surfaces) where interzonal microtubule arrays and phragmoplasts are organized. Following cytokinesis, ¶√-tubulin becomes associated with nuclear envelopes and organizes radial microtubule systems (RMSs). These may exist only briefly, before establishment of hoop-like cortical arrays in vegetative tissues, or they may be characteristic of interphase in syncytial systems where they serve to organize the common cytoplasm into nuclear cytoplasmic domains (NCDs).
Abstract (Browse 1986)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
How do Plants Organize Microtubules Without a Centrosome?  
Author: Takashi Murata, Takako Tanahashi, Tomoaki Nishiyama, Kazuo Yamaguchi and Mitsuyasu Hasebe
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00545.x
    A microtubule nucleates from a ¶√-tubulin complex, which consists of ¶√-tubulin, proteins from the SPC97/SPC98 family, and the WD40 motif protein GCP-WD. We analyzed the phylogenetic relationships of the genes encoding these proteins and found that the components of this complex are widely conserved among land plants and other eukaryotes. By contrast, the interphase and mitotic arrays of microtubules in land plants differ from those in other eukaryotes. In the interphase cortical array, the majority of microtubules nucleate on existing microtubules in the absence of conspicuous microtubule organizing centers (MTOCs), such as a centrosome. During mitosis, the spindle also forms in the absence of conspicuous MTOCs. Both poles of the spindle are broad, and branched structures of microtubules called microtubule converging centers form at the poles. In this review, we hypothesize that the microtubule converging centers form via microtubuledependent microtubule nucleation, as in the case of the interphase arrays. The evolutionary insights arising from the molecular basis of the diversity in microtubule organization are discussed.
Abstract (Browse 2634)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Microtubule Associated Proteins in Plants and the Processes They Manage  
Author: Despina Kaloriti, Charitha Galva, Chaithanyarani Parupalli, Noha Khalifa, Megan Galvin and John C. Sedbrook
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00541.x
    Microtubule associated proteins (MAPs) are proteins that physically bind to microtubules in eukaryotes. MAPs play important roles in regulating the polymerization and organization of microtubules and in using the ensuing microtubule arrays to carry out a variety of cellular functions. In plants, MAPs manage the construction, repositioning, and dismantling of four distinct microtubule arrays throughout the cell cycle. Three of these arrays, the cortical array, the preprophase band,and the phragmoplast, are prominent to plants and are responsible for facilitating cell wall deposition and modification,transducing signals, demarcating the plane of cell division, and forming the new cell plate during cytokinesis. This review highlights important aspects of how MAPs in plants establish and maintain microtubule arrays as well as regulate cell growth, cell division, and cellular responses to the environment.
Abstract (Browse 1752)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
The Katanin Microtubule Severing Protein in Plants  
Author: David H. Burk, Ruiqin Zhong and Zheng-Hua Ye
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00544.x
    Katanin is a heterodimeric microtubule (MT) severing protein that uses energy from ATP hydrolysis to generate internal breaks along MTs. Katanin p60, one of the two subunits, possesses ATPase and MT-binding/severing activities, and the p 80 subunit is responsible for targeting of katanin to certain subcellular locations. In animals, katanin plays an important role in the release of MTs from their nucleation sites in the centrosome. It is also involved in severing MTs into smaller fragments which can serve as templates for further polymerization to increase MT number during meiotic and mitotic spindle assembly. Katanin homologs are present in a wide variety of plant species. The Arabidopsis katanin homolog has been shown to possess ATP-dependent MT severing activity in vitro and exhibit a punctate localization pattern at the cell cortex and the perinuclear region. Disruption of katanin functions by geneticmutations causes a delay in the disappearance of the perinuclear MT array and results in an aberrant organization of cortical MTs in elongating cells. Consequently, katanin mutations lead to defects in cell elongation, cellulose microfibril deposition, and hormonal responses. Studies of katanin in plants provide new insights into our understanding of its roles in cellular functions.
Abstract (Browse 1806)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
The Villin/Gelsolin/Fragmin Superfamily Proteins in Plants  
Author: Hui Su, Ting Wang, Huaijian Dong and Haiyun Ren
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00546.x
    The villin/gelsolin/fragmin superfamily is a conserved Ca2+-dependent family of actin-regulating proteins that is widely present both in mammalian and non-mammalian organisms. They have traditionally been characterized by the same core of three or six tandem gelsolin subdomains. The study in vertebrates and lower eukaryotic cells has revealed that the villin/gelsolin/fragmin superfamily of proteins has versatile functions including severing, capping, nucleating or bundling actin filaments. In plants, encouraging progress has been made in this field of research in recent years. This review will summarize the identified plant homologs of villin/gelsolin/fragmin superfamily, thus providing a basis for reflection on their biochemical activities and functions in plants.
Abstract (Browse 2053)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Cytoskeleton and Early Development in Fucoid Algae  
Author: Sherryl R. Bisgrove
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00518.x
    Cell polarization and asymmetric cell divisions play important roles during development in many multicellular eukaryotes.Fucoid algae have a long history as models for studying early developmental processes, probably because of the ease with which zygotes can be observed and manipulated in the laboratory. This review discusses cell polarization and asymmetric cell divisions in fucoid algal zygotes with an emphasis on the roles played by the cytoskeleton.
Abstract (Browse 1488)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Genetic Analyses of Meiotic Recombination in Arabidopsis  
Author: Asela J. Wijeratne and Hong Ma
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00522.x
    Meiosis is essential for sexual reproduction and recombination is a critical step required for normalmeiosis. Understanding the underlying molecular mechanisms that regulate recombination is important for medical, agricultural and ecological reasons. Readily available molecular and cytological tools make Arabidopsis an excellent system to study meiosis. Here we review recent developments in molecular genetic analyses on meiotic recombination. These include studies on plant homologs of yeast and animal genes, as well as novel genes that were first identified in plants. The characterizations of these genes have demonstrated essential functions from the initiation of recombination by double-strand breaks to repair of such breaks, from the formation of double-Holliday junctions to possible resolution of these junctions, both of which are critical for crossover formation. The recent advances have ushered a new era in plant meiosis, in which the combination of genetics, genomics, and molecular cytology can uncover important gene functions.
Abstract (Browse 1588)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Mechanisms of Organelle Inheritance in Dividing Plant Cells  
Author: Michael B Sheahan, Ray J Rose and David W McCurdy
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00523.x
    Organelles form essential compartments of all eukaryotic cells. Mechanisms that ensure the unbiased inheritance of organelles during cell division are therefore necessary to maintain the viability of future cell generations. Although inheritance of organelles represents a fundamental component of the cell cycle, surprisingly little is known about the underlying mechanisms that facilitate unbiased organelle inheritance. Evidence from a select number of studies, however,indicates that ordered organelle inheritance strategies exist in dividing cells of higher plants. The basic requirement for unbiased organelle inheritance is the duplication of organelle volume and distribution of the resulting organelle populations in a manner that facilitates unbiased partitioning of the organelle population to each daughter cell. Often, partitioning strategies are specific to the organelle, being influenced by the functional requirements of the organelle and whether the cells are mitotically active or re-entering into the cell cycle. Organelle partitioning mechanisms frequently depend on interactions with either the actin or microtubule cytoskeleton. In this focused review, we attempt to summarize key findings regarding organelle partitioning strategies in dividing cells of higher plants. We particularly concentrate on the role of the cytoskeleton in mediating unbiased organelle partitioning.
Abstract (Browse 2042)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Inhibiting Self-Pollen: Self-Incompatibility in Papaver Involves Integration of Several Signaling Events  
Author: Vernonica E. Franklin-Tong
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00516.x
    Cellular responses rely on signal perception and integration. A nice example of this is self incompatibility (SI), which is an important mechanism to prevent inbreeding. It prevents self-fertilization by using a highly discriminatory cellular recognition and rejection mechanism. Most SI systems are genetically specified by the S-locus, which has a pollen and a pistil S-component. A receptor-ligand interaction is used by Papaver rhoeas to control SI. S proteins encoded by the pistil part of the S-locus interact with incompatible pollen to achieve rapid inhibition of tip growth. The incompatible SI interaction triggers a Ca2+-dependent signaling cascade. A number of SI-specific events are triggered in incompatible pollen, including rapid depolymerization of the actin cytoskeleton; phosphorylation of soluble inorganic pyrophosphatases (SPPases), Prp26.1;activation of a mitogen activated protein kinase, p56; programmed cell death (PCD) involving a caspase-3-like activity. These events contribute to prevent self-fertilization. We are attempting to establish the functional significance of these events, and their possible involvement in integrating a coordinated signaling response. Here we describe the identification of these components shown to be involved in SI, together with recent progress in identifying links between some of them. These data constitute the first steps in elucidating how SI signaling is integrated.
Abstract (Browse 1668)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Control of Directional Macromolecular Trafficking Across Specific Cellular Boundaries: A Key to Integrative Plant Biology  
Author: Biao Ding and Asuka Itaya
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00542.x
    There is now solid evidence that cell-to-cell trafficking of certain proteins and RNAs plays a critical role in trans-cellular regulation of gene expression to coordinate cellular differentiation and development. Such trafficking also is critical for viral infection and plant defense. The mechanisms of trafficking remain poorly understood. Although some proteins may move between cells by diffusion, many proteins and RNAs move in a highly regulated fashion. Regulation is likely achieved through interactions between distinct protein or RNA motifs and cellular factors. Some motifs and factors have been identified. One of the major focuses for future studies is to identify all motifs and their cognate factors and further elucidate their roles in trafficking between specific cells. With increasing information from such studies, we should be able to develop an understanding of the mechanisms that regulate trafficking of various proteins and RNAs across all and specific cellular boundaries. On the basis of such mechanistic knowledge, we can further investigate how the trafficking machinery has evolved to regulate developmental and physiological processes in a plant, how pathogens have co-evolved to use this machinery for systemic spread in a plant, and how plants use this machinery for counterdefense.
Abstract (Browse 1662)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
          Development & Photosynthesis
Alteration in Secondary Wall Deposition by Overexpression of the Fragile Fiber1 Kinesin-Like Protein in Arabidopsis  
Author: Jianli Zhou, Jia Qiu and Zheng-Hua Ye
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00521.x
    Secondary walls in fibers and vessels are typically deposited in three distinct layers, which are formed by the successive re-orientation of cellulose microfibrils. Although cortical microtubules have been implicated in this process, the underlying mechanisms for the formation of three distinct wall layers are not known. The Fragile Fiber1 (FRA1) kinesin-like protein has been previously shown to be involved in the oriented deposition of cellulose microfibrils and important for cell wall strength in Arabidopsis thaliana. In the present report, we investigated the expression pattern of the FRA1 gene and studied the effects of FRA1 overexpression on secondary wall deposition. The FRA1 gene was found to be expressed not only in cells undergoing secondary wall deposition including developing interfascicular fibers and xylem cells, but also in dividing cells and expanding/elongating parenchyma cells. Overexpression of FRA1 caused a severe reduction in the thickness of secondary walls in interfascicular fibers and deformation of vessels, which are accompanied with a marked decrease in stem strength. Close examination of secondary walls revealed that unlike the wild-type walls having three typical layers with the middle layer being the thickest, the secondary walls in FRA1 overexpressors exhibited an increased number of layers, all of which had a similar width. Together, these results provide further evidence implicating an important role of the FRA1 kinesin-like protein in the ordered deposition of secondary walls, which determines the strength of fibers and vessels.
Abstract (Browse 3511)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Transformations of the Pleiomorphic Plant MTOC during Sporogenesis in the Hepatic Marchantia polymorpha  
Author: Roy C. Brown, Betty E. Lemmon and Masaki Shimamura
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00539.x
    Sporogenesis in the hepatic Marchantia polymorpha L. provides an outstanding example of the pleiomorphic nature of the plant microtubule organizing center (MTOC). Microtubules are nucleated from ¶√-tubulin in MTOCs that change form during mitosis and meiosis. Following entry of cells into the reproductive pathway of sporogenesis, successive rounds of mitosis give rise to packets of 4®C16 sporocytes. Mitotic spindles are organized at discrete polar organizers (POs), a type of MTOC that is unique to this group of early divergent land plants. An abrupt and radical transformation in microtubule organization occurs when sporocytes enter meiosis: POs are lost and ¶√-tubulin is closely associated with surfaces of two large elongated plastids that subsequently divide into four. Migration of the four plastid MTOCs into a tetrahedral arrangement establishes the future spore domains and the division polarity of meiosis. As is typical of many bryophytes,cones of microtubules from the four plastid MTOCs initiate a quadripolar microtubule system (QMS) in meiotic prophase.At this point a transformation in the organization of the MTOCs occurs. The ¶√-tubulin detaches from plastids and forms a diffuse spheroidal pole in each of the spore domains. The plastids, which are no longer MTOCs, continue to divide. The diffuse MTOCs continue to nucleate cones ofmicrotubules during transformation of the QMS to a bipolar spindle. Following meiosis I, ¶√-tubulin is associated with nuclear envelopes, and the spindles of meiosis II are organized from diffuse MTOCs at the tetrad poles. At simultaneous cytokinesis, radial microtubule systems are organized at nuclear envelope MTOCs in each of the tetrad members.
Abstract (Browse 2044)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
          Signal Transduction
In Silico Identification of Co-transcribed Core Cell Cycle Regulators and Transcription Factors in Arabidopsis  
Author: Yixing Wang and Ming Yang
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00547.x
    Regulatory networks involving transcription factors and core cell cycle regulators are expected to play crucial roles in plant growth and development. In this report, we describe the identification of two groups of co-transcribed core cell cycle regulators and transcription factors via a two-step in silico screening. The core cell cycle regulators include TARDY ASYNCHRONOUS MEIOSIS (CYCA1;2), CYCB1;1, CYCB2;1, CDKB1;2, and CDKB2;2 while the transcription factors include CURLY LEAF, AINTEGUMENTA, a MYB protein, two Forkhead-associated domain proteins, and a SCARECROW family protein. Promoter analysis revealed a potential web of cross- and self-regulations among the identified proteins. Because one criterion for screening for these genes is that they are predominantly transcribed in young organs but not in mature organs, these genes are likely to be particularly involved in Arabidopsis organ growth.
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A Putative Calcium-Permeable Cyclic Nucleotide-Gated Channel, CNGC18, Regulates Polarized Pollen Tube Growth  
Author: Fang Chang, An Yan, Li-Na Zhao, Wei-Hua Wu and Zhenbiao Yang
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00524.x
    A tip-focused Ca2+ gradient is tightly coupled to polarized pollen tube growth, and tip-localized influxes of extracellular Ca2+ are required for this process. However the molecular identity and regulation of the potential Ca2+ channels remains elusive.The present study has implicated CNGC18 (cyclic nucleotide-gated channel 18) in polarized pollen tube growth, because its overexpression induced wider and shorter pollen tubes. Moreover, CNGC18 overexpression induced depolarization of pollen tube growth was suppressed by lower extracellular calcium ([Ca2+]ex). CNGC18-yellow fluorescence protein (YFP) was preferentially localized to the apparent post-Golgi vesicles and the plasma membrane (PM) in the apex of pollen tubes.The PM localization was affected by tip-localized ROP1 signaling. Expression of wild type ROP1 or an active form of ROP1 enhanced CNGC18-YFP localization to the apical region of the PM, whereas expression of RopGAP1 (a ROP1 deactivator) blocked the PM localization. These results support a role for PM-localized CNGC18 in the regulation of polarized pollen tube growth through its potential function in the modulation of calcium influxes.
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Primary Cell Wall Structure in the Evolution of Land Plants  
Author: Alex L. Nothnage and Eugene A. Nothnage
Journal of Integrative Plant Biology 2007 49(8)
DOI: 10.1111/j.1672-9072.2007.00519.x
    Investigation of the primary cell walls of lower plants improves our understanding of the cell biology of these organisms but also has the potential to improve our understanding of cell wall structure and function in angiosperms that evolved from lower plants. Cell walls were prepared from eight species, ranging from amoss to advanced gymnosperms, and subjected to sequential chemical extraction to separate the main polysaccharide fractions. The glycosyl compositions of these fractions were then determined by gas chromatography. The results were compared among the eight plants and among data from related studies reported in the existing published reports to identify structural features that have been either highly conserved or clearly modified during evolution. Among the highly conserved features are the presence of a cellulose framework, the presence of certain hemicelluloses such as xyloglucan, and the presence of rhamnogalacturonan II, a domain in pectic polysaccharides. Among the modified features are the abundance of mannosyl-containing hemicelluloses and the presence of methylated sugars.
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