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PubMed2001

Expression of the mitogen-activated protein kinase kinase ZmMEK1 in the primary root of maize.

We have analyzed changes in the distribution and abundance of a mitogen-activated protein kinase kinase (MAPKK) enzyme (EC 2.7.1.37) known as ZmMEK1. in root apices of Zea mays L. under normal growth conditions, and after treatments that alter patterns of proliferation, as a means to assess the potential physiological role of the MAP kinase cascade in growth and development. The ZmMEK1 protein is most abundant within immature tissues such as the roots and leaves of seedlings, and is nearly undetectable in mature leaf tissue. Along the longitudinal axis of growing roots, ZmMEK1 mRNA and protein are abundant throughout the apical 12 mm. Two anti-ZmMEK1 antibody-reactive proteins can be resolved within the apical 4 mm of the root, spatially coinciding with the meristem and distal elongation zone. Phosphatase treatments suggest that both immunoreactive bands are forms of ZmMEK1 that differ in their state of phosphorylation. Expression of ZmMEK1, histone H4 and cyclin-dependent protein kinase (CDK) in roots after 7 days of exposure to low temperature and during a 48-hour recovery period was monitored during the coincident alterations in growth. Levels of ZmMEK1 mRNA and protein within these roots were indistinguishable from those of control roots. However, a slower-migrating form of ZmMEK1 temporally coincided with the observed increase in CDK levels during the transition into proliferative activity. We demonstrate that the ZmMEK1 MAPK activator is expressed and is differentially phosphorylated within the root meristem and distal elongation zone. We suggest that post-translational modifications of the protein regulate the function of ZmMEK1 within the root. Changes in ZmMEK1 phosphorylation state correlate with changes in proliferation in the root apex.

DNA-Binding Proteins↗

PubMed2002

The Arabidopsis gene PEPINO/PASTICCINO2 is required for proliferation control of meristematic and non-meristematic cells and encodes a putative anti-phosphatase.

Growth in organisms requires that cell division versus differentiation are precisely controlled and that cells, once differentiated, do not resume proliferation activity. Mutants of the Arabidopsis gene PEPINO/PASTICCINO2 develop abnormal shoot phenotypes from slow tumour-like cell proliferation. Abnormal proliferation is enhanced in a mutant background, which elevates endogenous cytokinin levels as seen in double mutants of pepino and altered meristem primordia1. The enlarged shoot apical meristem produces supernumerary abnormal leaves. However, comparison of expression patterns of Cyclin1At and the homeobox gene KNAT2 indicates that PEPINO ( PEP) is involved in cell cycle regulation of meristematic and non-meristematic cells. PEP encodes a putative anti-phosphatase, a representative of an enigmatic class of proteins, which might participate in proliferation processes. In mammals at least two proteins, Sbf1 and STYX, have been predicted to represent functional anti-phosphatases controlling cell proliferation. However, the in vivo function of this class of molecules is not known since no loss-of-function mutants have been reported to date. Anti-phosphatases display a natural change of the essential cysteine by glycine in the phosphatase catalytic signature motif HCxxGxxR(S/T). The remaining motif harbours highly conserved amino acid residues and is thought to constitute a pocket that enables such proteins to bind but not catalyse phosphorylated residues. One of the sequenced mutations in PEP indicates that the integrity of this anti-phosphatase signature motif is essential for function. The analysis of pepino, the first known loss-of-function mutant of an anti-phosphatase in a multicellular organism, proves the biological significance of these molecules.

Amino Acid Sequence↗

PubMed1999

Molecular cloning and characterisation of a maize cDNA for a homologue of the large subunit of the eukaryotic initiation factor 3 (eIF3).

In order to identify genes that are specifically expressed in distinct cell populations of the maize root apex, we have constructed PCR-directed cDNA libraries from microdissected populations of cells, and screened them by differential hybridisation. A meristem-specific cDNA was isolated and characterised. This cDNA, termed ZmeIF3A, encodes a protein homologous to the large subunit of the eukaryotic translation Initiation Factor 3 (eIF3), which is an essential multi-protein complex for the initiation of protein synthesis. The ZmeIF3A protein is most similar to the yeast homologue RPG1, lacking the repeated C-terminal domain characteristic of its mammalian counterparts. However, despite this similarity, it fails to replace the RPG1 protein in complementation experiments on yeast mutants. Analysis of gene expression in situ showed that the ZmeIF3A transcript is expressed in the region of the root meristem surrounding the central stele. ZmeIF3A mRNA is also expressed in the young root, the male inflorescence, and the developing cob and seed. In maize, ZmeIF3A is encoded by one or two genomic sequences. This is the first report on the isolation and characterisation of a cDNA from higher plants that encodes a product homologous to a component of the eIF3 complex.

Amino Acid Sequence↗

PubMed1999

Homologs of animal eyes absent (eya) genes are found in higher plants.

Homologs of the eyes absent (eya) gene in animals function at multiple stages in the development of organs. Their functional roles in the genetic network that regulates eye development in Drosophila have recently been extensively analyzed. A rice homolog of eya was identified from a cDNA library made from embryo RNA. The corresponding gene (OSEya1) encodes a conserved ED1 domain and a short N-terminal peptide. The ED1 domain of OSEya1 shows 25% identity and 36% similarity to the product of Drosophila eya. Mammalian and squid eya homologs show about 35% similarity to OSEya1. Homologous sequences were also found in the alfalfa EST database (53% identity and 65% similarity to OSEya1) and in the Arabidopsis genome sequence (63% identity). Therefore, eya homologs are present in both monocots and dicots. Three regions in the ED1 domain are well conserved in animals and plants. Plant eya products deduced from the nucleotide sequences also have short N-terminal peptides. The OSEya1 gene is located between the wx gene and the telomere on the short arm of chromosome 6. OSEya1 is expressed in the embryo, shoot apex, and caryopsis in rice. Expression in the embryo increases during embryogenesis until 7 days after pollination, with preferential localization in leaf primordia and the shoot apical meristem. Expression in the influorescence was observed in floral meristems. The functions of OSEya1 in higher plants are discussed and compared with those of their animal homologs. OSEya1 might regulate the morphogenesis of lateral organs as a subunit of a transcription factor.

Amino Acid Sequence↗

PubMed2004

Arabidopsis whole-transcriptome profiling defines the features of coordinated regulations that occur during secondary growth.

Secondary growth in the inflorescence stems of Arabidopsis plants was induced by a combination of short-day and long-day treatments. The induced stems were divided into three different stem developmental stages (i.e., immature, intermediate, and mature) with regard to secondary growth. Whole transcriptome microarrays were used to examine the changes in global gene expression occurring at the different stem developmental stages. Over 70% of the Arabidopsis transcriptome was expressed in the stem tissues. In the mature stems with secondary growth, 567 genes were upregulated 5-fold or higher and 530 were downregulated, when compared to immature stems (with no secondary growth) and 10-day old seedlings (with no inflorescence stem). The transcription phenotypes obtained from the stems at different developmental stages largely confirm the existing insights into the biochemical processes involved in the sequential events that lead to wood formation. The major difference found between the stems undergoing secondary growth and only primary growth was in the expression profiles of transcriptional regulation-and signal transduction-related genes. An analysis of several shoot apical meristem (SAM) activity-related gene expression patterns in the stems indicated that the genetic control of secondary meristem activity might be governed by a different mechanism from that of SAM. The current study established the expression patterns of many unknown genes and identified candidate genes that are involved in the genetic regulation of secondary growth. The findings described in this report should improve our understanding of the molecular mechanisms that regulate the growth and development of the stem.

Apoptosis↗

PubMed2006

Quantitative analyses of cell division in plants.

At the molecular level regulatory interactions between cell cycle genes are being uncovered rapidly, but less progress is made in unravelling how these molecular events regulate growth processes at the level of cells and of the whole organism. The main obstacle is the absence of a set of analytical tools that are powerful enough to determine pertinent parameters and, at the same time, relatively easy to use by non-specialized laboratories. Appropriate methodology to obtain this type of data has been pioneered in the first half of the last century and is now commonly defined as 'kinematic analysis'. Unfortunately, the laborious nature of these analyses and the relatively complex numerical methods used, have limited their use to only a handful of specialized research groups. In this article we attempt to present an accessible entry to this methodology, particularly in terms of the mathematical framework. We start describing the simplest possible system, i.e., a virtually homogenous cell suspension culture. Then, we outline the analysis of dicotyledonous leaves, root tips, monocotyledonous leaves, and finally shoot apical meristems. For each of these systems we discuss the details of the calculation of cell division parameters such as cell cycle duration, size of the meristem and number of cells contained in it, which enables answering fundamental questions about the relative contribution of differences in cell production and cell size to variation in growth. In addition, we discuss the assumptions and limitations of these and alternative methodologies with the aim to facilitate the choice of appropriate analyses depending on the specific research question.

Arabidopsis↗

PubMed2006

KNOX gene function in plant stem cell niches.

Homeobox genes encode transcriptional regulators that control development in multicellular eukaryotes. In plants, post-embryonic shoot growth relies on the activity of indeterminate cell populations termed shoot meristems, within which members of the class-1 KNOX sub-family of homeobox genes are expressed. KNOX genes are differentially required for meristem development and function to inhibit cell expansion and differentiation associated with organogenesis. Mechanisms must therefore be employed to prevent KNOX gene expression in developing lateral organs such as leaves. This review focuses on the expression patterns, meristematic functions and regulation of KNOX genes, and how the activities of these genes are integrated within the framework of pathways that control plant development.

Arabidopsis↗

PubMed2006

Stem cell signalling networks in plants.

The essential nature of meristematic tissues is addressed with reference to conceptual frameworks that have been developed to explain the behaviour of animal stem cells. Comparisons are made between different types of plant meristems with the objective of highlighting common themes that might illuminate underlying mechanisms. A more in depth comparison of the root and shoot apical meristems is made which suggests a common mechanism for maintaining stem cells. The relevance of organogenesis to stem cell maintenance is discussed, along with the nature of underlying mechanisms which help ensure that stem cell production is balanced with the depletion of cells through differentiation. Mechanisms that integrate stem cell behaviour in the whole plant are considered, with a focus on the roles of auxin and cytokinin. The review concludes with a brief discussion of epigenetic mechanisms that act to stabilise and maintain stem cell populations.

Cell Differentiation↗

PubMed2006

Characterization of T-DNA insertion mutants and RNAi silenced plants of Arabidopsis thaliana UV-damaged DNA binding protein 2 (AtUV-DDB2).

The human UV-damaged DNA binding protein (UV-DDB), a heterodimeric protein composed of 127 kDa (UV-DDB1) and 48 kDa (UV-DDB2) subunits, has been shown to be involved in DNA repair. To elucidate the in vivo function of plant UV-DDB2, we have analyzed T-DNA insertion mutants of the Arabidopsis thaliana UV-DDB2 subunit (atuv-ddb2 mutants) and AtUV-DDB2 RNAi silenced plants (atuv-ddb2 silenced plants). atuv-ddb2 mutants and atuv-ddb2 silenced plants were both viable, suggesting that AtUV-DDB2 is not essential for survival. Interestingly, both plant types showed a dwarf phenotype, implying impaired growth of the meristem. To the best of our knowledge, this is the first occasion that a dwarf phenotype has been found to be associated with a UV-DDB2 mutation in either plants or animals. The mutants also demonstrated increased sensitivity to UV irradiation, methyl methanesulfonate and hydrogen peroxide treatment, indicating that AtUV-DDB2 is also involved in DNA repair. Our results lead us to suggest that not only does AtUV-DDB2 function in DNA repair, it also has a direct or indirect influence on cell proliferation in the plant meristem.

Arabidopsis↗

PubMed2006

The FT/TFL1 gene family in grapevine.

The FT/TFL1 gene family encodes proteins with similarity to phosphatidylethanolamine binding proteins which function as flowering promoters and repressors. We show here that the FT/TFL1 gene family in Vitis vinifera is composed of at least five genes. Sequence comparisons with homologous genes identified in other dicot species group them in three major clades, the FT, MFT and TFL1 subfamilies, the latter including three of the Vitis sequences. Gene expression patterns are in agreement with a role of VvFT and VvMFT as flowering promoters; while VvTFL1A, VvTFL1B and VvTFL1C could be associated with vegetative development and maintenance of meristem indetermination. Overexpression of VvFT in transgenic Arabidopsis plants generates early flowering phenotypes similar to those produced by FT supporting a role for this gene in flowering promotion. Overexpression of VvTFL1A does not affect flowering time but the determination of flower meristems, strongly altering inflorescence structure, which is consistent with the biological roles assigned to similar genes in other species.

Amino Acid Sequence↗

PubMed1995

The improved Allium/Vicia root tip micronucleus assay for clastogenicity of environmental pollutants.

The meristematic mitotic cells of plant roots are appropriate and efficient cytogenetic materials for the detection of clastogenicity of environmental pollutants, especially for in situ monitoring of water contaminants. Among several cytological endpoints in these fast dividing cells, such as chromosome/chromatid aberrations, sister-chromatid exchanges and micronuclei, the most effective and simplest indicator of cytological damage is micronucleus formation. Although the Allium cepa and Vicia faba root meristem micronucleus assays (Allium/Vicia root MCN) have been used in clastogenicity studies about 12 times by various authors in the last 25 years, there is no report on the comparison of the efficiency of these two plant systems and in different cell populations (meristem and F1) of the root tip as well as under adequate recovery duration. In order to maximize the efficiency of these bioassays, the current study was designed to compare the Allium and the Vicia root MCN assays on the basis of chromosome length, peak sensitivity of the mitotic cells, and the regions of the root tip where the MCN are formed. The total length of the 2n complement of Allium chromosomes is 14.4 microns and the total length of the 2n complement of Vicia is 9.32 microns. The peak sensitivity determined by serial fixation at 12-h intervals after 100 R of X-irradiation is 44 h. The slope of the X-ray dose-response curve of Allium roots derived from the meristematic regions was lower than that derived from cells in the F1 region. Higher efficiency was also demonstrated when the MCN frequencies were scored from the F1 cells in both Allium and Vicia treated with formaldehyde (FA), mitomycin C (MMC), and maleic hydrazide (MH). The results indicated that scoring of MCN frequencies from the F1 cell region of the root tip was more efficient than scoring from the meristematic region. The X-ray linear regression dose-response curves were established in both Allium and Vicia cell systems and the coefficients of correlations, slope values were used to verify the reliability and efficiency of these two plant cell systems. Based on the dose-response slope value of 0.894 for Allium and 0.643 for Vicia, the Allium root MCN was a more efficient test system. The greater sensitivity of the Allium roots is probably due to the greater total length of the diploid complement and the higher number of metacentric chromosomes.(ABSTRACT TRUNCATED AT 400 WORDS)

Allium↗

PubMed1986

[Cellular differentiation and proliferation in corn roots grown in microgravity (Biocosmos 1985)].

A cytological study was performed on Maize roots (Zea mays) which were grown in space (flight Biocosmos 1985) and on control roots on earth. Two criteria were selected: cell elongation in the cortical zone in the four mm of the extremity of the root and mitotic activity of the meristem. The results show that in microgravity the length of the meristem is reduced of 1/3 and that its mitotic activity increases of about twofold comparatively to the synchronous control. In parallel the cell differentiation begin closer to the root cap junction. These results are discussed relative to the influence of gravistimulation on cell proliferation and cell differentiation in roots.

Cell Differentiation↗

PubMed1994

Pattern formation in plant development: four vignettes.

In their development, plants precisely control the patterns of cell size, cell shape and cell division, the position of differentiation of cell types, and the position and number of organs. In the past year, progress has been made in understanding four of these five levels of control of plant pattern formation, including specification of cell fate by cell size in the alga Volvox carteri, genetic control of cell shape in the leaf hairs of the flowering plant Arabidopsis thaliana, precise control of cell division and cellular enlargement in Arabidopsis root meristems, and control of cell number in meristems of Arabidopsis, tobacco, and maize. These examples indicate that both the fate and shape of differentiated plant cells can be determined by the size of their undifferentiated precursors, and that the primary effect of mutations that alter cell fate and cellular shape can be on cell size. Furthermore, specific genes have been found that are necessary for normal patterns and numbers of cell divisions. Molecular cloning of these genes is revealing the molecular basis of plant cell division control.

Arabidopsis↗

PubMed2004

Biological effects due to weak magnetic field on plants.

Throughout the evolution process, Earth's magnetic field (MF, about 50 microT) was a natural component of the environment for living organisms. Biological objects, flying on planned long-term interplanetary missions, would experience much weaker magnetic fields, since galactic MF is known to be 0.1-1 nT. However, the role of weak magnetic fields and their influence on functioning of biological organisms are still insufficiently understood, and is actively studied. Numerous experiments with seedlings of different plant species placed in weak magnetic field have shown that the growth of their primary roots is inhibited during early germination stages in comparison with control. The proliferative activity and cell reproduction in meristem of plant roots are reduced in weak magnetic field. Cell reproductive cycle slows down due to the expansion of G1 phase in many plant species (and of G2 phase in flax and lentil roots), while other phases of cell cycle remain relatively stable. In plant cells exposed to weak magnetic field, the functional activity of genome at early pre-replicate period is shown to decrease. Weak magnetic field causes intensification of protein synthesis and disintegration in plant roots. At ultrastructural level, changes in distribution of condensed chromatin and nucleolus compactization in nuclei, noticeable accumulation of lipid bodies, development of a lytic compartment (vacuoles, cytosegresomes and paramural bodies), and reduction of phytoferritin in plastids in meristem cells were observed in pea roots exposed to weak magnetic field. Mitochondria were found to be very sensitive to weak magnetic field: their size and relative volume in cells increase, matrix becomes electron-transparent, and cristae reduce. Cytochemical studies indicate that cells of plant roots exposed to weak magnetic field show Ca2+ over-saturation in all organelles and in cytoplasm unlike the control ones. The data presented suggest that prolonged exposures of plants to weak magnetic field may cause different biological effects at the cellular, tissue and organ levels. They may be functionally related to systems that regulate plant metabolism including the intracellular Ca2+ homeostasis. However, our understanding of very complex fundamental mechanisms and sites of interactions between weak magnetic fields and biological systems is still incomplete and still deserve strong research efforts.

Calcium↗

PubMed2006

[Physiological and structural modifications induced by cadmium-calcium interaction in tomato (Lycopersicon esculentum)].

Tomato seedlings (Lycopersicon esculentum), initially cultivated in a basic nutrient solution during 12 days, were treated with increasing CdCl(2) concentrations for 10 days. The results showed that cadmium inhibited the weight growth depending on the metal concentration and the plant organ. In the presence of 20 microM CdCl(2), the addition of calcium, 0.1 to 10 mM of CaCl(2) in the culture medium, improved especially the biomass production and the mineral composition of the plants in concomitance with an increase in the contents of photosynthetic pigments. Histological study at the hypocotyle level revealed that cadmium (20 microM) induced a restriction of the tissue territories as well as meristem formations differentiating in a root structure. At this concentration, the addition of CaCl(2) (5 microM) was characterized by an opposite effect with absence of meristem structures. The overall results suggest that the alteration of some plant growth process after exposure to cadmium can be attenuated by an adequate calcium contribution in culture medium.

Cadmium↗

PubMed2004

Competence to respond to floral inductive signals requires the homeobox genes PENNYWISE and POUND-FOOLISH.

The transition from vegetative to reproductive development establishes new growth patterns required for flowering. This switch is controlled by environmental and/or intrinsic developmental cues that converge at the shoot apical meristem (SAM). During this developmental transition, floral inductive signals cause the vegetative meristem to undergo morphological changes that are essential for flowering. Arabidopsis plants containing null mutations in two paralogous BEL1-like (BELL) homeobox genes, PENNYWISE (PNY) and POUND-FOOLISH (PNF), disrupt the transition from vegetative to reproductive development. These double mutants are completely unable to flower even though the SAM displays morphological and molecular changes that are consistent with having received floral inductive signals. These studies establish a link between the competence to receive floral inductive signals and restructuring of the SAM during floral evocation.

Arabidopsis↗

PubMed2003

Growing up green: cellular basis of plant development.

Plant development is a biphasic process. Pattern formation during embryogenesis generates a basic body organisation, including self-maintaining stem-cell systems called meristems at opposite ends of the main axis of polarity. During post-embryonic development, the meristems produce new organs with reference to the existing body, transforming the juvenile seedling into the species-specific adult plant. Studies in Arabidopsis indicate that patterning in plants involves not only cell surface interactions but also unique modes of communication such as movement of transcription factors between cells and directional transport of the signaling molecule auxin.

Arabidopsis↗

PubMed2004

Shaping up: the genetic control of leaf shape.

Leaf initiation at the shoot apical meristem involves a balance between cell proliferation and commitment to make primordia. Several genes, such as CLAVATA1, CLAVATA3, WUSCHEL, KNOTTED1, and PHANTASTICA, play key roles in these processes. When expressed in the leaf primordium, however, these 'meristem' genes can profoundly affect leaf shape and size, possibly by regulating hormone gradients and transport. The KNOTTED1-like genes are involved in regulating changes in hormonal levels. Recent studies have elaborated on the role that hormones, such as auxin, play in releasing biophysical constraints on leaf initiation and growth. Final leaf form is elaborated by a coordination of these hormonally regulated processes, cell division and cellular differentiation.

Cell Division↗