ERA1 is essential for meristem growth in Arabidopsis thaliana.

The form of seed plants is determined by the growth of a number of meristems including apical meristems, leaf meristems and cambium layers. We investigated five recessive mutant alleles of a gene REVOLUTA that is required to promote the growth of apical meristems and to limit cell division in leaves and stems of Arabidopsis thaliana. REVOLUTA maps to the bottom of the fifth chromosome. Apical meristems of both paraclades (axillary shoots) and flowers of revoluta mutants frequently fail to complete normal development and form incomplete or abortive structures. The primary shoot apical meristem sometimes also arrests development early. Leaves, stems and floral organs, in contrast, grow abnormally large. We show that in the leaf epidermis this extra growth is due to extra cell divisions in the leaf basal meristem. The extent of leaf growth is negatively correlated with the development of a paraclade in the leaf axil. The thickened stems contain extra cell layers, arranged in rings, indicating that they may result from a cambium-like meristem. These results suggest that the REVOLUTA gene has a role in regulating the relative growth of apical and non-apical meristems in Arabidopsis.

Plant stem cells are a small group of cells with a self-renewal capacity and serve as a steady supply of precursor cells to form new differentiated tissues and organs in plants. Root stem cells and shoot stem cells, which are located in the root apical meristem and in the shoot apical meristem, respectively, play a critical role in plant longitudinal growth. These stem cells in shoot and root apical meristems remain as pluripotent state throughout the lifespan of the plant and control the growth and development of plants. The molecular mechanisms of initiation and maintenance of plant stem cells have been extensively investigated. In this review, we mainly discuss how the plant phytohormones, such as auxin and cytokinin, coordinate with the key transcription factors to regulate plant stem cell initiation and maintenance in root and shoot apical meristems. In addition, we highlight the common regulatory mechanisms of both root and shoot apical meristems.

As the development of research tools in molecular biology, plant developmental biology has been changed its focus from the descriptive analysis of plant morphology to the cellular and gene regulation level. Plants have distinct postembryonic development patterns compare to the animal, which give the plant a flexible developmental plasticity in response to different growth environments. In the long-term of evolution, plants are adapted to the environment changes through the continuous adjustment of their development strategy, which makes the plant world highly diverse. The growth and development of multicellular organisms depend on the maintenance and constant differentiation of stem cells. In plants, most of the organs originate from stem cells where resided in the shoot apical meristem, root apical meristem and cambium. The functional conservation of stem cells in those diverse plants is the basis for ontogenesis. However, from the perspective of evolutionary development, the diversity of key regulatory genes expression in different stem cell populations fulfills the continuous adjustments of development strategy to adapt to environmental changes. The plasticity in stem cell regulations determines the flexibility of plant development, which is conserved in plant kingdom from moss to angiosperms. Of course, the mechanism of stem cell maintenance and differentiation are even more complicated in angiosperms. In model plant of Arabidopsis thanian , the molecular mechanism of stem cell regulations has been extensively studied over the past decades. Multiple signaling molecules and transcription factors are found to tightly control the stem cell fate in Arabidopsis thaliana . The homeodomain transcription factor WUSCHEL ( WUS ) where expressed in the organizing center (OC) is a key regulator for plant stem cell fate determination. While, stem cells expressed secreted peptide CLV3, negatively regulates the expression of WUS . They form a negative feedback loop that tightly control plant stem cell fate. In addition, the classic phytohormones cytokinin and auxin also play essential roles in the maintenance of stem cells in shoot apical meristem, root apical meristem and cambium, and exhibit complex functional interactions. The molecular organization of the RAM is quite similar to that of the shoot. WOX5 ( WUSCHEL- RELATED HOMEOBOX 5 ), a homologue of WUS , is expressed in the QC, and induces root stem cell fate in the surrounding cells. The GRAS family transcription factor SHORT-ROOT ( SHR ) is expressed in the innermost tissue of the root, and SHR moves to the surrounding cell layer activating SCARECROW ( SCR ), together with PLT1 and PLT2 , defines the stem cells fate. In this review, we focused on the functions of plant stem cells in plant postembryonic development, and covered recent findings on plant hormonal regulation in stem cells. We also discussed the integration of endogenous genetic information and external environmental factors in plant development, and how they affected the development of organs, morphology and yield of crops.

In plants, changes in local auxin concentrations can trigger a range of developmental processes as distinct tissues respond differently to the same auxin stimulus. However, little is known about how auxin is interpreted by individual cell types. We performed a transcriptomic analysis of responses to auxin within four distinct tissues of the Arabidopsis thaliana root and demonstrate that different cell types show competence for discrete responses. The majority of auxin-responsive genes displayed a spatial bias in their induction or repression. The novel data set was used to examine how auxin influences tissue-specific transcriptional regulation of cell-identity markers. Additionally, the data were used in combination with spatial expression maps of the root to plot a transcriptomic auxin-response gradient across the apical and basal meristem. The readout revealed a strong correlation for thousands of genes between the relative response to auxin and expression along the longitudinal axis of the root. This data set and comparative analysis provide a transcriptome-level spatial breakdown of the response to auxin within an organ where this hormone mediates many aspects of development.

Spatial differences within the membrana granulosa in the expression of focimatrix and steroidogenic capacity

A comparative approach in biology is needed to assess the universality of rules governing this discipline. In plant telomere research, most of the key principles were established based on studies in only single model plant, Arabidopsis thaliana. These principles include the absence of telomere shortening during plant development and the corresponding activity of telomerase in dividing (meristem) plant cells. Here we examine these principles in Physcomitrella patens as a representative of lower plants. To follow telomerase expression, we first characterize the gene coding for the telomerase reverse transcriptase subunit PpTERT in P. patens, for which only incomplete prediction has been available so far. In protonema cultures of P. patens, growing by filament apical cell division, the proportion of apical (dividing) cells was quantified and telomere length, telomerase expression and activity were determined. Our results show telomere stability and demonstrate proportionality of telomerase activity and expression with the number of apical cells. In addition, we analyze telomere maintenance in mre11, rad50, nbs1, ku70 and lig4 mutants of P. patens and compare the impact of these mutations in double-strand-break (DSB) repair pathways with earlier observations in corresponding A. thaliana mutants. Telomere phenotypes are absent and DSB repair kinetics is not affected in P. patens mutants for DSB factors involved in non-homologous end joining (NHEJ). This is compliant with the overall dominance of homologous recombination over NHEJ pathways in the moss, contrary to the inverse situation in flowering plants.

The peptide ligands of the CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) family have been previously identified as essential signals for both short- and long-distance communication in plants, particularly during stem cell homeostasis, cell fate determination, and growth and development. To date, most studies on the CLE family have focused on model plants and especially those involving stem and apical meristems. Relatively little is known about the role of CLE peptides in tall trees and other plant meristems. In this review, we summarize the role of CLE genes in regulating plant Root Apical Meristem (RAM), Shoot Apical Meristem (SAM), Procambium, Leaf and Floral Meristem (FM), as well as their involvement in multiple signaling pathways. We also highlight the evolutionary conservation of the CLE gene family and provide a comprehensive summary of its distribution across various plant developmental tissues. This paper aims to provide insights into novel regulatory networks of CLE in plant meristems, offering guidance for understanding intercellular signaling pathways in forest trees and the development of new plant organs.

Higher plants maintain continuous development throughout their life by closely regulating the process of cell differentiation (Clark, 2001; Sablowski, 2007). In plants, the balance between undifferentiated and differentiated cell fate is managed within a stem cell niche termed the meristem. Cell differentiation in the meristem is in part controlled by genetic mechanisms. For example, mutations in CLAVATA (CLV) genes increase the number of undifferentiated cells within shoot and floral meristems leading to supernumerary organs (Clark, 2001). In contrast, mutations in genes of the homeodomain transcription factors WUSCHEL (WUS) and SHOOT-MERISTEMLESS (STM) lead to the absence of the shoot or floral meristem or its early termination through differentiation (Laux et al., 1996; Long et al., 1996). Cell differentiation in the meristem is also controlled by hormonal cues, which interfaces with gene function. For example, cytokinin treatment leads to phenotypes resembling clv mutants (Lindsay et al., 2006). Furthermore, exogenous cytokinin treatment has been shown to rescue the stm mutant phenotype and WUS protein has been shown to repress transcription of genes that act in the negative feedback pathway of cytokinin signaling (Leibfried et al., 2005; Yanai et al., 2005). The plant hormone auxin also plays a role in regulating differentiation. Auxin is thought to stimulate the initiation, development and differentiation of cells specified into organs (Teale et al., 2006). Disruption of auxin transport leads to a reduction in organ initiation and differentiation (Okada et al., 1991). In this thesis we investigate spatially regulated signaling and action of auxin and cytokinin which regulate patterning of gene expression and cell differentiation. To this end, we employed two model systems of shoot meristem initiation and development in the model plant Arabidopsis thaliana: shoot and floral meristem development and de novo shoot meristem initiation from tissue culture. Based on characterization of hormone signaling and patterning of gene expression during de novo shoot meristem initiation from tissue culture we propose a novel Turing-like model by which auxin and cytokinin interact to regulate patterning of cell differentiation. In this model, the activity of auxin, the activator of cell differentiation, is regulated by cytokinin, an inhibitor of cell differentiation. Computational models of these interactions lead to self organizing patterning of hormone response and cell differentiation as observed in experiments. In our second investigation, we show that cytokinin signaling regulates the spatial patterning of the homeodomain transcription factor WUS within the shoot meristem. We demonstrate that WUS misregulation after cytokinin treatment is mediated by both CLAVATA-dependent and independent mechanisms leading to multiple feedback loops. We reveal the presence of a cytokinin perception and signaling gradient within the shoot meristem, which spatially influences size and position of the WUS domain. Finally, we have begun to identify the molecular components required for cytokinin activation of WUS expression. Of the three characterized cytokinin receptors, only Arabidopsis Histidine Kinase 2 (AHK2) is required for WUS induction in the presence of cytokinin. In contrast, the AHK3 receptor is required for negative feedback on cytokinin signaling and thus WUS. These data reveal an unappreciated specificity in cytokinin signaling in regulating downstream targets which may be important for eliciting different cell behaviors depending on the threshold of signaling and the ratio of the three cytokinin receptors within a given cell.

Genes that integrate multiple adipogenic signaling pathways in human mesenchymal stem cells

Postembryonic development in plants depends on the activity of the shoot apical meristem (SAM) and root apical meristem (RAM). In Arabidopsis thaliana, CLAVATA signaling negatively regulates the size of the stem cell population in the SAM by repressing WUSCHEL. In other plants, however, studies of factors involved in stem cell maintenance are insufficient. Here, we report that two proteins closely related to CLAVATA3, FLORAL ORGAN NUMBER2 (FON2) and FON2-LIKE CLE PROTEIN1 (FCP1/Os CLE402), have functionally diversified to regulate the different types of meristem in rice (Oryza sativa). Unlike FON2, which regulates the maintenance of flower and inflorescence meristems, FCP1 appears to regulate the maintenance of the vegetative SAM and RAM. Constitutive expression of FCP1 results in consumption of the SAM in the vegetative phase, and application of an FCP1 CLE peptide in vitro disturbs root development by misspecification of cell fates in the RAM. FON1, a putative receptor of FON2, is likely to be unnecessary for these FCP1 functions. Furthermore, we identify a key amino acid residue that discriminates between the actions of FCP1 and FON2. Our results suggest that, although the basic framework of meristem maintenance is conserved in the angiosperms, the functions of the individual factors have diversified during evolution.

Local efflux-dependent auxin gradients and maxima mediate organ and tissue development in plants. Auxin efflux is regulated by dynamic expression and subcellular localization of the PIN auxin-efflux proteins, which appears to be established not only through a self-organizing auxin-mediated polarization mechanism, but also through other means, such as cell fate determination and auxin-independent mechanisms. Here, we show that the Arabidopsis thaliana NO VEIN (NOV) gene, encoding a novel, plant-specific nuclear factor, is required for leaf vascular development, cellular patterning and stem cell maintenance in the root meristem, as well as for cotyledon outgrowth and separation. nov mutations affect many aspects of auxin-dependent development without directly affecting auxin perception. NOV is required for provascular PIN1 expression and region-specific expression of PIN7 in leaf primordia, cell type-specific expression of PIN3, PIN4, and PIN7 in the root, and PIN2 polarity in the root cortex. NOV is specifically expressed in developing embryos, leaf primordia, and shoot and root apical meristems. Our data suggest that NOV function underlies cell fate decisions associated with auxin gradients and maxima, thus establishing cell type-specific PIN expression and polarity. We propose that NOV mediates the acquisition of competence to undergo auxin-dependent coordinated cell specification and patterning, thereby eliciting context-dependent auxin-mediated developmental responses.

BackgroundTransverse cortical microtubule orientation, critical for anisotropic cell expansion, is established in the meristematic root zone. Intending to elucidate the possible prerequisites for this establishment and factors that are involved, microtubule organization was studied in roots of Arabidopsis thaliana, wild-type and the p60-katanin mutants fra2, ktn1-2 and lue1. Transverse cortical microtubule orientation in the meristematic root zone has proven to persist under several regimes inhibiting root elongation. This persistence was attributed to the constant moderate elongation of meristematic cells, prior to mitotic division. Therefore, A. thaliana wild-type seedlings were treated with aphidicolin, in order to prevent mitosis and inhibit premitotic cell elongation.ResultsIn roots treated with aphidicolin for 12 h, cell divisions still occurred and microtubules were transverse. After 24 and 48 h of treatment, meristematic cell divisions and the prerequisite elongation ceased, while microtubule orientation became random. In meristematic cells of the p60-katanin mutants, apart from a general transverse microtubule pattern, cortical microtubules with random orientation were observed, also converging at several cortical sites, in contrast to the uniform transverse pattern of wild-type cells.ConclusionTaken together, these observations reveal that transverse cortical microtubule orientation in the meristematic zone of A. thaliana root is cell division-dependent and requires severing by katanin.

Cell biological, structural, and genetic approaches have demonstrated the presence of arabinogalactan proteins (AGPs) in the moss Physcomitrella patens and provided evidence for their function in cell expansion and specifically in the extension of apical tip-growing cells. Inhibitor studies indicated that apical cell expansion in P. patens is blocked by synthetic AGP binding beta-glucosyl Yariv reagent (betaGlcYR). The anti-(1-->5)-alpha-L-arabinan monoclonal antibody LM6 binds to some AGPs in P. patens, to all plasma membranes, and to the cell wall surface at the most apical region of growing protonemal filaments. Moreover, LM6 labeling of cell walls at the tips of apical cells of P. patens was abolished in the presence of betaGlcYR, suggesting that the localized movement of AGPs from the plasma membrane to the cell wall is a component of the mechanism of tip growth. Biochemical and bioinformatic analyses were used to identify seven P. patens ESTs encoding putative AGP core proteins from homology with Arabidopsis thaliana, Brassica napus, and Oryza sativa sequences and from peptide fragments isolated from betaGlcYR-precipitated AGPs. Gene knockout by homologous recombination of one of these genes, P. patens AGP1, encoding a classical AGP core protein, resulted in reduced cell lengths in protonemal filaments, indicating a role for AGP1 in apical cell expansion in P. patens.

植物的环境信号分子茉莉酸及其生物学功能

Author response: A single-cell transcriptome atlas of pig skin characterizes anatomical positional heterogeneity