SEARCH · PubMed Health

Results for “Meristem”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources

PubMed1997

Short-range control of cell differentiation in the Arabidopsis root meristem.

Meristems are distinctive regions of plants that have capacity for continuous growth. Their developmental activity generates the majority of plant organs. It is currently unknown how cell division and cell differentiation are orchestrated in meristems, although genetic studies have demonstrated the relevance of a proper balance between the two processes. Root meristems contain a distinct central region of mitotically inactive cells, the quiescent centre, the function of which has remained elusive until now. Here we present laser ablation and genetic data that show that in Arabidopsis thaliana the quiescent centre inhibits differentiation of surrounding cells. Differentiation regulation occurs within the range of a single cell, in a manner strikingly similar to examples in animal development, such as during delamination of Drosophila neuroblasts. Our data indicate that pattern formation in the root meristem is controlled by a balance between short-range signals inhibiting differentiation and signals that reinforce cell fate decisions.

Arabidopsis↗

PubMed2000

Axillary meristem development in Arabidopsis thaliana.

Axillary shoot apical meristems initiate post-embryonically in the axils of leaves. Their developmental fate is a main determinant of the final plant body plan. In Arabidopsis, usually a single axillary meristem initiates in the leaf axil even though there is developmental potential for formation of multiple branches. While the wild-type plants rarely form multiple branches in the leaf axil, tfl1-2 plants regularly develop two or more branches in the axils of the rosette leaves. Axillary meristem formation in Arabidopsis occurs in two waves: an acropetal wave forms during plant vegetative development, and a basipetal wave forms during plant reproductive development. We report here the morphological and anatomical changes, and the STM expression pattern associated with the formation of axillary and accessory meristems during Arabidopsis vegetative development.

Arabidopsis↗

PubMed2001

Novel marker genes for early leaf development indicate spatial regulation of carbohydrate metabolism within the apical meristem.

To identify genes expressed at the earliest stages of leaf development, we have performed a differential display analysis using portions of meristems destined to form leaves. Our analysis led to the identification of five genes showing an asymmetric pattern of gene expression within the meristem associated with leaf formation. Surprisingly, three of these genes encoded enzymes involved in carbohydrate metabolism (ADPglucose pyrophosphorylase, sucrose synthase and an SNF1-like kinase). Furthermore, specific transcript patterns were responsive to specific sugar and hormonal treatments. The other two genes identified encoded a Phantastica-like myb transcription factor (associated with the acquisition of leaf dorsiventrality) and CYP85 (a cytochrome P450, which plays a pivotal role in brassinolide metabolism). These data, firstly, identify a novel set of marker genes for the analysis of the earliest stages of leaf formation. Secondly, the function of the proteins encoded by these genes and their expression patterns within the meristem indicate that carbohydrate metabolism is spatially regulated within a tissue involved in key developmental processes. Finally, our data provide the first indication of an asymmetry in gene expression related to hormone biosynthesis in the meristem.

Amino Acid Sequence↗

PubMed2001

The MADS-box gene DEFH28 from Antirrhinum is involved in the regulation of floral meristem identity and fruit development.

DEFH28 is a novel MADS-box gene from Antirrhinum majus. Phylogenetic reconstruction indicates that it belongs to the SQUA-subfamily of MADS-box genes. Based on its expression pattern and the phenotype of transgenic plants it is predicted that DEFH28 exerts a dual function during flower development, namely control of meristem identity and fruit development. Firstly, DEFH28 is expressed in the inflorescence apical meristem and might control, together with SQUAMOSA (SQUA), floral meristem identity in Antirrhinum. Also, DEFH28 is sufficient to switch inflorescence shoot meristem to a floral fate in transgenic Arabidopsis thaliana plants. Secondly, DEFH28 is expressed in carpel walls, where it may regulate carpel wall differentiation and fruit maturation. Support for this later role comes from overexpression of DEFH28 throughout the silique in transgenic Arabidopsis plants where it altered the identity of the replum and valve margin cells so that they adopted a valve cell identity. This late aspect of the DEFH28 function is identical to the FRUITFULL (FUL) function of Arabidopsis as demonstrated in gain-of-function plants. FUL, like DEFH28, belongs to the SQUA-subfamily of MADS-box genes. DEFH28 most likely represents the ortholog of FUL. Promoter analysis shows that the control mechanism conferring a carpel wall specific expression has been conserved between Antirrhinum and Arabidopsis during evolution. Although the overall flower development between Antirrhinum and Arabidopsis is very similar, their carpels mature into different types of fruits: capsules and siliques, respectively. Therefore, it is suggested that the role of DEFH28 in control of carpel wall differentiation reflects a conserved molecular mechanism integrated into two very different carpel developmental pathways.

Amino Acid Sequence↗

PubMed2003

Cell division pattern influences gene expression in the shoot apical meristem.

The shoot apical meristem of angiosperms shows a highly conserved cellular architecture in which a change of cell division orientation correlates with early events of leaf initiation. However, the causal role of this altered cellular parameter in leaf formation is debatable. We have used the dynamin-like protein phragmoplastin as a tool to modify the pattern of cell division within the apical meristem. Taking a microinduction approach, we show that local alteration in cell division orientation is not sufficient to induce morphogenesis in the meristem. Surprisingly, an altered cell division pattern did lead to an altered pattern of expression of genes implicated in aspects of leaf formation. Our data identify inducible expression of phragmoplastin as a tool to manipulate cell division pattern. Furthermore, they indicate that a mechanism exists by which cells in the meristem can respond at the level of gene expression to altered parameters of cell division. These data are discussed in the context of a model linking leaf morphogenesis and differentiation.

Cell Division↗

PubMed2003

Arabidopsis histone acetyltransferase AtGCN5 regulates the floral meristem activity through the WUSCHEL/AGAMOUS pathway.

Histone acetyltransferases, which are able to acetylate histone and non-histone proteins, play important roles in gene regulation. Many histone acetyltransferases are related to yeast Gcn5, a component of two transcription regulatory complexes SAGA and ADA. In this work, by characterizing a mutation in the Arabidopsis GCN5 gene (AtGCN5) we studied the regulatory function of this gene in controlling floral meristem activity. We show that in addition to pleiotropic effects on plant development, this mutation also leads to the production of terminal flowers. The flowers show homeotic transformations of petals into stamens and sepals into filamentous structures and produce ectopic carpels. The phenotypes correlate to an expansion of the expression domains within floral meristems of the key regulatory genes WUSCHEL (WUS) and AGAMOUS (AG). These results suggest that AtGCN5 is required to regulate the floral meristem activity through the WUS/AG pathway. This study brings new elements on the elucidation of specific developmental pathways regulated by AtGCN5 and on the control mechanism of meristem regulatory gene expression.

Acetyltransferases↗

PubMed1992

Changes in ratio of soluble sugars and free amino nitrogen in the apical meristem during floral transition of tobacco.

Under a modification of the nutrient diversion hypothesis, we propose that an inequality in carbohydrate and nitrogen translocation to the apical meristem may be a controlling factor in floral transition. Experiments were conducted in controlled-environment chambers to determine the associations between microscopic characteristics of the transition from vegetative to floral stages of the apical meristem of flue-cured tobacco and to assimilate concentrations in the plant and apical meristem. Low temperature, nitrogen withdrawal, and restriction of nitrogen uptake were used as treatment variables. In all of these stress treatments, flowering occurred at a lesser number of leaves than in control treatments. Low temperature stress accelerated the time of transition to the floral stage as compared with a high temperature control; however, nitrogen stress did not accelerate the time of transition. All stress treatments affected the levels of nitrogen and carbohydrate in whole plants. Most notable was an increase in the percentage of starch and a decrease in the percentage of total soluble carbohydrate induced by the stress treatments. These data indicate that tobacco plants under stress accumulate excess carbohydrate in the form of starch. An apparent inequality in the relative concentrations of carbohydrate and nitrogen in the apical meristem was observed in all treatments at the time of floral transition and is in support of the nutrient diversion hypothesis.

Biological Transport↗

PubMed2003

Exogenously applied jasmonic acid induces changes in apical meristem morphology of potato stolons.

Hooked apex stolons and initial swelling stolons of potato plants were treated with 3 x 10-8 mol l-1 jasmonic acid (JA) to study the effect of this compound on histology, cell expansion and tissue differentiation. In hooked apex stolons, JA application increased the meristem thickness and reduced the length of the leaf primordia, whereas in initial swelling stolons narrowing of the apical region, absence of leaf primordia and swelling of the subapical meristem were evident. Early vascular tissue differentiation was observed in response to JA treatment, especially of xylem elements from regions proximal to the tunic. Protoxylem elements, such as tracheal elements, were present with thin primary cell walls. The cell area was measured in two zones: zone I, central mother cells situated immediately under the tunic; and zone II, rib meristem cells. JA caused a four- and six-fold increase in cell area in both zones in hooked apex stolons and initial swelling stolons, respectively. Thus, tuber formation is concluded to occur as a consequence of increased cell expansion, a reduction in the length of leaf primordia, enlargement of meristems, and early vascular tissue differentiation.

Cell Differentiation↗

PubMed1998

The TERMINAL FLOWER2 (TFL2) gene controls the reproductive transition and meristem identity in Arabidopsis thaliana.

A new mutant of Arabidopsis thaliana that initiates flowering early and terminates the inflorescence with floral structures has been identified and named terminal flower2 (tfl2). While these phenotypes are similar to that of the terminal flower1 (tfl1) mutant, tfl2 mutant plants are also dwarfed in appearance, have reduced photoperiod sensitivity and have a more variable terminal flower structure. Under long-day and short-day growth conditions tfl1 tfl2 double mutants terminate the inflorescence without development of lateral flowers; thus, unlike tfl1 single mutants the double mutant inflorescence morphology is not affected by day length. The enhanced phenotype of the double mutant suggests that TFL2 acts in a developmental pathway distinct from TFL1. The complex nature of the tfl2 single mutant phenotype suggests that TFL2 has a regulatory role more global than that of TFL1. Double mutant analysis of tfl2 in combination with mutant alleles of the floral meristem identity genes LEAFY and APETALA1 demonstrates that TFL2 function influences developmental processes controlled by APETALA1, but not those regulated by LEAFY. Thus, the TFL2 gene product appears to have a dual role in regulating meristem activity, one being to regulate the meristem response to light signals affecting the development of the plant and the other being the maintenance of inflorescence meristem identity.

Arabidopsis↗

PubMed2006

Chemically forced dormancy termination mimics natural dormancy progression in potato tuber meristems by reducing ABA content and modifying expression of genes involved in regulating ABA synthesis and metabolism.

The length of potato tuber dormancy depends on both the genotype and the environmental conditions during growth and storage. Abscisic acid (ABA) has been shown to play a critical role in tuber dormancy control but the mechanisms regulating ABA content during dormancy, as well as the sites of ABA synthesis, and catabolism are unknown. Recently, a temporal correlation between changes in ABA content and certain ABA biosynthetic and catabolic genes has been reported in stored field tubers during physiological dormancy progression. However, the protracted length of natural dormancy progression complicated interpretation of these data. To address this issue, in this study the synthetic dormancy-terminating agent bromoethane (BE) was used to induce rapid and highly synchronous sprouting of dormant tubers. The endogenous ABA content of tuber meristems increased 2-fold 24 h after BE treatment and then declined dramatically. By 7 d post-treatment, meristem ABA content had declined by >80%. Exogenous [(3)H]ABA was readily metabolized by isolated meristems to phaseic and dihydrophaseic acids. BE treatment resulted in an almost 2-fold increase in the rate of ABA metabolism. A differential expression of both the StNCED and StCYP707A gene family members in meristems of BE-treated tubers is consistent with a regulatory role for StNCED2 and the StCYP707A1 and StCYP707A2 genes. The present results show that the changes in ABA content observed during tuber dormancy progression are the result of a dynamic equilibrium of ABA biosynthesis and degradation that increasingly favours catabolism as dormancy progresses.

Abscisic Acid↗

PubMed2001

The fasciated ear2 gene encodes a leucine-rich repeat receptor-like protein that regulates shoot meristem proliferation in maize.

The ability to initiate organs throughout the lifecycle is a unique feature of plant development that is executed by groups of stem cells called meristems. The balance between stem cell proliferation and organ initiation is carefully regulated and ensures that organs can be initiated in regular geometric patterns. To understand how this regulation is achieved, we isolated a novel mutant of maize, fasciated ear2 (fea2), which causes a massive overproliferation of the ear inflorescence meristem and a more modest effect on floral meristem size and organ number. We cloned the fea2 gene using transposon tagging, and it encodes a membrane localized leucine-rich repeat receptor-like protein that is most closely related to CLAVATA2 from Arabidopsis. These findings provide evidence that the CLAVATA pathway for regulation of meristem size is functionally conserved throughout the angiosperms. A possible connection of fea2 to the control of crop yields is discussed.

Amino Acid Sequence↗

PubMed2001

A TERMINAL FLOWER1-like gene from perennial ryegrass involved in floral transition and axillary meristem identity.

Control of flowering and the regulation of plant architecture have been thoroughly investigated in a number of well-studied dicot plants such as Arabidopsis, Antirrhinum, and tobacco. However, in many important monocot seed crops, molecular information on plant reproduction is still limited. To investigate the regulation of meristem identity and the control of floral transition in perennial ryegrass (Lolium perenne) we isolated a ryegrass TERMINAL FLOWER1-like gene, LpTFL1, and characterized it for its function in ryegrass flower development. Perennial ryegrass requires a cold treatment of at least 12 weeks to induce flowering. During this period a decrease in LpTFL1 message was detected in the ryegrass apex. However, upon subsequent induction with elevated temperatures and long-day photoperiods, LpTFL1 message levels increased and reached a maximum when the ryegrass apex has formed visible spikelets. Arabidopsis plants overexpressing LpTFL1 were significantly delayed in flowering and exhibited dramatic changes in architecture such as extensive lateral branching, increased growth of all vegetative organs, and a highly increased trichome production. Furthermore, overexpression of LpTFL1 was able to complement the phenotype of the severe tfl1-14 mutant of Arabidopsis. Analysis of the LpTFL1 promoter fused to the UidA gene in Arabidopsis revealed that the promoter is active in axillary meristems, but not the apical meristem. Therefore, we suggest that LpTFL1 is a repressor of flowering and a controller of axillary meristem identity in ryegrass.

Amino Acid Sequence↗

PubMed2003

The CUP-SHAPED COTYLEDON3 gene is required for boundary and shoot meristem formation in Arabidopsis.

From an enhancer trap screen for genes expressed in Arabidopsis embryos, we identified a gene expressed from the octant stage onward in the boundary between the two presumptive cotyledons and in a variety of postembryonic organ and meristem boundaries. This gene, CUP-SHAPED COTYLEDON3 (CUC3), encodes a putative NAC-domain transcription factor that is homologous with CUC1 and CUC2. Analysis of a CUC3 hypomorph and a putative cuc3 null mutant indicates that CUC3 function is partially redundant with that of CUC1 and CUC2 in the establishment of the cotyledon boundary and the shoot meristem, thus revealing an even higher degree of redundancy in this class of genes than was thought previously. The CUC3 expression pattern, the cuc3 phenotypes, and CUC3 expression in a series of shoot meristem mutants and transgenes suggest a primary role for CUC3 in the establishment of boundaries that contain cells with low proliferation and/or differentiation rates. The CUC-mediated establishment of such boundaries may be essential for the initiation of shoot meristems.

Arabidopsis↗

PubMed2004

HANABA TARANU is a GATA transcription factor that regulates shoot apical meristem and flower development in Arabidopsis.

We have isolated a new mutant, hanaba taranu (han), which affects both flower and shoot apical meristem (SAM) development in Arabidopsis thaliana. Mutants have fused sepals and reduced organ numbers in all four whorls, especially in the 2nd (petal) and 3rd (stamen) whorls. han meristems can become flatter or smaller than in the wild type. HAN encodes a GATA-3-like transcription factor with a single zinc finger domain. HAN is transcribed at the boundaries between the meristem and its newly initiated organ primordia and at the boundaries between different floral whorls. It is also expressed in vascular tissues, developing ovules and stamens, and in the embryo. han interacts strongly with clavata (clv) mutations (clv1, clv2, and clv3), resulting in highly fasciated SAMs, and we find that WUS expression is altered in han mutants from early embryogenesis. In addition, HAN is ectopically expressed both in clv1 and clv3 mutants. We propose that HAN is normally required for establishing organ boundaries in shoots and flowers and for controlling the number and position of WUS-expressing cells. Ectopic HAN expression causes growth retardation, aberrant cell division patterns, and loss of meristem activity, suggesting that HAN is involved in controlling cell proliferation and differentiation.

Amino Acid Sequence↗

PubMed2005

Regulation of WUSCHEL transcription in the stem cell niche of the Arabidopsis shoot meristem.

Pluripotent stem cells are localized in specialized microenvironments, called stem cell niches, where signals from surrounding cells maintain their undifferentiated status. In the Arabidopsis thaliana shoot meristem, the homeobox gene WUSCHEL (WUS) is expressed in the organizing center underneath the stem cells and integrates regulatory information from several pathways to define the boundaries of the stem cell niche. To investigate how these boundaries are precisely maintained within the proliferating cellular context of the shoot meristem, we analyzed the transcriptional control of the WUS gene. Our results show that the WUS promoter contains distinct regulatory regions that control tissue specificity and levels of transcription in a combinatorial manner. However, a 57-bp regulatory region is all that is required to control the boundaries of WUS transcription in the shoot meristem stem cell niche, and this activity can be further assigned to two adjacent short sequence motifs within this region. Our results indicate that the diverse regulatory pathways that control the stem cells in the shoot meristem converge at these two short sequence elements of the WUS promoter, suggesting that the integration of regulatory signals takes place at the level of a central transactivating complex.

Arabidopsis↗

PubMed2006

Analysis of the transcription factor WUSCHEL and its functional homologue in Antirrhinum reveals a potential mechanism for their roles in meristem maintenance.

One of the most significant features of plant development is the way in which it can be elaborated and modulated throughout the life of the plant, an ability that is conferred by meristems. The Arabidopsis thaliana WUSCHEL gene (WUS), which encodes a homeodomain transcription factor, is required to maintain the stem cells in the shoot apical meristem in an undifferentiated state. The mechanism by which WUS prevents the differentiation of stem cells is unknown. We have characterized a meristem maintenance mutant in Antirrhinum majus and shown that it arises from a defect in the WUS orthologue ROSULATA (ROA). Detailed characterization of a semidominant roa allele revealed an essential role for the conserved C-terminal domain. Expression of either ROA or WUS lacking this domain causes a failure of meristem maintenance. The conserved domain mediates an interaction between WUS and two members of a small family of corepressor-like proteins in Arabidopsis. Our results suggest that WUS functions by recruiting transcriptional corepressors to repress target genes that promote differentiation, thereby ensuring stem cell maintenance.

Alleles↗

PubMed2006

Dynamic and compensatory responses of Arabidopsis shoot and floral meristems to CLV3 signaling.

In Arabidopsis thaliana, the stem cell population of the shoot system is controlled by regulatory circuitry involving the WUSCHEL (WUS) and CLAVATA (CLV1-3) genes. WUS signals from the organizing center (OC) to promote stem cell fate at the meristem apex. Stem cells express the secreted peptide CLV3 that activates a signal transduction cascade to restrict WUS expression, thus providing a feedback mechanism. Stem cell homeostasis is proposed to be achieved by balancing these signals. We tested the dynamics of CLV3 signaling using an inducible gene expression system. We show here that increasing the CLV3 signal can very rapidly repress WUS expression during development, which in turn causes a fast reduction of CLV3 expression. We demonstrate that increased CLV3 signaling restricts meristem growth and promotes allocation of peripheral meristem cells into organ primordia. In addition, we extend the current model for stem cell control by showing that meristem homeostasis tolerates variation in CLV3 levels over a 10-fold range and that high-level CLV3 signaling can be partially compensated with time, indicating that the level of CLV3 expression communicates only limited information on stem cell number to the underlying OC cells.

Arabidopsis↗

PubMed1999

Interactions between jointless and wild-type tomato tissues during development of the pedicel abscission zone and the inflorescence meristem.

The jointless mutation of tomato results in the formation of flower pedicels that lack an abscission zone and inflorescence meristems that revert to vegetative growth. We have analyzed periclinal chimeras and mericlinal sectors of jointless and wild-type tissue to determine how cells in different meristem layers (L1, L2, and L3) and their derivatives interact during these two developmental processes. Cells in the inner meristem layer, L3, alone determined whether the meristem maintained the inflorescence state or reverted to vegetative growth. Moreover, L3 derivatives determined whether a functional pedicel abscission zone formed. Limited and disorganized autonomous development of wild-type L2-derived cells occurred when they overlay mutant tissue. Adjacent mutant and wild-type L3-derived tissues in pedicels developed autonomously, indicating little or no lateral communication. Only the outermost L3-derived cells within the pedicel were capable of orchestrating normal pedicel development in overlying tissues, revealing the special status of those cells as coordinators of development for L1- and L2-derived cells, whereas the innermost L3-derived cells developed autonomously but did not influence the development of other cells.

Chimera↗