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At least 19 recordsLinked to original sources
PubMed2006

The rice heterochronic gene SUPERNUMERARY BRACT regulates the transition from spikelet meristem to floral meristem.

Regulating the transition of meristem identity is a critical step in reproductive development. After the shoot apical meristem (SAM) acquires inflorescence meristem identity, it goes through a sequential transition to second- and higher-order meristems that can eventually give rise to floral organs. Despite ample information on the molecular mechanisms that control the transition from SAM to inflorescence meristems, little is known about the mechanism for inflorescence development, especially in monocots. Here, we report the identification of the SUPERNUMERARY BRACT (SNB) gene controlling the transition from spikelet meristem to floral meristem and the floral organ development. This gene encodes a putative transcription factor carrying two AP2 domains. The SNB:GFP fusion protein is localized to the nucleus. SNB is expressed in all the examined tissues, but most strongly in the newly emerging spikelet meristems. In SNB knockout plants, the transition from spikelet meristems to floral meristems is delayed, resulting in the production of multiple rudimentary glumes in an alternative phyllotaxy. The development of additional bracts interferes with subsequent floral architecture. In some spikelets, the empty glumes and lodicules are transformed into lemma/palea-like organs. Occasionally, the number of stamens and carpels is altered and an ectopic floret occurs in the axil of the rachilla. These phenotypes suggest that snb is a heterochronic mutant, affecting the phase transition of spikelet meristems, the pattern formation of floral organs and spikelet meristem determinancy.

Amino Acid Sequence↗
PubMed2004

The ULTRAPETALA1 gene functions early in Arabidopsis development to restrict shoot apical meristem activity and acts through WUSCHEL to regulate floral meristem determinacy.

Shoot and floral meristem activity in higher plants is controlled by complex signaling networks consisting of positive and negative regulators. The Arabidopsis ULTRAPETALA1 (ULT1) gene has been shown to act as a negative regulator of meristem cell accumulation in inflorescence and floral meristems, as loss-of-function ult1 mutations cause inflorescence meristem enlargement, the production of extra flowers and floral organs, and a decrease in floral meristem determinacy. To investigate whether ULT1 functions in known meristem regulatory pathways, we generated double mutants between ult1 alleles and null alleles of the meristem-promoting genes SHOOTMERISTEMLESS (STM) and WUSCHEL (WUS). We found that, although the ult1 alleles have no detectable embryonic or vegetative phenotypes, ult1 mutations restored extensive organ-forming capability to stm null mutants after germination and increased leaf and floral organ production in stm partial loss-of-function mutants. Mutations in ULT1 also partially suppressed the wus shoot and floral meristem phenotypes. However, wus was epistatic to ult1 in the center of the flower, and WUS transcriptional repression was delayed in ult1 floral meristems. Our results show that during the majority of the Arabidopsis life cycle, ULT1 acts oppositely to STM and WUS in maintaining meristem activity and functions in a separate genetic pathway. However, ULT1 negatively regulates WUS to establish floral meristem determinacy, acting through the WUS-AG temporal feedback loop.

Arabidopsis↗
PubMed1996

The SHOOT MERISTEMLESS gene is required for maintenance of undifferentiated cells in Arabidopsis shoot and floral meristems and acts at a different regulatory level than the meristem genes WUSCHEL and ZWILLE.

The function of the SHOOT MERISTEMLESS (STM) gene in shoot and floral meristems throughout Arabidopsis development has been analyzed. The results show that STM plays a major role in maintaining shoot and floral meristems. In an allelic series of stm mutants the shoot meristem was either reduced or completely absent in mature embryos and mutant seedling cotyledons showed partial fusion, indicating that the STM gene affects embryonic shoot meristem development and spacing of cotyledons. Postembryonically, stm mutants initiated adventitious shoot development at a position corresponding to the shoot meristem in wild-type. Repetitively initiated defective mutant shoot and floral meristems were consumed during primordia formation and typically terminated prematurely in fused ectopic primordia, indicating that STM is required for continuous shoot and floral meristem function. Analogous defects were observed in stm embryonic and postembryonic development suggesting that similar mechanisms are employed in embryonic and postembryonic organ primordia initiation. Allelic combination suggest different thresholds for STM requirement during plant development. STM requirement could not be bypassed by standard growth factor regimes or by shoot regeneration from calli. The results suggest that STM functions by preventing incorporation of cells in the meristem center into differentiating organ primordia and that this role can completely account for all defects observed in stm mutants. Mutations in the WUSCHEL (WUS) and ZWILLE (ZLL) genes result in defective organization and premature termination of shoot meristems. Genetic interactions between STM, WUS and ZLL were analyzed and the results indicate that STM acts upstream of WUS and ZLL. Therefore, while STM appears to function in keeping central meristem cells undifferentiated, WUS and ZLL seem to be subsequently required for proper function of these cells.

Alleles↗
PubMed2000

Mapping meristem respiration of Prunus persica (L.) Batsch seedlings: potential respiration of the meristems, O2 diffusional constraints and combined effects on root growth.

Root system architecture partially results from meristem activities, which themselves depend on endogenous and environmental factors, such as O2 depletion. In this study, meristem respiration and growth was measured in the root systems of three Prunus persica (L.) Batsch seedlings. The spatial distribution of meristem respiration within the root system was described, and the relationship between the respiration rates and meristem radii was analysed, using a model of radial O2 diffusion and consumption within the root. Histological observations were also used to help interpret the results. Respiration rates were linearly correlated to the root growth rates (rho 2 = 0.9). Respiration reached values greater than 3.5 x 10(-13) mol O2 s-1 for active meristems. The taproot meristem consumed more O2 than the rest of the entire root system meristems. Similarly, the first order lateral meristems used more O2 than the second order ones. A near hyperbolic relationship between respiration rates and meristem radii was observed. This can be explained by a model of radial O2 diffusion and consumption within the root. Therefore, only one maximum potential respiration rate and one O2 diffusion coefficient was estimated for all the meristems.

Cell Respiration↗
PubMed1998

Expression of CDC2Zm and KNOTTED1 during in-vitro axillary shoot meristem proliferation and adventitious shoot meristem formation in maize (Zea mays L.) and barley (Hordeum vulgare L.).

Expression of CDC2Zm and KNOTTED1 (KN1) in maize (Zea mays L.) and their cross-reacting proteins in barley (Hordeum vulgare L.) was studied using immunolocalization during in-vitro axillary shoot meristem proliferation and adventitious shoot meristem formation. Expression of CDC2Zm, a protein involved in cell division, roughly correlated with in-vitro cell proliferation and in the meristematic domes CDC2Zm expression was triggered during in-vitro proliferation. Analysis of the expression of KN1, a protein necessary for maintenance of the shoot meristem, showed that KN1 or KN1-homologue(s) expression was retained in meristematic cells during in-vitro proliferation of axillary shoot meristems. Multiple adventitious shoot meristems appeared to form directly from the KN1- or KN1 homologue(s)-expressing meristematic cells in the invitro proliferating meristematic domes. However, unlike Arabidopsis (Arabidopsis thaliana) and tobacco (Nicotiana tabacum) leaves ectopically expressing KN1 (G. Chuck et al., 1996 Plant Cell 8: 1277-1289; N. Sinha et al., 1993 Genes Dev. 7: 787-797), transgenic maize leaves over-expressing KN1 were unable to initiate adventitious shoot meristems on their surfaces either in planta or in vitro. Therefore, expression of KN1 is not the sole triggering factor responsible for inducing adventitious shoot meristem formation from in-vitro proliferating axillary shoot meristems in maize. Our results show that genes critical to cell division and plant development have utility in defining in-vitro plant morphogenesis at the molecular level and, in combination with transformation technologies, will be powerful tools in identifying the fundamental molecular and-or genetic triggering factor(s) responsible for reprogramming of plant cells during plant morphogenesis in-vitro.

Antibodies↗
PubMed1992

The internal meristem layer (L3) determines floral meristem size and carpel number in tomato periclinal chimeras.

Cell-cell interactions are important during plant development. We have generated periclinal chimeras between plants that differ in the number of carpels per flower to determine the roles of cells occupying specific positions in the floral meristem in determining the number of carpels initiated. Intraspecific chimeras were generated between tomato (Lycopersicon esculentum) expressing the mutation fasciated, which causes an increased number of floral organs per whorl, and tomato wild type for fasciated. Interspecific chimeras were generated between tomato and L. peruvianum, which differ in number of carpels per flower. In both sets of chimeras, carpel number as well as the size of the floral meristem during carpel initiation were not determined by the genotype of cells in the outer two layers of the meristem (L1 and L2) but were determined by the genotype of cells occupying the inner layer (L3) of the meristem. We concluded from these experiments that during floral organ initiation, cells in certain layers of the meristem respond to information supplied to them from other cells in the meristem.

Chimera↗
PubMed2002

PROLIFERATING INFLORESCENCE MERISTEM, a MADS-box gene that regulates floral meristem identity in pea.

SQUAMOSA and APETALA1 are floral meristem identity genes from snapdragon (Antirrhinum majus) and Arabidopsis, respectively. Here, we characterize the floral meristem identity mutation proliferating inflorescence meristem (pim) from pea (Pisum sativum) and show that it corresponds to a defect in the PEAM4 gene, a homolog of SQUAMOSA and APETALA1. The PEAM4 coding region was deleted in the pim-1 allele, and this deletion cosegregated with the pim-1 mutant phenotype. The pim-2 allele carried a nucleotide substitution at a predicted 5' splice site that resulted in mis-splicing of pim-2 mRNA. PCR products corresponding to unspliced and exon-skipped mRNA species were observed. The pim-1 and pim-2 mutations delayed floral meristem specification and altered floral morphology significantly but had no observable effect on vegetative development. These floral-specific mutant phenotypes and the restriction of PIM gene expression to flowers contrast with other known floral meristem genes in pea that additionally affect vegetative development. The identification of PIM provides an opportunity to compare pathways to flowering in species with different inflorescence architectures.

Base Sequence↗
PubMed2003

FRIZZY PANICLE is required to prevent the formation of axillary meristems and to establish floral meristem identity in rice spikelets.

Inflorescences of grass species have a distinct morphology in which florets are grouped in compact branches called spikelets. Although many studies have shown that the molecular and genetic mechanisms that control floret organ formation are conserved between monocots and dicots, little is known about the genetic pathway leading to spikelet formation. In the frizzy panicle (fzp) mutant of rice, the formation of florets is replaced by sequential rounds of branching. Detailed analyses revealed that several rudimentary glumes are formed in each ectopic branch, indicating that meristems acquire spikelet identity. However, instead of proceeding to floret formation, axillary meristems are formed in the axils of rudimentary glumes and they either arrest or develop into branches of higher order. The fzp mutant phenotype suggests that FZP is required to prevent the formation of axillary meristems within the spikelet meristem and permit the subsequent establishment of floral meristem identity. The FZP gene was isolated by transposon tagging. FZP encodes an ERF transcription factor and is the rice ortholog of the maize BD1 gene. Consistent with observations from phenotypic analyses, FZP expression was found to be restricted to the time of rudimentary glumes differentiation in a half-ring domain at the base of which the rudimentary glume primordium emerged.

Amino Acid Sequence↗
PubMed1996

The no apical meristem gene of Petunia is required for pattern formation in embryos and flowers and is expressed at meristem and primordia boundaries.

Petunia embryos carrying the no apical meristem (nam) mutation fail to develop a shoot apical meristem. Occasional shoots on nam- seedlings bear flowers that develop ten instead of five primordia in the second whorl. Double mutants with the homeotic gene green petals show that nam acts independently of organ identify in whorl 2 and now also affects primordium number in whorl 3. The nam gene was isolated by transposon tagging. The encoded protein shares a conserved N-terminal domain with several other proteins of unknown function and thus represents a novel class of proteins. Strikingly, nam mRNA accumulates in cells at the boundaries of meristems and primordia. These data indicate a role for nam in determining positions of meristems and primordia.

Alleles↗
PubMedDate not supplied

KNOX homeobox genes potentially have similar function in both diploid unicellular and multicellular meristems, but not in haploid meristems.

Members of the class 1 knotted-like homeobox (KNOX) gene family are important regulators of shoot apical meristem development in angiosperms. To determine whether they function similarly in seedless plants, three KNOX genes (two class 1 genes and one class 2 gene) from the fern Ceratopteris richardii were characterized. Expression of both class 1 genes was detected in the shoot apical cell, leaf primordia, marginal part of the leaves, and vascular bundles by in situ hybridization, a pattern that closely resembles that of class 1 KNOX genes in angiosperms with compound leaves. The fern class 2 gene was expressed in all sporophyte tissues examined, which is characteristic of class 2 gene expression in angiosperms. All three CRKNOX genes were not detected in gametophyte tissues by RNA gel blot analysis. Arabidopsis plants overexpressing the fern class 1 genes resembled plants that overexpress seed plant class 1 KNOX genes in leaf morphology. Ectopic expression of the class 2 gene in Arabidopsis did not result in any unusual phenotypes. Taken together with phylogenetic analysis, our results suggest that (a) the class 1 and 2 KNOX genes diverged prior to the divergence of fern and seed plant lineages, (b) the class 1 KNOX genes function similarly in seed plant and fern sporophyte meristem development despite their differences in structure, (c) KNOX gene expression is not required for the development of the fern gametophyte, and (d) the sporophyte and gametophyte meristems of ferns are not regulated by the same developmental mechanisms at the molecular level.

Arabidopsis↗
PubMed1992

A meristem-related gene from tomato encodes a dUTPase: analysis of expression in vegetative and floral meristems.

A meristem-specific gene coding for deoxyuridine triphosphatase (EC 3.6.1.23) (dUTPase) in tomato was isolated, and its developmental expression in vegetative and floral apices was monitored. An 18-kD polypeptide, P18, was isolated as a consequence of its accumulation in arrested floral meristems of anantha mutant plants. The corresponding cDNA isolated from an expression library exhibited a 40 to 60% similarity with the pseudoprotease sequences of poxviruses, genes that have been suggested to encode dUTPases. Enzymatic tests and conservation of peptide motifs common to bacterial and viral genes verified that the P18 cDNA clone indeed represents a eukaryotic dUTPase. Immunogold localization and in situ hybridization experiments showed that polypeptides and transcripts of dUTPase are maintained at high levels in apical meristematic cells of vegetative and floral meristems. dUTPase gene activity is also high in the potentially meristematic cells of the provascular and vascular system. Its expression is lower in the immediate parenchymal derivatives of the apical meristematic cells, and this downregulation marks, perhaps, the transition from totipotency to the first differentiated state.

Amino Acid Sequence↗
PubMed1999

The Arabidopsis thaliana MERISTEM LAYER 1 promoter specifies epidermal expression in meristems and young primordia.

The Arabidopsis thaliana MERISTEM LAYER 1 (ATML1) gene is expressed in the epidermis of developing embryos and shoot meristems. To identify regulatory sequences necessary for epidermis-specific expression, three fusions of overlapping ATML1 genomic sequences to the GUS reporter gene were introduced into Arabidopsis plants. All fusion genes conferred epidermis-specific expression of both GUS mRNA and protein activity but varied in both the timing and relative levels of expression, suggesting partial redundancy of ATML1 regulatory elements. This study defines L1-specific regulatory sequences that are sufficient to direct foreign gene expression in a layer-specific manner.

Arabidopsis↗
PubMed2001

Autoreproductive cells and plant meristem construction: the case of the tomato cap meristem.

Root apical meristems are composed of two zones in which either formative or proliferative cell divisions occur. Within the formative zone, autoreproductive initial cells (a-cells) occupy distinctive locations. By means of graph-L-systems, the behavior of one such type of a-cells has been investigated, with particular reference to root caps within the developing primordia of lateral roots of Lycopersicon esculentum cultivated in vitro. Here, the a-cells constitute the "protoderm initials", cells which are found also in the root cap of many angiosperm species. A set of cuboidal (i.e., six-sided) a-cells develops early in the ontogeny of a lateral-root primordium. Then, according to both anatomical observations and theoretical simulations obtained by the application of graph-L-systems, sequential production of descendents from each a-cell leads to the formation of a new autoreproductive cell (a), a cap columella initial (c), and two mother cells (e and f) whose respective descendents differentiate as root epidermis and cap flank cells. In this graph-L-system, there is specification of the location of sister cells with respect to the three orthogonal directions of a cuboidal. In the early stage of root cap formation, only a few rounds of these formative cell divisions by each a-cell and its four types of descendents are required to provide the basic set of cells necessary for full cap development. After the lateral root emerges from the parent root, there may be a temporary cessation of the formative divisions of the a-cells which give rise to columella initials. Columella production is then supported entirely by its own independent set of autoreproductive c-initials. At the same time, division of the autoreproductive protoderm initial cell is directed towards maintaining the cap flank and the epidermal cell files. The regulation of the types of formative division by the a-cell may be represented by means of a division counter which may be specific for a given species.

Algorithms↗
PubMed2002

The indeterminate floral apex1 gene regulates meristem determinacy and identity in the maize inflorescence.

Meristems may be determinate or indeterminate. In maize, the indeterminate inflorescence meristem produces three types of determinate meristems: spikelet pair, spikelet and floral meristems. These meristems are defined by their position and their products. We have discovered a gene in maize, indeterminate floral apex1 (ifa1) that regulates meristem determinacy. The defect found in ifa1 mutants is specific to meristems and does not affect lateral organs. In ifa1 mutants, the determinate meristems become less determinate. The spikelet pair meristem initiates more than a pair of spikelets and the spikelet meristem initiates more than the normal two flowers. The floral meristem initiates all organs correctly, but the ovule primordium, the terminal product of the floral meristem, enlarges and proliferates, expressing both meristem and ovule marker genes. A role for ifa1 in meristem identity in addition to meristem determinacy was revealed by double mutant analysis. In zea agamous1 (zag1) ifa1 double mutants, the female floral meristem converts to a branch meristem whereas the male floral meristem converts to a spikelet meristem. In indeterminate spikelet1 (ids1) ifa1 double mutants, female spikelet meristems convert to branch meristems and male spikelet meristems convert to spikelet pair meristems. The double mutant phenotypes suggest that the specification of meristems in the maize inflorescence involves distinct steps in an integrated process.

Gene Expression Regulation, Plant↗
PubMed2001

barren inflorescence2 regulates axillary meristem development in the maize inflorescence.

Organogenesis in plants is controlled by meristems. Shoot apical meristems form at the apex of the plant and produce leaf primordia on their flanks. Axillary meristems, which form in the axils of leaf primordia, give rise to branches and flowers and therefore play a critical role in plant architecture and reproduction. To understand how axillary meristems are initiated and maintained, we characterized the barren inflorescence2 mutant, which affects axillary meristems in the maize inflorescence. Scanning electron microscopy, histology and RNA in situ hybridization using knotted1 as a marker for meristematic tissue show that barren inflorescence2 mutants make fewer branches owing to a defect in branch meristem initiation. The construction of the double mutant between barren inflorescence2 and tasselsheath reveals that the function of barren inflorescence2 is specific to the formation of branch meristems rather than bract leaf primordia. Normal maize inflorescences sequentially produce three types of axillary meristem: branch meristem, spikelet meristem and floral meristem. Introgression of the barren inflorescence2 mutant into genetic backgrounds in which the phenotype was weaker illustrates additional roles of barren inflorescence2 in these axillary meristems. Branch, spikelet and floral meristems that form in these lines are defective, resulting in the production of fewer floral structures. Because the defects involve the number of organs produced at each stage of development, we conclude that barren inflorescence2 is required for maintenance of all types of axillary meristem in the inflorescence. This defect allows us to infer the sequence of events that takes place during maize inflorescence development. Furthermore, the defect in branch meristem formation provides insight into the role of knotted1 and barren inflorescence2 in axillary meristem initiation.

Chromosome Mapping↗
PubMed2003

Combinatorial control of meristem identity in maize inflorescences.

The architecture of maize inflorescences, the male tassel and the female ear, is defined by a series of reiterative branching events. The inflorescence meristem initiates spikelet pair meristems. These in turn initiate spikelet meristems which finally produce the floret meristems. After initiating one meristem, the spikelet pair and spikelet meristem convert into spikelet and floret meristems, respectively. The phenotype of reversed germ orientation1 (rgo1) mutants is the production of an increased number of floret meristems by each spikelet meristem. The visible phenotypes include increased numbers of flowers in tassel and ear spikelets, disrupted rowing in the ear, fused kernels, and kernels with embryos facing the base of the ear, the opposite orientation observed in wild-type ears. rgo1 behaves as single recessive mutant. indeterminate spikelet1 (ids1) is an unlinked recessive mutant that has a similar phenotype to rgo1. Plants heterozygous for both rgo1 and ids1 exhibit nonallelic noncomplementation; these mutants fail to complement each other. Plants homozygous for both mutations have more severe phenotypes than either of the single mutants; the progression of meristem identities is retarded and sometimes even reversed. In addition, in rgo1; ids1 double mutants extra branching is observed in spikelet pair meristems, a meristem that is not affected by mutants of either gene individually. These data suggest a model for control of meristem identity and determinacy in which the progress through meristem identities is mediated by a dosage-sensitive pathway. This pathway is combinatorially controlled by at least two genes that have overlapping functions.

Crosses, Genetic↗
PubMed2005

JOINTLESS suppresses sympodial identity in inflorescence meristems of tomato.

Unlike monopodial plants, in which flowering terminates growth of a shoot, plants exhibiting sympodial shoot architecture maintain the potential for indeterminate growth even after converting to floral development. This vegetative indeterminacy is conferred by a special type of axillary meristem, the sympodial meristem, which exhibits precocious but determinate growth. The reiterative formation of sympodial meristems as the plant grows results in a shoot composed of a series of modules, each consisting of a limited number of vegetative nodes and terminated by a flower or inflorescence. To determine how sympodial meristems differ from other shoot meristems, we examined interactions between mutations that affect various shoot meristem types in tomato (Lycopersicon esculentum Mill.). Analysis of double mutant combinations of jointless, lateral suppressor, self-pruning, blind, and anantha showed that sympodial meristems share regulatory features with inflorescence meristems. Genetic studies on the jointless mutation implicated this gene in suppressing sympodial meristem fate in the inflorescence. As this mutation has a second phenotype, the elimination of the pedicel abscission zone, we examined the expression pattern of JOINTLESS to test whether pedicel development is involved in directing shoot architecture. We found that this MADS box gene is expressed in a variety of shoot meristems, including inflorescence, floral, sympodial, and axillary meristems, as well as in early staged floral organs, in sporogenous tissues of anthers, and in ovules. Lack of expression in developing pedicels indicates abscission zone development does not rely on JOINTLESS transcription in the differentiating cells. We conclude that the primary role of JOINTLESS is to suppress sympodial meristem identity in inflorescence meristems.

Flowers↗