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At least 811 records · Page 45Linked to original sources

PubMed2001

A Brassica oleracea gene expressed in a variety-specific manner may encode a novel plant transmembrane receptor.

The species Brassica oleracea includes several agricultural varieties characterized by the proliferation of different types of meristems. Using a combination of subtractive hybridization and PCR (polymerase chain reaction) techniques we have identified several genes which are expressed in the reproductive meristems of the cauliflower curd (B. oleracea var. botrytis) but not in the vegetative meristems of Brussels sprouts (B. oleracea var. gemmifera) axillary buds. One of the cloned genes, termed CCE1 (CAULIFLOWER CURD EXPRESSION 1) shows specific expression in the botrytis variety. Preferential expression takes place in this variety in the meristems of the curd and in the stem throughout the vegetative and reproductive stages of plant growth. CCE1 transcripts are not detected in any of the organs of other B. oleracea varieties analyzed. Based on the nucleotide sequence of a cDNA encompassing the complete coding region, we predict that this gene encodes a transmembrane protein, with three transmembrane domains. The deduced amino acid sequence includes motifs conserved in G-protein-coupled receptors (GPCRs) from yeast and animal species. Our results suggest that the cloned gene encodes a protein belonging to a new, so far unidentified, family of transmembrane receptors in plants. The expression pattern of the gene suggests that the receptor may be involved in the control of meristem development/arrest that takes place in cauliflower.

Amino Acid Sequence↗

PubMed1997

Expression of cell cycle genes during Sesbania rostrata stem nodule development.

Upon infection of Sesbania rostrata with Azorhizobium caulinodans, nodules are formed on roots and stems. Stem nodules develop from abundantly distributed dormant root primordia. To acquire more insight into the meristem organization during stem nodule development, the expression patterns of a mitotic B1-type cyclin gene (Sesro; CycB1;1), a cyclin-dependent kinase gene (Cdc-2-1Sr), and a histone H4 gene (H4-1Sr) of S. rostrata were followed by in situ hybridization. Cdc2-1Sr transcripts were found in all cells of uninfected and infected root primordia. In uninfected root primordia, Sesro;CycB1;1 transcripts were detected in a few cells of the apical root meristem whereas H4-1Sr transcripts were abundant in this region. Interestingly, after inoculation with A. caulinodans, H4-1Sr transcripts disappeared in the root meristem and a patchy pattern of Sesro;CycB1;1 and H4-1Sr expression appeared in the cortex of the root primordium, reflecting the formation of globular nodule primordia. When bacterial invasion started, a distal nodule meristem was delimited wherein Sesro;CycB1;1 and H4-1Sr expression was concentrated. Approximately 1 week after inoculation, meristem activity ceased, indicated by the loss of Sesro;CycB1;1 and H4-1Sr expression.

Amino Acid Sequence↗

PubMed2004

Roles for Class III HD-Zip and KANADI genes in Arabidopsis root development.

Meristems within the plant body differ in their structure and the patterns and identities of organs they produce. Despite these differences, it is becoming apparent that shoot and root apical and vascular meristems share significant gene expression patterns. Class III HD-Zip genes are required for the formation of a functional shoot apical meristem. In addition, Class III HD-Zip and KANADI genes function in patterning lateral organs and vascular bundles produced from the shoot apical and vascular meristems, respectively. We utilize both gain- and loss-of-function mutants and gene expression patterns to analyze the function of Class III HD-Zip and KANADI genes in Arabidopsis roots. Here we show that both Class III HD-Zip and KANADI genes play roles in the ontogeny of lateral roots and suggest that Class III HD-Zip gene activity is required for meristematic activity in the pericycle analogous to its requirement in the shoot apical meristem.

Arabidopsis↗

PubMed1997

Experimental Analysis of Tassel Development in the Maize Mutant Tassel Seed 6.

The maize (Zea mays L.) mutation Tassel seed 6 (Ts6) disrupts both sex determination in the tassel and the pattern of branching in inflorescences. This results in the formation of supernumerary florets in tassels and ears and in the development of pistils in tassel florets where they are normally aborted. A developmental analysis indicated that extra florets in Ts6 inflorescences are most likely the result of delayed determinacy in spikelet meristems, which then initiate additional floret meristems rather than initiating floral organs as in wild type. I have used culturing experiments to assay whether delayed determinacy of Ts6 mutant tassels is reflected in an altered timing of specific determination events. Length of the tassel was used as a developmental marker. These experiments showed that although Ts6 tassels elongate much more slowly than wild type, both mutant and wild-type tassels gained the ability to form flowers with organs of normal morphology in culture at the same time. In situ hybridization patterns of expression of the maize gene Kn, which is normally expressed in shoot meristems and not in determinate lateral organs, confirmed that additional meristems, rather than lateral organs, are initiated by spikelet meristems in Ts6 tassels.

Journal Article↗

PubMed1981

Effect of auxin on acropetal auxin transport in roots of corn.

Acropetal [(14)C]indoleacetic acid (IAA) transport was investigated in roots of corn. At least 40 to 50% of this movement is dependent on activities in the root apex. Selective excision of various populations of cells comprising the root apex, e.g. the root cap, quiescent center, or proximal meristem show that the proximal meristem is the critical region in the apex with regard to influencing IAA movement. The quiescent center has no influence and the root cap has only a minor effect. Excision and replacement of the proximal meristem with an exogenous supply of 10(-8) to 10(-9) molar IAA prevents the reduction in acropetal IAA transport which would normally occur in the absence of this meristem. Substituting 10(-9) molar IAA for the excised root cap brings about a significant increase in the amount of IAA moved acropetally, as compared to intact roots with the root cap still in place. From this and previous work, it is concluded that IAA synthesis occurring in the proximal meristem stimulates the movement of IAA from the basal to apical end of the root.

Journal Article↗

PubMed1997

FPF1 promotes flowering in Arabidopsis.

We have characterized the gene flowering promoting factor1 (FPF1), which is expressed in apical meristems immediately after the photoperiodic induction of flowering in the long-day plants mustard and Arabidopsis. In early transition stages, expression is only detectable in the peripheral zone of apical meristems; however, later on, it can also be found in floral meristems and in axillary meristems that form secondary inflorescences. The FPF1 gene encodes a 12.6-kD protein that has no homology to any previously identified protein of known function. Constitutive expression of the gene in Arabidopsis under control of the cauliflower mosaic virus 35S promoter resulted in a dominant heritable trait of early flowering under both short- and long-day conditions. Treatments with gibberellin (GA) and paclobutrazol, a GA biosynthesis inhibitor, as well as crosses with GA-deficient mutants indicate that FPF1 is involved in a GA-dependent signaling pathway and modulates a GA response in apical meristems during the transition to flowering.

Amino Acid Sequence↗

PubMed2005

thick tassel dwarf1 encodes a putative maize ortholog of the Arabidopsis CLAVATA1 leucine-rich repeat receptor-like kinase.

Development in higher plants depends on the activity of meristems, formative regions that continuously initiate new organs at their flanks. Meristems must maintain a balance between stem cell renewal and organ initiation. In fasciated mutants, organ initiation fails to keep pace with meristem proliferation. The thick tassel dwarf1 (td1) mutation of maize affects both male and female inflorescence development. The female inflorescence, which results in the ear, is fasciated, with extra rows of kernels. The male inflorescence, or tassel, shows an increase in spikelet density. Floral meristems are also affected in td1 mutants; for example, male florets have an increase in stamen number. These results suggest that td1 functions in the inflorescence to limit meristem size. In addition, td1 mutants are slightly shorter than normal siblings, indicating that td1 also plays a role in vegetative development. td1 encodes a leucine-rich repeat receptor-like kinase (LRR-RLK) that is a putative ortholog of the Arabidopsis CLAVATA1 protein. These results complement previous work showing that fasciated ear2 encodes a CLAVATA2-like protein, and suggest that the CLAVATA signaling pathway is conserved in monocots. td1 maps in the vicinity of quantitative trait loci that affect seed row number, spikelet density and plant height. We discuss the possible selection pressures on td1 during maize domestication.

Amino Acid Sequence↗

PubMed1999

A petunia MADS box gene involved in the transition from vegetative to reproductive development.

We have identified a novel petunia MADS box gene, PETUNIA FLOWERING GENE (PFG), which is involved in the transition from vegetative to reproductive development. PFG is expressed in the entire plant except stamens, roots and seedlings. Highest expression levels of PFG are found in vegetative and inflorescence meristems. Inhibition of PFG expression in transgenic plants, using a cosuppression strategy, resulted in a unique nonflowering phenotype. Homozygous pfg cosuppression plants are blocked in the formation of inflorescences and maintain vegetative growth. In these mutants, the expression of both PFG and the MADS box gene FLORAL BINDING PROTEIN26 (FBP26), the putative petunia homolog of SQUAMOSA from Antirrhinum, are down-regulated. In hemizygous pfg cosuppression plants initially a few flowers are formed, after which the meristem reverts to the vegetative phase. This reverted phenotype suggests that PFG, besides being required for floral transition, is also required to maintain the reproductive identity after this transition. The position of PFG in the hierarchy of genes controlling floral meristem development was investigated using a double mutant of the floral meristem identity mutant aberrant leaf and flower (alf) and the pfg cosuppression mutant. This analysis revealed that the pfg cosuppression phenotype is epistatic to the alf mutant phenotype, indicating that PFG acts early in the transition to flowering. These results suggest that the petunia MADS box gene, PFG, functions as an inflorescence meristem identity gene required for the transition of the vegetative shoot apex to the reproductive phase and the maintenance of reproductive identity.

Amino Acid Sequence↗

PubMed1999

The PINHEAD/ZWILLE gene acts pleiotropically in Arabidopsis development and has overlapping functions with the ARGONAUTE1 gene.

Several lines of evidence indicate that the adaxial leaf domain possesses a unique competence to form shoot apical meristems. Factors required for this competence are expected to cause a defect in shoot apical meristem formation when inactivated and to be expressed or active preferentially in the adaxial leaf domain. PINHEAD, a member of a family of proteins that includes the translation factor eIF2C, is required for reliable formation of primary and axillary shoot apical meristems. In addition to high-level expression in the vasculature, we find that low-level PINHEAD expression defines a novel domain of positional identity in the plant. This domain consists of adaxial leaf primordia and the meristem. These findings suggest that the PINHEAD gene product may be a component of a hypothetical meristem forming competence factor. We also describe defects in floral organ number and shape, as well as aberrant embryo and ovule development associated with pinhead mutants, thus elaborating on the role of PINHEAD in Arabidopsis development. In addition, we find that embryos doubly mutant for PINHEAD and ARGONAUTE1, a related, ubiquitously expressed family member, fail to progress to bilateral symmetry and do not accumulate the SHOOT MERISTEMLESS protein. Therefore PINHEAD and ARGONAUTE1 together act to allow wild-type growth and gene expression patterns during embryogenesis.

Alleles↗

PubMed1997

Relationship between cell proliferation and transition to elongation in plant roots.

Relationship between two main growth processes, cell proliferation and elongation, is reviewed. In literature, meristem and elongation zones are discriminated according to: increase in relative growth rate, change in cell shape, cessation of mitoses, and change in cell structure, vacuolation in particular. Relative growth rate is almost constant along the meristem and increases sharply in the course of cell transition to elongation. The transition of cells to elongation cannot be considered as a continuation of meristematic growth after the cessation of divisions. The most valid criterion of the cell transition to elongation is a sharp rise in relative growth rate, ratherthan change in cell shape (form factor). In the growing roottip, there aretwo regions of more active accumulation of proteins. The first is associated with the fastest cell proliferation while the second corresponds to enhanced cell elongation. The results of experiments with X-irradiation and cytostatic drugs suggest that cell transition to elongation is independent of cell proliferation and is regulated by the processes determining the life-span of cells in the meristem. The rate of cell transition to elongation is controlled by the processes determining both the life-span of cells in the meristem and the rate of cell proliferation. For most meristematic cells, the life-span of most cells in the meristem remains unchanged in treated roots. Thus, if cell proliferation and transition to elongation are regulated independently, any retardation of cell proliferation will automatically result in deceleration of the cell transition to elongation. Cell kinetics in roots is similar to that in some mammalian tissues capable of long-term proliferation.

Cell Division↗

PubMed1997

Induction of leaves directly from leaves in the maize mutant Lax midrib1-O.

One of the several phenes specified by the maize dominant mutation Lax midrib1-O (Lxm1-O on 3L) is the proliferation of leaf "flaps" usually paired around veins on the abaxial leaf surface. Using histology and scanning electron microscopy, we show these flaps to be authentic leaf structures; in rare instances, complete ectopic leaves are found. The first divisions preceding flap emergence occur between plastochrons 4 and 7, stages when the course of leaf differentiation is well under way. No sign of meristem or any small, densely cytoplasmic primordium-like cells were seen at the sites of flap initiation. In addition, the sites of ectopic leaf initiation do not express KNOX (Knotted-like homeobox) proteins, a molecular marker for shoot apical meristem cell identity. Thus, the cells that proliferate into ectopic leaves do not arise from a meristem or a primordium. A similar phenomenon has been described in several dicots, but in no other monocots. The details of flap morphology compared to the morphology of the leaf proper suggest a model whereby cells in regions of the leaf proper maintain the competence they acquired in the meristem. These cells then respond properly, in a regulated manner, to a delayed signal emanating from veins denoting "make the organ you are competent to make."

Meristem↗

PubMed2001

Developmental programmes in floral organ formation.

In contrast to animals, organogenesis in plants is continuous, allowing development in response to intrinsic and extrinsic signals. Organs arise from primordia formed on the flanks of meristems. The apical meristem produces primordia that acquire leaf identity, while floral meristems form primordia which develop into four organ types: sepals, petals, stamens and carpels. The production of mature organs involves two distinct processes, the initiation of organ primordia and the establishment of meristem, primordia and cell identities. Here we concentrate on floral organogenesis in Arabidopsis and examine the extent to which these processes utilize similar control mechanisms and regulatory molecules.

Arabidopsis↗

PubMed2000

Clonal analysis of the Arabidopsis root confirms that position, not lineage, determines cell fate.

The cellular organization of the Arabidopsis thaliana (L.) Heynh. root meristem suggests that a regular pattern of cell divisions occurs in the root tip. Deviations from this pattern of division might be expected to disrupt the organization of cells and tissues in the root. A clonal analysis of the 3-d-old primary root meristem was carried out to determine if there is variability in division patterns, and if so to discover their effect on cellular organization in the root. Clones induced in the seedling meristem largely confirmed the predicted pattern of cell divisions. However, the cellular initials that normally give rise to the different cell files in the root were shown to exhibit some instability. For example, it was calculated that a lateral root cap/epidermal initial is displaced every 13 d. Furthermore, the existence of large marked clones that included more than two adjacent cell layers suggests that intrusive growth followed by cell division may occur at low frequency, perhaps in response to local cell deaths in the meristem. These findings support the view that even in plant organs with stereotypical cell division patterns, positional information is still the key determinant of cell fate.

Arabidopsis↗

PubMed2003

Loss of CLE40, a protein functionally equivalent to the stem cell restricting signal CLV3, enhances root waving in Arabidopsis.

Continuous growth and development of plants is controlled by meristems that harbour stem cell pools. Division of stem cells and differentiation of their progeny are coordinated by intercellular signaling. In Arabidopsis, stem cells in shoot and floral meristems secrete CLAVATA3, a member of the CLE protein family that activates the CLV1/CLV2 receptor complex in underlying cells to restrict the size of the stem cell population. We found that CLE40 encodes a potentially secreted protein that is distantly related to CLV3. While CLV3 transcripts are confined to stem cells of the shoot system, CLE40 is expressed at low levels in all tissues, including roots. Misexpression and promoter swap experiments show that CLE40 can fully substitute for CLV3 to activate CLV signalling in the shoot, indicating that CLV3 and CLE40 are functionally equivalent proteins that differ mainly in their expression patterns. Analysis of cle40 mutants shows that wild-type expression levels of CLE40 are insufficient to contribute to CLV signalling. High level expression of CLV3 or CLE40 results in a premature loss of root meristem activity, indicating that activation of a CLV-like signaling pathway may restrict cell fate also in roots. The cellular organization of cle40 root meristems is normal, but mutant roots grow in a strongly waving pattern, suggesting a role for CLE40 in a signaling pathway that controls movement of the root tip.

Amino Acid Sequence↗

PubMed2006

Development of genotype-independent regeneration system for transformation of rice (Oryza sativa ssp. indica).

Rice (Oryza sativa ssp. indica) is an important economic crop in many countries. Although a variety of conventional methods have been developed to improve this plant, manipulation by genetic engineering is still complicated. We have established a system of multiple shoot regeneration from rice shoot apical meristem. By use of MS medium containing 4 mg L(-1) thidiazuron (TDZ) multiple shoots were successfully developed directly from the meristem without an intervening callus stage. All rice cultivars tested responded well on the medium and regenerated to plantlets that were readily transferred to soil within 5-8 weeks. The tissue culture system was suitable for Agrobacterium-mediated transformation and different factors affecting transformation efficiency were investigated. Agrobacterium strain EHA105 containing the plasmid pCAMBIA1301 was used. The lowest concentration of hygromycin B in combined with either 250 mg L(-1) carbenicillin or 250 mg L(-1) cefotaxime to kill the rice shoot apical meristem was 50 mg L(-1) and carbenicillin was more effective than cefotaxime. Two-hundred micromolar acetosyringone had no effect on the efficiency of transient expression. Sonication of rice shoot apical meristem for 10 s during bacterial immersion increased transient GUS expression in three-day co-cultivated seedlings. The gus gene was found to be integrated into the genome of the T(0) transformant plantlets.

Acetophenones↗

PubMed2006

Morphogenesis and patterning at the organ boundaries in the higher plant shoot apex.

Formation of lateral organ primordia from the shoot apical meristem creates boundaries that separate the primordium from surrounding tissue. Morphological and gene expression studies indicate the presence of a distinct set of cells that define the boundaries in the plant shoot apex. Cells at the boundary usually display reduced growth activity that results in separation of adjacent organs or tissues and this morphological boundary coincides with the border of different cell identities. Such morphogenetic and patterning events and their spatial coordination are controlled by a number of boundary-specific regulatory genes. The boundary may also act as a reference point for the generation of new meristems such as axillary meristems. Many of the genes involved in meristem initiation are expressed in the boundary. This review summarizes the cellular characters of the shoot organ boundary and the roles of regulatory genes that control different aspects of this unique region in plant development.

Arabidopsis↗

PubMed2005

KNOX action in Arabidopsis is mediated by coordinate regulation of cytokinin and gibberellin activities.

The shoot apical meristem (SAM) is a pluripotent group of cells that gives rise to the aerial parts of higher plants. Class-I KNOTTED1-like homeobox (KNOX) transcription factors promote meristem function partly through repression of biosynthesis of the growth regulator gibberellin (GA). However, regulation of GA activity cannot fully account for KNOX action. Here, we show that KNOX function is also mediated by cytokinin (CK), a growth regulator that promotes cell division and meristem function. We demonstrate that KNOX activity is sufficient to rapidly activate both CK biosynthetic gene expression and a SAM-localized CK-response regulator. We also show that CK signaling is necessary for SAM function in a weak hypomorphic allele of the KNOX gene SHOOTMERISTEMLESS (STM). Additionally, we provide evidence that a combination of constitutive GA signaling and reduced CK levels is detrimental to SAM function. Our results indicate that CK activity is both necessary and sufficient for stimulating GA catabolic gene expression, thus reinforcing the low-GA regime established by KNOX proteins in the SAM. We propose that KNOX proteins may act as general orchestrators of growth-regulator homeostasis at the shoot apex of Arabidopsis by simultaneously activating CK and repressing GA biosynthesis, thus promoting meristem activity.

Arabidopsis↗

PubMed2003

The pleiotropic mutation dar1 affects plant architecture in Arabidopsis thaliana.

Shoot architecture is shaped upon the organogenic activity of the shoot apical meristem (SAM). Such an activity relies on the balance between the maintenance of a population of undifferentiated cells in the centre of the SAM and the recruitment of organ founder cells at the periphery. A novel mutation in Arabidopsis thaliana, distorted architecture1 (dar1), is characterised by disturbed phyllotaxy of the inflorescence and consumption of the apical meristem late in development. SEM and light microscopy analyses of the dar1 SAM reveal an abnormal partitioning of meristematic domains, and mutations known to affect the SAM structure and function were found to interact with dar1. Moreover, the mutant shows an alteration of the root apical meristem (RAM) structure. Those observations support the hypothesis that DAR1 has a role in meristem maintenance and it is required for the normal development of Arabidopsis inflorescence during plant life.

Arabidopsis↗