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T Berleth

Publications and source records attributed to T Berleth.

16 recordsLinked to original sources
PubMed2001

Plant morphogenesis: long-distance coordination and local patterning.

The overall morphology of a plant is largely determined by developmental decisions taken within or near the terminally positioned apical meristems of shoots and roots. The spatial separation of these developmental centers emphasizes the need for long-distance signaling. The same signaling events may simultaneously coordinate differentiation within meristems and in the connecting vascular tissues. Recent genetic and molecular analyses not only confirm the proposed role of auxin as a coordinating signal across the plant, but also implicate auxin as a patterning signal in embryo and meristem organization.

Morphogenesis↗
PubMed2000

Plant development: hidden networks.

How the complex patterns of plant vascular systems are generated is largely unknown. Advances in understanding vascular pattern formation at various levels are likely to follow recent large-scale genetic screens for Arabodopsis mutants with abnormal vascular systems.

Arabidopsis↗
PubMed2000

Vascular continuity and auxin signals.

Plant vascular tissues form systems of interconnected cell files throughout the plant body. Vascular tissues usually differentiate at predictable positions but the wide range of functional patterns generated in response to abnormal growth conditions or wounding reveals partially self-organizing patterning mechanisms. Signals ensuring aligned cell differentiation within vascular strands are crucial in self-organized vascular patterning, and the apical-basal flow of indole acetic acid has been suspected to act as an orienting signal in this process. Several recent advances appear to converge on a more precise definition of the role of auxin flow in vascular tissue patterning.

Arabidopsis↗
PubMed2000

Vascular development: tracing signals along veins.

The plant hormone auxin has been implicated in vascular development, but the molecular details of patterned vascular differentiation have remained elusive. Research in the past year has identified new genes that control vascular patterning, and auxin transport and perception. New experimental strategies have been employed to study vascular development. Together, these findings have generated a conceptual framework and experimental tools for the exploration of vascular-tissue patterning at the molecular level.

Arabidopsis↗
PubMed1999

A molecular basis for auxin action.

The plant hormone auxin is central in the regulation of growth and development, however, the molecular basis for its action has remained enigmatic. In the absence of a molecular model, the wide range of responses elicited by auxin have been difficult to explain. Recent advances using molecular genetic approaches in Arabidopsis have led to the isolation of a number of key genes involved in auxin action. Of particular importance are genes involved in channelling polar auxin transport through the plant. In addition a model for auxin signal transduction, centred on regulated protein degradation, has been developed.

Arabidopsis↗
PubMed1999

Responses of plant vascular systems to auxin transport inhibition.

To assess the role of auxin flows in plant vascular patterning, the development of vascular systems under conditions of inhibited auxin transport was analyzed. In Arabidopsis, nearly identical responses evoked by three auxin transport inhibitor substances revealed an enormous plasticity of the vascular pattern and suggest an involvement of auxin flows in determining the sites of vascular differentiation and in promoting vascular tissue continuity. Organs formed under conditions of reduced auxin transport contained increased numbers of vascular strands and cells within those strands were improperly aligned. In leaves, vascular tissues became progressively confined towards the leaf margin as the concentration of auxin transport inhibitor was increased, suggesting that the leaf vascular system depends on inductive signals from the margin of the leaf. Staged application of auxin transport inhibitor demonstrated that primary, secondary and tertiary veins became unresponsive to further modulations of auxin transport at successive stages of early leaf development. Correlation of these stages to anatomical features in early leaf primordia indicated that the pattern of primary and secondary strands becomes fixed at the onset of lamina expansion. Similar alterations in the leaf vascular responses of alyssum, snapdragon and tobacco plants suggest common functions of auxin flows in vascular patterning in dicots, while two types of vascular pattern alterations in Arabidopsis auxin transport mutants suggest that at least two distinct primary defects can result in impaired auxin flow. We discuss these observations with regard to the relative contributions of auxin transport, auxin sensitivity and the cellular organisation of the developing organ on the vascular pattern.

Arabidopsis↗
PubMed1998

The Arabidopsis gene MONOPTEROS encodes a transcription factor mediating embryo axis formation and vascular development.

The vascular tissues of flowering plants form networks of interconnected cells throughout the plant body. The molecular mechanisms directing the routes of vascular strands and ensuring tissue continuity within the vascular system are not known, but are likely to depend on general cues directing plant cell orientation along the apical-basal axis. Mutations in the Arabidopsis gene MONOPTEROS (MP) interfere with the formation of vascular strands at all stages and also with the initiation of the body axis in the early embryo. Here we report the isolation of the MP gene by positional cloning. The predicted protein product contains functional nuclear localization sequences and a DNA binding domain highly similar to a domain shown to bind to control elements of auxin inducible promoters. During embryogenesis, as well as organ development, MP is initially expressed in broad domains that become gradually confined towards the vascular tissues. These observations suggest that the MP gene has an early function in the establishment of vascular and body patterns in embryonic and post-embryonic development.

Amino Acid Sequence↗
PubMed1998

Root development: new meanings for root canals?

During Arabidopsis root development, a radial pattern of tissues is extended by the meristem. These tissues form continuous layers and recent data suggest that tissue continuity is instrumental for constraining the direction of signaling in a process termed channeling. In the ground tissue, fate-determining signals originate from contiguous cells of the same layer, possibly due to specific symplastic connections. Mutant analysis supports the hypothesis that vascular tissue continuity may facilitate and depend on the directional transport of a vascular fate-determining signal, possibly the phytohormone auxin.

Arabidopsis↗
PubMed1996

Genetic similarity among Arabidopsis thaliana ecotypes estimated by DNA sequence comparison.

DNA polymorphisms among Arabidopsis thaliana ecotypes are widely used as genetic markers in map-based cloning strategies. New PCR-based molecular markers do not only facilitate molecular mapping, but can also be used to obtain reliable sequence information for cladistic analyses. We have used CAPS (cleaved amplified polymorphic sequences) markers and a direct sequencing strategy to estimate genetic similarity among eighteen Arabidopsis ecotypes. Sequences at four loci, two from the nuclear and two from a non-nuclear genome, were analysed. For each ecotype more than 1000 bp of sequence information was obtained, and genetic similarity was calculated from a total of 35 polymorphic sites using a character-based approach. Divergence ranged from zero up to 50 discordant characters among the 72 characters defined by the polymorphisms. Separate calculations based on the nuclear and the non-nuclear sequences were performed and revealed a number of common features, including the existence of small clusters of very closely related ecotypes separated from each other by extensive sequence divergence. Our results provide information useful especially to investigators setting up crosses for chromosome landing strategies.

Arabidopsis↗
PubMed1996

Studies on the role of the Arabidopsis gene MONOPTEROS in vascular development and plant cell axialization.

In the embryo of Arabidopsis thaliana (L.) Heynh., formation of the hypocotyl/root axis is initiated at the early-globular stage, recognizable as oriented expansion of formerly isodiametric cells. The process depends on the activity of the gene MONOPTEROS (MP); mp mutant embryos fail to produce hypocotyl and radicle. We have analyzed the morphology and anatomy of mp mutant plants throughout the Arabidopsis life cycle. Mutants form largely normal rosettes and root systems, but inflorescences either fail to form lateral flowers or these flowers are greatly reduced. Furthermore, the auxin transport capacity of inflorescence axes is impaired and the vascular strands in all analyzed organs are distorted. These features of the mutant phenotype suggest that the MP gene promotes cell axialization and cell file formation at multiple stages of plant development.

Arabidopsis↗
PubMed1996

Genetic and contig map of a 2200-kb region encompassing 5.5 cM on chromosome 1 of Arabidopsis thaliana.

In the course of the isolation of the MONOPTEROS (MP) gene, required for primary root formation in Arabidopsis thaliana, a yeast artificial chromosome (YAC) contig encompassing approximately 2200 kilobases corresponding to 5.5 cM on the top arm of chromosome 1 was established. Forty-six YAC clones were characterized and 12 new restriction fragment length polymorphism (RFLP) markers are presented. Three new codominant amplified polymorphic sequence (CAPS) markers were generated that enabled high resolution genetic mapping and correlation of physical and genetic distances along the contig. The map contributes to the completion of a physical map of the Arabidopsis genome and should facilitate positional cloning of other genes in the region as well as studies on genome organization. We also present another set of 11 physically linked probes, as well as mapping data for additional RFLP markers within a broader interval of 10.4 cM.

Arabidopsis↗
PubMed1989

Multiple steps in the localization of bicoid RNA to the anterior pole of the Drosophila oocyte.

The anterior region of the Drosophila embryonic pattern is determined by a gradient of the bicoid (bcd) protein. The correct formation of this gradient requires the localization of bcd RNA to the anterior pole of the egg. Here we use a wholemount in situ technique to examine the process of bcd RNA localization during oogenesis and embryogenesis. While bcd protein becomes distributed in a gradient that extends throughout the anterior two thirds of the early embryo, bcd RNA remains restricted to a much smaller region at the anterior pole. The difference between these distributions indicates that the shape of the protein gradient must depend to some extent on the posterior movement of the protein after it has been synthesized. Four distinct phases of bcd RNA localization can be distinguished during oogenesis. Between stages 6 and 9 of oogenesis, the RNA accumulates in a ring at the anterior end of the oocyte. During the second phase, in stage 9-10a follicles, the RNA also localizes to the apical regions of the nurse cells, demonstrating that the nurse cells possess an intrinsic polarity. As the nurse cells contract during stages 10b-11, all of the bcd RNA becomes localized to the cortex at the anterior end of the oocyte. During a final phase that must occur between stage 12 of oogenesis and egg deposition, the RNA becomes localized to a spherical region that occupies a slightly dorsal position at the anterior pole.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

The role of localization of bicoid RNA in organizing the anterior pattern of the Drosophila embryo.

The organization of the anterior pattern in the Drosophila embryo is mediated by the maternal effect gene bicoid. bcd has been identified in an 8.7-kb genomic fragment by germ line transformants that completely rescue the mutant phenotype. The major transcript of 2.6 kb includes a homeobox with low homology to previously known homeoboxes, a PRD-repeat and a M-repeat. In situ hybridizations reveal that bcd is transcribed in the nurse cells. The mRNA is localized at the anterior tip of oocyte and early embryo until the cellular blastoderm stage. The localization of the transcript requires the function of the maternal effect genes exuperantia and swallow while transcript stability is reduced by functions depending on posterior group genes.

Alleles↗
PubMed1987

Activation of endogenous retroviral genomes in Mov strains of mice.

A collection of Mov mouse strains, each carrying in their germ line a Moloney murine leukaemia virus (M-MuLV) proviral genome at a different chromosomal location, was used to study expression of endogenous retroviruses. No M-MuLV-specific RNA was detected in the non-viraemic Mov strains studied, indicating that less than two copies of RNA are transcribed per cell. Virus expression was seen in three viraemic Mov strains. In Mov-3 mice the provirus was activated shortly after birth, whereas proviruses in Mov-9 and Mov-14 were activated at different stages of embryogenesis. The results suggest that the chromosomal position influences proviral expression during development. The first appearance of virus particles was not accompanied by detectable amounts of viral transcripts, suggesting that viraemia is a consequence of provirus activation in a small, as yet unidentified, population of cells, followed by virus spread and infection of susceptible cells.

Age Factors↗