Biomedical subjects

Wolfgang Werr

Publications and source records attributed to Wolfgang Werr.

11 recordsLinked to original sources

PubMed2006

The shoot stem cell niche in angiosperms: expression patterns of WUS orthologues in rice and maize imply major modifications in the course of mono- and dicot evolution.

In Arabidopsis, stem cell homeostasis in the shoot apical meristem (SAM) is controlled by a feedback loop between WUS and CLV functions. We have identified WUS orthologues in maize and rice by a detailed phylogenetic analysis of the WOX gene family and subsequent cloning. A single WUS orthologue is present in the rice genome (OsWUS), whereas the allotetraploid maize genome contains 2 WUS paralogues (ZmWUS1 and ZmWUS2). None of the isolated grass WUS orthologues displays an organizing center-type expression pattern in the vegetative SAM as in Arabidopsis. In contrast, the grass-specific expression patterns relate to the specification of new phytomers consistent with the transcriptional expression patterns of TD1 and FON1 (CLV1 orthologues of maize and rice, respectively). Moreover, the grass WUS and CLV1 orthologues are coexpressed in all reproductive meristems, where fasciation and supernumerary floral organs occur in td1 or fon1 loss-of-function mutants. The expression patterns of WUS orthologues in both grass species compared with those of dicots imply that major changes in WUS function, which are correlated with changes in CLV1 signaling, have occurred during angiosperm evolution and raise doubts about the uniqueness of the WUS/CLV antagonism in the maintenance of the shoot stem cell niche in grasses.

Amino Acid Sequence↗

PubMed2006

Transcription of the putative maize orthologue of the Arabidopsis DORNROSCHEN gene marks early asymmetry in the proembryo and during leaf initiation in the shoot apical meristem.

A potential orthologue of the Arabidopsis DORNROSCHEN (DRN) gene was isolated from maize based on phylogeny and expression patterns. ZmDRN transcription provides a new marker for embryonic patterning and cellular differentiation in the shoot apical meristem. In contrast to DRN expression in the 2-4-cell Arabidopsis embryo, transcription of the maize orthologue is activated only in the late proembryo stage where expression, however, marks the prospective scutellum domain such as DRN transcription prepatterns cotyledon development in the Arabidopsis globular embryo. The scutellum is commonly considered to be the grass specific organ, which is homologous to the pair of cotyledons in dicots. Such as in Arabidopsis, ZmDRN transcriptional activity is linked to the anlagen of new lateral organs in the maize apex. Striking with respect to the timing of cellular decisions during leaf initiation is asymmetry established between adjacent cells at the very tip of the shoot apical meristem.

Arabidopsis↗

PubMed2006

Nuclear import of the transcription factor SHOOT MERISTEMLESS depends on heterodimerization with BLH proteins expressed in discrete sub-domains of the shoot apical meristem of Arabidopsis thaliana.

The gene SHOOT MERISTEMLESS (STM) is required for the initiation and the maintenance of the shoot apical meristem (SAM) in Arabidopsis and encodes a MEINOX/three amino acid loop extension (TALE)-HD-type transcription factor. Translational fusions with the green fluorescent protein showed that STM is not nuclear by default. In a yeast two-hybrid screen performed with a meristem-enriched cDNA library, three interacting BLH (Bel1-like homeodomain) transcription factors were identified. According to bimolecular fluorescence complementation, STM is targeted into the nuclear compartment through heterodimerization with BLH partner proteins, which are expressed in distinct SAM domains from the center to the periphery. On a functional level, overexpression experiments in transgenic Arabidopsis plants suggest that individual heterodimers provide distinct contributions. These results contribute to our understanding of the STM transcription factor function in the SAM and also shed new light on the evolution of the TALE-HD super gene family in animal and plant lineages.

Active Transport, Cell Nucleus↗

PubMed2005

A transposon-based activation-tagging population in Arabidopsis thaliana (TAMARA) and its application in the identification of dominant developmental and metabolic mutations.

A population of 9471 stable activation-tagged lines was generated by transposable element mediated activation tagging mutagenesis in Arabidopsis (TAMARA) using the maize En/Spm transposon system. Based on DNA gel blot and flanking sequence analysis, this population contains approximately 6000 independent transposon insertions. A greenhouse-based screen identified six dominant or semi-dominant activation tagged mutants with obvious developmental alterations, among these a new pistillata mutant allele. In addition, a subset of 1500 lines was screened by a HPLC based high-throughput method for dominant activation tagged mutants with enhanced contents of phenolic compounds. One dominant activation tagged mutant (hpc1-1D) was isolated showing accumulation of a particular compound due to the upregulation of an R2R3-MYB transcription factor.

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↗

PubMed2005

Pattern formation in the monocot embryo as revealed by NAM and CUC3 orthologues from Zea mays L.

All aerial parts of a higher plant originate from the shoot apical meristem (SAM), which is initiated during embryogenesis as a part of the basic body plan. In contrast to dicot species, the SAM in Zea mays is not established at an apico-central, but at a lateral position of the transition stage embryo. Genetic and molecular studies in dicots have revealed that members of the NAC gene family of plant-specific transcription factors such as NO APICAL MERISTEM (NAM) from Petunia or the CUP-SHAPED COTYLEDON (CUC) genes from Arabidopsis contribute essential functions to the establishment of the SAM and cotyledon separation. As an approach to the understanding of meristem formation in a monocot species, members of the maize NAC family highly related to the NAM/CUC genes were isolated and characterized. Our phylogenetic analysis indicates that two distinct NAM and CUC3 precursors already existed prior to the separation of mono- and dicot species. The allocation of the two maize paralogues, ZmNAM1 and ZmNAM2 together with PhNAM, AtCUC2 and AmCUP in one sub-branch and the corresponding expression patterns support their contribution to SAM establishment. In contrast, the ZmCUC3 orthologue is associated with boundary specification at the SAM periphery, where it visualizes which fraction of cells in the SAM is committed to a new leaf primordium. Other maize NAC gene family members are clearly positioned outside of this NAM/CUC3 branch and also exhibit highly cell type-specific expression patterns.

Amino Acid Sequence↗

PubMed2004

The maize duplicate genes narrow sheath1 and narrow sheath2 encode a conserved homeobox gene function in a lateral domain of shoot apical meristems.

The narrow sheath (ns) phenotype of maize is a duplicate factor trait conferred by mutations at the unlinked loci ns1 and ns2. Recessive mutations at each locus together confer the phenotypic deletion of a lateral compartment in maize leaves and leaf homologs. Previous analyses revealed that the mediolateral axis of maize leaves is comprised of at least two distinct compartments, and suggest a model whereby NS function is required to recruit leaf founder cells from a lateral compartment of maize meristems. Genomic clones of two maize homeodomain-encoding genes were isolated by homology to the WUSCHEL-related gene PRESSED FLOWER (PRS). PRS is required for lateral sepal development in Arabidopsis, although no leaf phenotype is reported. Co-segregation of the ns phenotype with multiple mutant alleles of two maize PRS homologs confirms their allelism to ns1 and ns2. Analyses of NS protein accumulation verify that the ns-R mutations are null alleles. ns transcripts are detected in two lateral foci within maize meristems, and in the margins of lateral organ primordia. Whereas ns1 and ns2 transcripts accumulate to equivalent levels in shoot meristems of vegetative seedlings, ns2 transcripts predominate in female inflorescences. Previously undiscovered phenotypes in the pressed flower mutant support a model whereby the morphology of eudicot leaves and monocot grass leaves has evolved via the differential elaboration of upper versus lower leaf zones. A model implicating an evolutionarily conserved NS/PRS function during recruitment of organ founder cells from a lateral domain of plant meristems is discussed.

Amino Acid Sequence↗

PubMed2003

When negative is positive in functional genomics.

The post-genomic era has caused classical approaches to analyse gene function to be reviewed and refined. Conventional reverse genetic approaches to predict gene function have drawbacks in terms of genetic redundancy and being limited mainly to well-characterized genomes. The relatively recent use of dominant-negative transgenes has been successful in elaborating certain pathways and it is now possible to extend this technique to convert transcription factors into dominant repressor functions by fusion to repressor domains such as ENGRAILED from Drosophila. This methodology opens up new possibilities to overcome genetic redundancy, to identify novel gene functions and also to apply information on conserved protein domains between species to repress heterologous protein function.

Animals↗

PubMed2003

Generation of dominant-negative effects on the heat shock response in Arabidopsis thaliana by transgenic expression of a chimaeric HSF1 protein fusion construct.

Upon heat stress, heat shock factors (HSFs) control the expression of heat shock protein (HSP) genes by transcriptional activation. The perplexing multiplicity of HSF genes in Arabidopsis- 21 potential genes have been identified - renders it difficult to identify mutant phenotypes. In this study, we have attempted to generate a transdominant-negative mutant of HSF by transgenic expression of a protein fusion construct, EN-HSF1, consisting of the Drosophila engrailed repressor domain (EN) and the complete Arabidopsis AtHSF1. Transgenic lines were screened for impaired ability to induce high levels of low-molecular-weight heat shock proteins (sHSPs). Two lines, EH14-6 and EH16-3, which showed quantitative differences in the expression of EN-HSF1, were further analysed for induction of thermotolerance and heat-stress-dependent mRNAs of a number of different HSF target genes encoding different HSP and HSF. The mRNA levels of all genes tested were moderately downregulated in EH14-6 but strongly reduced in EH16-3 plants compared to wild-type (Wt) and HSF1-overexpressing control plants. The inhibition of the induction of heat shock response correlated with impaired basal and acquired thermotolerance of the EH16-3 line. The kinetics of HSP expression suggest that the negative effect of EN-HSF1 is stronger in the early phase of the heat shock response, and that the reduction in mRNA levels is partially compensated at the translational level.

Arabidopsis↗

PubMed2003

The DORNROSCHEN/ENHANCER OF SHOOT REGENERATION1 gene of Arabidopsis acts in the control of meristem ccll fate and lateral organ development.

The two main tasks of a meristem, self-perpetuation and organ initiation, are separated spatially. Slowly dividing cells in the meristem center act as pluripotent stem cells, and only their derivatives in the meristem periphery specify new organs. Meristem integrity and cellular proliferation are controlled in part by regulatory interactions between genes that are expressed in specific subdomains of the meristem. Using transposon-mediated activation tagging, we have identified Dornröschen (drn-D) mutants of Arabidopsis that prematurely arrest shoot meristem activity with the formation of radialized lateral organs. The mutated gene (DRN/ESR1), which encodes an AP2/ERF protein, is expressed in a subdomain of meristem stem cells, in lateral organ anlagen, and transiently in the distal domain of organ primordia. During the development of drn-D mutants, expression of the homeobox gene SHOOTMERISTEMLESS is downregulated and later reactivated in an altered domain. In addition, we found increased expression of CLAVATA3 and WUSCHEL, two genes that antagonistically regulate stem cell fate in meristems. These findings suggest that the DRN/ESR1 gene product is involved in the regulation of gene expression patterns in meristems. Furthermore, specific misexpression of DRN in meristem stem cells affects organ polarity and outgrowth in the meristem periphery, indicating that DRN/ESR1 itself, or a process regulated by DRN/ESR1, can act non-cell-autonomously. We elaborate on the role of DRN/ESR1 in meristem and organ development and discuss its possible role in the process of shoot regeneration.

Alleles↗

PubMed2002

Translational fusions with the engrailed repressor domain efficiently convert plant transcription factors into dominant-negative functions.

Evidence is provided that plant transcription factors can be efficiently reprogrammed to dominant- negative functions by the use of a repressor domain of the engrailed (en) gene from Drosophila. Ectopic expression of translational fusions between the en(298) N-terminus and the complete coding regions of the SHOOTMERISTEMLESS, APETALA3, PISTILLATA and KNAT1 transcription factors results in trans-dominant functions which phenocopy loss-of-function mutants. The combination of the dominant-negative en(298)-STM function with the hormone-binding domain of the glucocorticoid receptor provides strong evidence that phenocopies rely on the incorporation of the chimeric protein into the nuclear compartment. By this dominant-negative approach KNAT1 was rapidly identified to be encoded by the BREVIPEDICELLUS locus. Dominant-negative chimeric proteins may be of wide use to elucidate biological functions of plant transcriptional activators and may be suitable to study protein-protein interactions in planta.

Alleles↗