Biomedical subjects

Mieke Van Lijsebettens

Publications and source records attributed to Mieke Van Lijsebettens.

6 recordsLinked to original sources

PubMed2006

Leader sequence of a plant ribosomal protein gene with complementarity to the 18S rRNA triggers in vitro cap-independent translation.

Cap-independent translation (CIT) occurs at the leader sequences of uncapped plant viral RNAs, but also at a number of normally capped cellular mRNAs and has been correlated with sequence complementarity to 18S rRNA. The ribosomal protein S18 (RPS18) is a component of the small ribosomal subunit and is encoded by three gene copies (A, B, and C) in the Arabidopsis thaliana genome. The RPS18C mRNA was most abundant and contained a short 5' untranslated region of 84 bp that is complementary to a novel putative interaction site at the 3' end of the 18S rRNA. The RPS18C leader mediated CIT as demonstrated by dicistronic constructs consisting of luciferase and chloramphenicol acetyl transferase reporter genes in an in vitro wheat germ extract system. CIT was rapidly inhibited upon addition of an oligonucleotide that competed for the 18S rRNA site complementary to the RPS18C leader and interfered with polysome assembly at the transcript.

3' Untranslated Regions↗

PubMed2006

The TORNADO1 and TORNADO2 genes function in several patterning processes during early leaf development in Arabidopsis thaliana.

In multicellular organisms, patterning is a process that generates axes in the primary body plan, creates domains upon organ formation, and finally leads to differentiation into tissues and cell types. We identified the Arabidopsis thaliana TORNADO1 (TRN1) and TRN2 genes and their role in leaf patterning processes such as lamina venation, symmetry, and lateral growth. In trn mutants, the leaf venation network had a severely reduced complexity: incomplete loops, no tertiary or quaternary veins, and vascular islands. The leaf laminas were asymmetric and narrow because of a severely reduced cell number. We postulate that the imbalance between cell proliferation and cell differentiation and the altered auxin distribution in both trn mutants cause asymmetric leaf growth and aberrant venation patterning. TRN1 and TRN2 were epistatic to ASYMMETRIC LEAVES1 with respect to leaf asymmetry, consistent with their expression in the shoot apical meristem and leaf primordia. TRN1 codes for a large plant-specific protein with conserved domains also found in a variety of signaling proteins, whereas TRN2 encodes a transmembrane protein of the tetraspanin family whose phylogenetic tree is presented. Double mutant analysis showed that TRN1 and TRN2 act in the same pathway.

Arabidopsis↗

PubMed2005

The elongata mutants identify a functional Elongator complex in plants with a role in cell proliferation during organ growth.

The key enzyme for transcription of protein-encoding genes in eukaryotes is RNA polymerase II (RNAPII). The recruitment of this enzyme during transcription initiation and its passage along the template during transcription elongation is regulated through the association and dissociation of several complexes. Elongator is a histone acetyl transferase complex, consisting of six subunits (ELP1-ELP6), that copurifies with the elongating RNAPII in yeast and humans. We demonstrate that point mutations in three Arabidopsis thaliana genes, encoding homologs of the yeast Elongator subunits ELP1, ELP3 (histone acetyl transferase), and ELP4 are responsible for the phenotypes of the elongata2 (elo2), elo3, and elo1 mutants, respectively. The elo mutants are characterized by narrow leaves and reduced root growth that results from a decreased cell division rate. Morphological and molecular phenotypes show that the ELONGATA (ELO) genes function in the same biological process and the epistatic interactions between the ELO genes can be explained by the model of complex formation in yeast. Furthermore, the plant Elongator complex is genetically positioned in the process of RNAPII-mediated transcription downstream of Mediator. Our data indicate that the Elongator complex is evolutionarily conserved in structure and function but reveal that the mechanism by which it stimulates cell proliferation is different in yeast and plants.

Acetyltransferases↗

PubMed2005

Historical perspectives on plant developmental biology.

The early studies of plant growth and development focused on embryogenesis. In the past twenty five years, it became possible to successfully analyze many more developmental processes, hence plant developmental biology became the generally accepted terminology. It refers to a multidisciplinary approach using expertise and tools from genetics, molecular biology and cell biology to study processes in development also beyond the formation of the embryo. Around that time, initiatives were taken to address biological questions in just a few model systems, such as Arabidopsis thaliana, Zea mays, Antirrhinum majus and Petunia hybrida, while the < > model systems, i.e. potato, tobacco, used in regeneration and grafting experiments, were increasingly abandoned. International research programs were initiated in Arabidopsis at first to create stock centers and databases to proceed faster with the scientific research and to get deeper insight into plant biology. During the last five years the maize community made tremendous progress in developing tools and resources for their system. Milestones in plant developmental biology discussed relate to the molecular-genetic approach to study embryogenesis, autoregulation of meristems, leaf and flower initiation, leaf and flower formation and cell specification in the root. Developmental biology changed the research from descriptive to causal resulting in a number of genetic models. Future developments in research will focus on the study of a specific gene activity in a genome-wide context. The building of molecular networks will allow computer modeling of biological processes and its use for predictions and further experimentation. Sequence information derived from the multiple genome projects will be exploited in comparative biology.

DNA, Plant↗

PubMed2004

The rotunda2 mutants identify a role for the LEUNIG gene in vegetative leaf morphogenesis.

Leaf development in Arabidopsis thaliana is considered to be a two-step process. In the first step, a leaf primordium is formed that involves a switch from indeterminate to leaf developmental fate in the shoot apical meristem cells. The second step, known as leaf morphogenesis, consists of post-initiation developmental events such as patterned cell proliferation, cell expansion, and cell differentiation. The results are presented of the molecular and genetic analyses of the rotunda2 (ron2) mutants of Arabidopsis, which were isolated based on their wide and serrated vegetative leaf lamina. The RON2 gene was positionally cloned and was identical to LEUNIG (LUG); it encodes a transcriptional co-repressor that has been described to affect flower development. Morphological and histological analyses of expanded leaves indicated that RON2 (LUG) acts at later stages of leaf development by restricting cell expansion during leaf growth. Real-time reverse-transcription polymerase chain reaction was used to quantify the expression of KNOX, WUSCHEL, YABBY3, LEAFY, ASYMMETRIC LEAVES, and GIBBERELLIN OXIDASE genes in expanding and fully expanded rosette leaf laminas of the wild type and ron2 and lug mutants. SHOOTMERISTEMLESS was expressed in wild-type leaves and down-regulated in the mutants. The results indicate that RON2 (LUG) has a function in later stages of leaf development.

Amino Acid Sequence↗

PubMed2003

DRL1, a homolog of the yeast TOT4/KTI12 protein, has a function in meristem activity and organ growth in plants.

The DEFORMED ROOTS AND LEAVES1 (DRL1) gene is single copy in the Arabidopsis genome, and based on overall amino acid similarity and conservation of functional domains, the DRL1 protein is homologous with yeast TOT4/KTI12. TOT4/KTI12 associates with Elongator, a multisubunit complex that binds the RNA polymerase II transcription elongation complex. Recessive mutations at the DRL1 locus caused defective organ formation indicative of disorganized shoot, inflorescence, flower, and root meristems. DRL1 is a putative ATP/GTP binding protein; in addition, calmodulin binding activity was demonstrated in vitro for the C terminus of the DRL1 protein. Phenotypic and genetic data position DRL1 relative to regulatory loci for leaf development, in which it acts early. We identified Arabidopsis homologs for the six Elongator components and hypothesize that DRL1 regulates transcription elongation through a putative plant Elongator. Upregulation of the ANGUSTIFOLIA transcript in the strong drl1-2 allele supports this model.

Adaptor Proteins, Signal Transducing↗