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Biomedical subjects

V Raz

Publications and source records attributed to V Raz.

8 recordsLinked to original sources
PubMed2001

A QTL for flowering time in Arabidopsis reveals a novel allele of CRY2.

Variation of flowering time is found in the natural populations of many plant species. The underlying genetic variation, mostly of a quantitative nature, is presumed to reflect adaptations to different environments contributing to reproductive success. Analysis of natural variation for flowering time in Arabidopsis thaliana has identified several quantitative trait loci (QTL), which have yet to be characterized at the molecular level. A major environmental factor that determines flowering time is photoperiod or day length, the length of the light period, which changes across the year differently with geographical latitude. We identified the EDI locus as a QTL partly accounting for the difference in flowering response to the photoperiod between two Arabidopsis accessions: the laboratory strain Landsberg erecta (Ler), originating in Northern Europe, and Cvi, collected in the tropical Cape Verde Islands. Positional cloning of the EDI QTL showed it to be a novel allele of CRY2, encoding the blue-light photoreceptor cryptochrome-2 that has previously been shown to promote flowering in long-day (LD) photoperiods. We show that the unique EDI flowering phenotype results from a single amino-acid substitution that reduces the light-induced downregulation of CRY2 in plants grown under short photoperiods, leading to early flowering.

Alleles↗
PubMed2001

Cell division activity during apical hook development.

Growth during plant development is predominantly governed by the combined activities of cell division and cell elongation. The relative contribution of both activities controls the growth of a tissue. A fast change in growth is exhibited at the apical hypocotyl of etiolated seedlings where cells grow at different rates to form a hook-like structure, which is traditionally assumed to result from differential cell elongation. Using new tools we show asymmetric distribution of cell division during early stages of hook development. Cell divisions in the apical hook were predominantly found in subepidermal layers during an early step of hook development, but were absent in mutants exhibiting a hookless phenotype. In addition, during exaggeration of hook curvature, which is mediated by ethylene, a rapid change in the combined activities of cell division and cell elongation was detected. Our results indicate a fast change in cell division activity during apical hook development. We suggest that cell division together with cell elongation contributes to apical hook growth. Our results emphasize the change in the relative contribution of cell division and cell elongation in a fast growing structure like the apical hook.

Aphidicolin↗
PubMed2001

Sequential steps for developmental arrest in Arabidopsis seeds.

The continuous growth of the plant embryo is interrupted during the seed maturation processes which results in a dormant seed. The embryo continues development after germination when it grows into a seedling. The embryo growth phase starts after morphogenesis and ends when the embryo fills the seed sac. Very little is known about the processes regulating this phase. We describe mutants that affect embryo growth in two sequential developmental stages. Firstly, embryo growth arrest is regulated by the FUS3/LEC type genes, as mutations in these genes cause a continuation of growth in immature embryos. Secondly, a later stage of embryo dormancy is regulated by ABI3 and abscisic acid; abi3 and aba1 mutants exhibit premature germination only after embryos mature. Mutations affecting both developmental stages result in an additive phenotype and double mutants are highly viviparous. Embryo growth arrest is regulated by cell division activities in both the embryo and the endosperm, which are gradually switched off at the mature embryo stage. In the fus3/lec mutants, however, cell division in both the embryo and endosperm is not arrested, but rather is prolonged throughout seed maturation. Furthermore ectopic cell division occurs in seedlings. Our results indicate that seed dormancy is secured via at least two sequential developmental processes: embryo growth arrest, which is regulated by cell division and embryo dormancy.

Arabidopsis↗
PubMed1999

Regulation of differential growth in the apical hook of Arabidopsis.

Arabidopsis seedlings develop a hook-like structure at the apical part of the hypocotyl when grown in darkness. Differential cell growth processes result in the curved hypocotyl hook. Time-dependent analyses of the hypocotyl showed that the apical hook is formed during an early phase of seedling growth and is maintained in a sequential phase by a distinct process. Based on developmental genetic analyses of hook-affected mutants, we show that the hookless mutants (hls1, cop2) are involved in an early aspect of hook development. From time-dependent analyses of ethylene-insensitive mutants, later steps in hook maintenance were found to be ethylene sensitive. Regulation of differential growth was further studied through examination of the spatial pattern of expression of two hormone-regulated genes: an ethylene biosynthetic enzyme and the ethylene receptor ETR1. Accumulation of mRNA for AtACO2, a novel ACC (1-aminocyclopropane-1-carboxylic acid) oxidase gene, occurred within cells predominantly located on the outer-side of the hook and was tightly correlated with ethylene-induced exaggeration in the curvature of the hook. ETR1 expression in the apical hook, however, was reduced by ethylene treatment. Based on the expression pattern of ETR1 and AtACO2 in the hook-affected mutants, a model for hook development and maintenance is proposed.

Amino Acid Oxidoreductases↗
PubMed1996

PK12, a plant dual-specificity protein kinase of the LAMMER family, is regulated by the hormone ethylene.

The ethylene signal is transduced in plant cells via phosphorylation events. To identify protein kinases whose levels of expression are modulated by the plant hormone ethylene, we utilized a differential reverse transcriptase-polymerase chain reaction approach using mRNA extracted from ethylene-treated and untreated tobacco leaves. An ethylene-induced cDNA clone, PK12, encoding a protein kinase, was isolated. PK12 is a new member of the recently defined LAMMER family of protein kinases, which has been identified in mammals, flies, yeasts, and plants. The LAMMER kinases are related to the cell cycle-dependent CDC2-type kinases and are characterized by their similarity at kinase subdomain X. The recombinant PK12 protein autophosphorylates in vitro on serine, threonine, and tyrosine residues, thereby making it a member of the dual-specificity protein kinases. Immunoprecipitation of PK12 from plant extracts and kinase assay revealed that the apparent PK12 activity is rapidly and transiently increased when plants are treated with ethylene. By using in situ hybridization, we detected accumulation of the PK12 transcript in leaves after ethylene treatment and in the untreated flower abscission zone. The tissue in this zone is known to constitutively express ethylene-regulated genes.

Amino Acid Sequence↗
PubMed1995

Dark induction and subcellular localization of the pathogenesis-related PRB-1b protein.

The PRB-1b gene codes for a basic-type pathogenesis-related protein of the PR-1 family of tobacco. PRB-1b mRNA accumulation is induced in response to biotic and abiotic elicitors, such as TMV, ethylene, salicylic acid, alpha-amino butyric acid and darkness. In order to determine the location of elements that control dark-regulated PRB-1b gene expression, we tested promoter, transcribed regions and 3'-downstream regions of the gene for their ability to respond to dark induction in transgenic tobacco plants. An ethylene-inducible promoter region of 863 bp was not able to confer dark induction to a beta-glucuronidase reporter gene, while a construct containing the transcribed region of the gene and 3'-downstream sequences, driven by the cauliflower mosaic virus 35S promoter, was correctly dark-regulated. The results indicate that dark-induction of the PRB-1b gene can be controlled by 3'-downstream elements at the transcriptional level or by transcribed sequences at the post-transcriptional level. A circadian clock regulation of the PRB-1b gene was excluded, as fluctuations of PRB-1b transcript levels were not observed in plants placed in constant light or darkness. Subcellular localization of the PRB-1b protein was also determined, in tobacco protoplasts preparations and in cell cultures. The PRB-1b polypeptide was predominantly detected in protoplast vacuoles and was not secreted to the media in cell cultures. These results support an intracellular localization for the PRB-1b protein, as reported for other basic-type components of the pathogenesis-related proteins family.

Cells, Cultured↗
PubMed1991

PCR-based identification of new receptors: molecular cloning of a receptor for fibroblast growth factors.

Transmembrane tyrosine kinases are involved in the control of cell growth and differentiation by extracellular signals. To enable identification of new receptor tyrosine kinases we developed a method that selectively amplifies segments of receptor genes. The method is based on a combination of polymerase chain reaction (PCR) and hybridization screening and it employs three oligonucleotide primers derived from conserved domains of receptor tyrosine kinases. It yields amplification of receptors' genes and appears to ignore cytoplasmic tyrosine kinases. When applied to RNA from 12.5 days post coitum mouse placenta, this methodology resulted in the detection of several putative or established receptors. Molecular cloning of one of these genes, which is identical to the partially characterized bek gene, identified a transmembrane tyrosine kinase with three immunoglobulin-like domains in the extracellular portion, and a cytoplasmic tyrosine kinase sequence. The isolated cDNA shows remarkable homology to the murine flg gene that encodes a receptor for fibroblast growth factors. Indeed, an antibody directed to the carboxy terminus of the deduced bek protein specifically recognized a receptor for acidic and basic fibroblast growth factors in murine hepatoma cells. We therefore expect that the methodology we developed will enable the study of new receptors in hardly accessible biological systems such as early mammalian embryos or stem cells.

Amino Acid Sequence↗