[CYTOPLASMIC LOCALIZATION OF NEUN/Fox-3 NUCLEAR PROTEIN IN THE PANCREATIC CELLS]

The study of the sections of Wistar rat pancreas (n=4) using the methods of immunocytochemistry and confocal laser microscopy has demonstrated previously unknown fact of the presence of NeuN protein in the secretory epithelial cells of the exocrine part of this organ. The protein was located in the apical part of the cytoplasm slightly below the zone of zymogen granules. Until now the nuclear protein NeuN was considered to be the panneuronal differentiation marker and was used in the studies of neurogenesis.

TRIPTYCHON and CAPRICE mediate lateral inhibition during trichome and root hair patterning in Arabidopsis

Trichome patterning in Arabidopsis is a model for the generation of a spacing pattern from initially equivalent cells. We show that the TRIPTYCHON gene that functions in lateral inhibition encodes a single-repeat MYB-related transcription factor that lacks a recognizable activation domain. It has high sequence similarity to the root hair patterning gene CAPRICE. Both genes are expressed in trichomes and act together during lateral inhibition. We further show that TRIPTYCHON and CAPRICE act redundantly in the position-dependent cell fate determination in the root epidermis. Thus, the same lateral inhibition mechanism seems to be involved in both de novo patterning and position-dependent cell determination. We propose a model explaining trichome and root hair patterning by a common mechanism.

The cell morphogenesis gene ANGUSTIFOLIA encodes a CtBP/BARS-like protein and is involved in the control of the microtubule cytoskeleton

The ANGUSTIFOLIA (AN) gene is required for leaf hair (trichome) branching and is also involved in polarized expansion underlying organ shape. Here we show that the AN gene encodes a C-terminal binding proteins/brefeldin A ADP-ribosylated substrates (CtBP/BARS) related protein. AN is expressed at low levels in all organs and the AN protein is localized in the cytoplasm. In an mutant trichomes, the organization of the actin cytoskeleton is normal but the distribution of microtubules is aberrant. A role of AN in the control of the microtubule cytoskeleton is further supported by the finding that AN genetically and physically interacts with ZWICHEL, a kinesin motor molecule involved in trichome branching. Our data suggest that CtBP/BARS-like protein function in plants is directly associated with the microtubule cytoskeleton.

CPR5 is involved in cell proliferation and cell death control and encodes a novel transmembrane protein

Plants often respond to pathogens by sacrificing cells at the infection site. This type of programmed cell death is mimicked by the constitutive pathogene response5 (cpr5) mutant in Arabidopsis in the absence of pathogens, suggesting a role for CPR5 in programmed cell death control. The analysis of the cellular phenotypes of two T-DNA-tagged cpr5 alleles revealed an additional role for CPR5 in the regulation of endoreduplication and cell division. In cpr5 mutant trichomes, endoreduplication cycles stop after two rounds instead of four, and trichome cells have fewer branches than normal. Eventually, cpr5 trichomes die, the nucleus disintegrates, and the cell collapses. Similarly, leaf growth stops earlier than in wild-type, and, frequently, regions displaying spontaneous cell death are observed. The cloning of the CPR5 gene revealed a novel putative transmembrane protein with a cytosolic domain containing a nuclear-targeting sequence. The dual role of CPR5 in cell proliferation and cell death control suggests a regulatory link between these two processes.

Parthenogenetic egg cells of wheat: cellular and molecular studies

The 'Salmon' system of wheat comprises three isogenic alloplasmic lines with either zygotic (aS) or autonomous, fertilisation-independent (cS kS) embryo development. While the initiation of embryogenesis from the isolated sexual egg cell depends on in vitro fertilisation, the corresponding parthenogenetic egg cell develops into an early embryo without fertilisation. This demonstrates that parthenogenesis is an inherent feature of the isolated egg cell. Based on this observation, we have constructed egg-cell-specific cDNA libraries and report first results of a sequencing project aimed at the isolation of putative egg-cell-specific and parthenogenesis-related genes.

Cell polarity in Arabidopsis trichomes

Arabidopsis leaf trichomes are unicellular hairs that display a highly characteristic cell form that has a fixed orientation with respect to the basal-distal leaf axis. The genetic, molecular and cell biological analysis of trichome morphogenesis reveal that various cellular processes need to be coordinated including regulation of the cell cycle, the cell size and the actin and tubulin cytoskeleton. Here we will focus on what is known about the establishment and maintenance of positional information during trichome formation.

Ectopic expression of the Arabidopsis AtMYB23 gene induces differentiation of trichome cells

The control of epidermal cell fate is a complex molecular process and requires the regulatory activity of different transcription factors. Here, we describe the isolation of a member of the Arabidopsis MYB transcription factor family, AtMYB23, that is involved in trichome development. Expression of the AtMYB23 gene under the control of the viral CaMV 35S promoter causes the development of ectopic trichomes. The formation of ectopic trichomes depends on TRANSPARENT TESTA GLABRA1 but not on GLABRA1. The absence of the negative regulator TRIPTYCHON leads to branching of the ectopic trichomes on cotyledons and the formation of ectopic trichomes in the leaf subepidermal cell layer. The CaMV 35S promoter-controlled expression of AtMYB23 can partially rescue the glabra1 mutant phenotype. Together, the presented data indicate that the AtMYB23 gene has partially overlapping functions with GLABRA1 in controlling the initiation of trichome development.

FUSCA3 encodes a protein with a conserved VP1/AB13-like B3 domain which is of functional importance for the regulation of seed maturation in Arabidopsis thaliana

Conditionally lethal mutant alleles of the FUSCA3 (FUS3) gene of Arabidopsis thaliana are specifically defective in the gene expression program responsible for seed maturation. FUS3 was isolated by map-based cloning and expression of the FUS3 cDNA resulted in complementation of the Fus3- phenotype. In the predicted FUS3 gene product, a continuous stretch of more than 100 amino acids shows significant sequence similarity to the B3 domains of the polypeptides encoded by ABI3 (Arabidopsis) and VP1 (maize). FUS3 transcription was detected mainly in siliques and was found to be developmentally regulated during embryogenesis. Transcripts of abnormal sizes were observed in fus3 mutants due to aberrant splicing caused by point mutations at intron termini. Sequence analysis of mutant and wild-type FUS3 alleles, as well as sequencing of fus3 cDNAs, revealed small inframe deletions at two different sites of the coding region. While a deletion between B3 and the C-terminus of the predicted polypeptide was found in conjunction with normal FUS3 function, another deletion located within the conserved B3 domain (as well as truncations therein) were associated with the Fus3- phenotype. It is apparent, therefore, that an intact B3 domain is essential for the regulation of seed maturation by FUS3.

Two novel MYB homologues with changed expression in late embryogenesis-defective Arabidopsis mutants

Two novel MYB genes (ATMYBR1 and ATMYBR2) were isolated from Arabidopsis thaliana. Binding to a conserved MYB recognition sequence is demonstrated for the ATMYBR1 protein. The expression of both genes is affected by the fus3, lec1 and abi3 mutations causing pleiotropic defects during late embryogenesis and seed maturation including the loss of dormancy and desiccation tolerance. The strong increase of the transcript levels of both MYB genes during very late stages of embryogenesis typically found in wild type is missing in the mutants. Furthermore, the expression of both MYB genes is developmentally regulated in vegetative tissues. The highly conserved repeats (R2 and R3) of the DNA binding MYB domain of both proteins represent chimeric structures combining features typical of plant and animal derived proteins. This demonstrates the existence of a distinct subfamily of animal-like MYB factors in plant genomes.

Ectopic expression of a novel MYB gene modifies the architecture of the Arabidopsis inflorescence

The Arabidopsis thaliana mutants fus3, lec1 and abi3 have pleiotropic defects during late embryogenesis. Mutant embryos fail to enter the maturation programme and initiate a vegetative germination pathway instead. Screening for genes which are differentially expressed in the fus3 mutant of Arabidopsis resulted in the isolation of several members of the MYB family. MYB domain proteins in plants represent an extended gene family of transcription factors, suggesting their participation in a variety of plant specific cellular functions. Here, the authors describe one of these genes, designated AtMYB13, representing a novel member of the MYB gene family. The structure of the gene as well as its genomic organisation and localisation are reported. The expression of the gene is regulated by dehydration, exogenous abscisic acid, light and wounding. A chimeric AtMYB13 promoter/GUS gene is tissue-specifically expressed in transgenic Arabidopsis plants. The GUS staining was predominantly detected in the shoot apex zone and at the basis of developing flowers. In addition, the AtMYB13 gene promoter is active at branching points of the inflorescence. Furthermore, ectopic expression of the AtMYB13 gene has a characteristic impact on the architecture of the inflorescence leading to peculiar hook structures at pedicel branching points. In addition, some transgenic plants exhibit a reversed order of first flowers and axillary buds. These data suggest a function of the AtMYB13 gene product in linking shoot morphogenic activity with environmental as well as intrinsic signals.

A novel leaf-specific myb-related protein with a single binding repeat

A novel myb-like gene (AtmybL2) was isolated from an Arabidopsis thaliana cDNA library. The single copy gene was localised on chromosome I. A gene specific transcript is preferentially found in leaves. The predicted gene product consists of a conservative N-terminal myb-domain known to be involved in DNA-binding and a unique proline-rich C-terminal part. Remarkably, the myb-domain includes only one of the typical two or three tryptophan repeats found in other myb-like proteins.

Two new oleosin isoforms with altered expression patterns in seeds of the Arabidopsis mutant fus3

Oleosins are proteins associated with lipid bodies mainly synthesised during seed development. Using a subtractive hybridisation approach two new members of the oleosin gene family of Arabidopsis thaliana have been isolated. The quantitative and temporal expression patterns of both genes are found to be affected in the fus3 mutant defective in late embryogenesis. This pattern is interpreted as a molecular marker for a mutant specific developmental change from a seed maturation to a germination pathway.