PubMed Health⌕ Search

Biomedical subjects

Christian Dumas

Publications and source records attributed to Christian Dumas.

At least 19 recordsLinked to original sources
PubMed2006

BIGPETALp, a bHLH transcription factor is involved in the control of Arabidopsis petal size.

In Arabidopsis, APETALA1, PISTILLATA, APETALA3 and SEPALLATA interact to form multimeric protein complexes required to specify petal identity. However, the downstream events that lead to petal specific shape and size remain largely unknown. Organ final size can be influenced by cell number or cell expansion or both. To date, no gene that specifically limits petal size by controlling postmitotic cell expansion has been identified. Here we have identified a novel petal-expressed, basic helix-loop-helix encoding gene (BIGPETAL, BPE) that is involved in the control of petal size. BPE is expressed via two mRNAs derived from an alternative splicing event. The BPEub transcript is expressed ubiquitously, whereas the BPEp transcript is preferentially expressed in petals. We demonstrate that BPEp is positively regulated downstream of APETALA3, PISTILLATA, APETALA1 and PISTILLATA3 and is negatively regulated downstream of AGAMOUS. Plants that lack the petal-expressed variant BPEp have larger petals as a result of increased cell size, showing that BPEp interferes with postmitotic cell expansion. BPEp is therefore a part of the network that links the patterning genes to final morphogenesis.

Alternative Splicing↗
PubMed2006

An evolutionary perspective on the regulation of carpel development.

The carpel, or female reproductive organ enclosing the ovules, is one of the major evolutionary innovations of the flowering plants. The control of carpel development has been intensively studied in the model eudicot species Arabidopsis thaliana. This review traces the evolutionary history of genes involved in carpel development by surveying orthologous genes in taxa whose lineages separated from that of A. thaliana at different levels of the phylogenetic tree of the seed plants. Some aspects of the control of female reproductive development are conserved between the flowering plants and their sister group, the gymnosperms, indicating the presence of these in the common ancestor of the extant seeds plants, some 300 million years ago. Gene duplications that took place in the pre-angiosperm lineage, before the evolution of the first flowering plants, provided novel gene clades of potential importance for the origin of the carpel. Subsequent to the appearance of the first flowering plants, further gene duplications have led to sub-functionalization events, in which pre-existing reproductive functions were shared between paralogous gene clades. In some cases, fluidity in gene function is evident, leading to similar functions in carpel development being controlled by non-orthologous genes in different taxa. In other cases, gene duplication events have created sequences that evolved novel functions by the process of neo-functionalization, thereby generating biodiversity in carpel and fruit structures.

Biological Evolution↗
PubMed2006

Fertilization in plants: is calcium a key player?

For many years, the physiological significance of Ca(2+) oscillations has been a matter of debate, but the potential to encode and transduce information in the pattern of an oscillation is obvious. In this review, we only consider transients and oscillations observed during fertilization in plants with the major focus on flowering plants. After presenting data related to algae, fertilization mechanisms in flowering plants are defined as a multi-step phenomenon, starting with pollination during which calcium plays a key role, especially during pollen-stigma interactions (compatible and incompatible reactions). The pollen tube serves as a guide and a pathway for the sperm cells on their course towards their female target cells. For many years, the pollen tube has also been studied as an easily accessible in vitro model to elucidate the role of calcium on tip growth. Finally, in flowering plants, a unique double fertilization system is present. Interesting data obtained from an in vitro fertilization system in maize are presented and discussed. In addition, the new approaches made possible by Arabidopsis and Torenia and their potential limitations are covered.

Arabidopsis↗
PubMed2005

Role of petal-specific orcinol O-methyltransferases in the evolution of rose scent.

Orcinol O-methyltransferase (OOMT) 1 and 2 catalyze the last two steps of the biosynthetic pathway leading to the phenolic methyl ether 3,5-dimethoxytoluene (DMT), the major scent compound of many rose (Rosa x hybrida) varieties. Modern roses are descended from both European and Chinese species, the latter being producers of phenolic methyl ethers but not the former. Here we investigated why phenolic methyl ether production occurs in some but not all rose varieties. In DMT-producing varieties, OOMTs were shown to be localized specifically in the petal, predominantly in the adaxial epidermal cells. In these cells, OOMTs become increasingly associated with membranes during petal development, suggesting that the scent biosynthesis pathway catalyzed by these enzymes may be directly linked to the cells' secretory machinery. OOMT gene sequences were detected in two non-DMT-producing rose species of European origin, but no mRNA transcripts were detected, and these varieties lacked both OOMT protein and enzyme activity. These data indicate that up-regulation of OOMT gene expression may have been a critical step in the evolution of scent production in roses.

Amino Acid Sequence↗
PubMed2005

Structure of a liganded type 2 non-specific lipid-transfer protein from wheat and the molecular basis of lipid binding.

In plants, a family of ubiquitous proteins named non-specific lipid-transfer proteins (ns-LTPs) facilitates the transfer of fatty acids, phospholipids and steroids between membranes. Recent data suggest that these secreted proteins play a key role in the formation of cuticular wax layers and in defence mechanisms against pathogens. In this study, X-ray crystallography has been used to examine the structural details of the interaction between a wheat type 2 ns-LTP and a lipid, L-alpha-palmitoyl-phosphatidyl glycerol. This crystal structure was solved ab initio at 1.12 A resolution by direct methods. The typical alpha-helical bundle fold of this protein is maintained by four disulfide bridges and delineates two hydrophobic cavities. The inner surface of the main cavity is lined by non-polar residues that provide a hydrophobic environment for the palmitoyl moiety of the lipid. The head-group region of this lipid protrudes from the surface and makes several polar interactions with a conserved patch of basic residues at the entrance of the pocket. The alkyl chain of a second lipid is bound within an adjacent smaller cavity. The structure shows that binding of the lipid tails to the protein involves extensive hydrophobic interactions.

Amino Acid Sequence↗
PubMed2005

Evidence that CRABS CLAW and TOUSLED have conserved their roles in carpel development since the ancestor of the extant angiosperms.

The carpel is the female reproductive organ specific to flowering plants. We aim to define the genes that controlled carpel development in the common ancestor of this group as a step toward determining the molecular events that were responsible for the evolution of the carpel. CRABS CLAW (CRC) and TOUSLED (TSL) control important aspects of carpel development in the model plant, Arabidopsis thaliana. The basal angiosperm species Amborella trichopoda and Cabomba aquatica very likely represent the two most early diverging groups of flowering plants. We have identified putative orthologues of CRC and TSL from A. trichopoda and C. aquatica, respectively. We demonstrate the expression patterns of these genes in carpels to be very highly conserved, both spatially and temporally, with those of their Arabidopsis orthologues. We argue that CRC and TSL in Arabidopsis are likely to have conserved their respective roles in carpel development since the common ancestor of the living flowering plants. We conclude that a divergent role shown for the CRC orthologue in rice, DROOPING LEAF, most probably arose specifically in the monocot lineage. We show that, in addition to its expression in carpels, the TSL orthologue of C. aquatica is expressed in tissues that contribute to buoyancy and argue that its role in these tissues may have arisen later than its role in carpel development.

Arabidopsis↗
PubMed2005

Multicellular structures developing during maize microspore culture express endosperm and embryo-specific genes and show different embryogenic potentialities.

During maize pollen embryogenesis, a range of multicellular structures are formed. Using different approaches, the "nature" of these structures has been determined in terms of their embryogenic potential. In situ molecular identification techniques for gene transcripts and products, and a novel cell tracking system indicated the presence of embryogenic (embryo-like structures, ELS) and non-embryogenic (callus-like structures, CLS) structures that occurred for short periods within the cultures. Some multicellular structures with a compact appearance generated embryos. RT-PCR and fluorescence in situ hybridization (FISH) with confocal microscopy techniques using specific gene markers of the endosperm (ZmESR2, ZmAE3) and embryo (LTP2 and ZmOCL1, ZmOCL3) revealed "embryo" and "endosperm" potentialities in these various multicellular structures present in the cultures. The results presented here showed distinct and specific patterns of gene expression. Altogether, the results demonstrate the presence of different molecules on both embryonic and non-embryonic structures. Their possible roles are discussed in the context of a parallel between embryo/endosperm interactions in planta and embryonic and non-embryonic structure interrelations under in vitro conditions.

Biomarkers↗
PubMed2004

Structure of the mature P3-virus particle complex of cauliflower mosaic virus revealed by cryo-electron microscopy.

The cauliflower mosaic virus (CaMV) has an icosahedral capsid composed of the viral protein P4. The viral product P3 is a multifunctional protein closely associated with the virus particle within host cells. The best-characterized function of P3 is its implication in CaMV plant-to-plant transmission by aphid vectors, involving a P3-virion complex. In this transmission process, the viral protein P2 attaches to virion-bound P3, and creates a molecular bridge between the virus and a putative receptor in the aphid's stylets. Recently, the virion-bound P3 has been suggested to participate in cell-to-cell or long-distance movement of CaMV within the host plant. Thus, as new data accumulate, the importance of the P3-virion complex during the virus life-cycle is becoming more and more evident. To provide a first insight into the knowledge of the transmission process of the virus, we determined the 3D structures of native and P3-decorated virions by cryo-electron microscopy and computer image processing. By difference mapping and biochemical analysis, we show that P3 forms a network around the capsomers and we propose a structural model for the binding of P3 to CaMV capsid in which its C terminus is anchored deeply in the inner shell of the virion, while the N-terminal extremity is facing out of the CaMV capsid, forming dimers by coiled-coil interactions. Our results combined with existing data reinforce the hypothesis that this coiled-coil N-terminal region of P3 could coordinate several functions during the virus life-cycle, such as cell-to-cell movement and aphid-transmission.

Caulimovirus↗
PubMed2004

High-resolution X-ray structure of the unexpectedly stable dimer of the [Lys(-2)-Arg(-1)-des(17-21)]endothelin-1 peptide.

Previous structural studies on the [Lys((-2))-Arg((-1))]endothelin-1 peptide (KR-ET-1), 540-fold less potent than ET-1, strongly suggested the presence of an intramolecular Arg(-1)-Asp(8) (R(-1)-D(8)) salt bridge that was also observed in the shorter [Lys((-2))-Arg((-1))-des(17-21)]endothelin-1 derivative (KR-CSH-ET). In addition, for these two analogues, we have shown that the Lys-Arg dipeptide, which belongs to the prosequence, significantly improves the formation of the native disulfide bonds (>or=96% instead of approximately 70% for ET-1). In contrast to what was inferred from NMR data, molecular dynamics simulations suggested that such an intramolecular salt bridge would be unstable. The KR-CSH-ET peptide has now been crystallized at pH 5.0 and its high-resolution structure determined ab initio at 1.13 A using direct methods. Unexpectedly, KR-CSH-ET was shown to be a head-to-tail symmetric dimer, and the overall interface involves two intermolecular R(-1)-D(8) salt bridges, a two-stranded antiparallel beta-sheet, and hydrophobic contacts. Molecular dynamics simulations carried out on this dimer clearly showed that the two intermolecular salt bridges were in this case very stable. Sedimentation equilibrium experiments unambiguously confirmed that KR-ET-1 and KR-CSH-ET also exist as dimers in solution at pH 5.0. On the basis of the new dimeric structure, previous NMR data were reinterpreted. Structure calculations were performed using 484 intramolecular and 38 intermolecular NMR-derived constraints. The solution and the X-ray structures of the dimer are very similar (mean rmsd of 0.85 A). Since the KR dipeptide at the N-terminus of KR-CSH-ET is present in the prosequence, it can be hypothesized that similar intermolecular salt bridges could be involved in the in vivo formation of the native disulfide bonds of ET-1. Therefore, it appears to be likely that the prosequence does assist the ET-1 folding in a chaperone-like manner before successive cleavages that yield the bioactive ET-1 hormone.

Amino Acid Sequence↗
PubMed2004

Crystallization and preliminary crystallographic studies of MOMP (major outer membrane protein) from Campylobacter jejuni.

Campylobacter jejuni is the leading bacterial cause of human enteritis linked to ingestion of contaminated food or water. MOMP, the major outer membrane protein from these Gram-negative bacteria, belongs to the porin family. In order to determine the three-dimensional structure of this protein and to elucidate the underlying molecular mechanisms, the MOMP from C. jejuni strain 85H has been purified and crystallized by vapour diffusion. Two crystal forms were characterized for this membrane protein. X-ray diffraction data were collected to a resolution of 3.1 A using a synchrotron-radiation source from the orthorhombic crystal form, which belonged to space group P2(1)2(1)2 with unit-cell parameters a = 170.1, b = 101.9, c = 104.9 A. With a trimer in the asymmetric unit, the solvent content is 64% (V(M) = 3.4 A Da(-1)). The other form exhibits trigonal symmetry (space group R3) with hexagonal unit-cell parameters a = b = 94.2, c = 161.2 A, but diffracts X-rays poorly to about 4 A with significant anisotropy.

Bacterial Proteins↗
PubMed2004

A W-box is required for full expression of the SA-responsive gene SFR2.

Transcripts of SFR2, a member of the S family of receptor kinase genes, accumulate rapidly in Brassica oleracea leaves in response to wounding, bacterial infection and following treatment with salicylic acid (SA). Expression of a chimeric gene consisting of the SFR2 5' flanking sequence fused to the gusA reporter gene is also induced in wounded and SA-treated Arabidopsis plants indicating that the observed response is conferred by the SFR2 promoter. We show here that, in Arabidopsis plants carrying the salicylate hydroxylase (NahG) transgene, wound induction of the SFR2 promoter-gusA reporter fusion was abolished, indicating that, as has previously been shown for the response to bacterial infection, SA is required for the response to wounding. Deletion analysis of the SFR2 promoter identified a region necessary for full expression following SA treatment. This region, which includes two putative W-boxes, is conserved in the promoter of the Arabidopsis SFR2 homologue, ARK3. Deletion of a 12 bp region containing the two W-box motifs reduced the response to SA treatment. Tandem repeats of the W-box-containing element fused upstream of a CaMV 35S minimal promoter enhanced reporter gene expression in transgenic Arabidopsis both in the absence and presence of SA. Gel-mobility shift assays showed that Arabidopsis leaf extracts contained factors that bound to a fragment of the promoter spanning the putative W-boxes and that a fragment in which these motifs were mutated was unable to compete for binding. In summary, induction of the SFR2 promoter in response to bacterial infection and wounding requires SA, and full expression of the induced gene requires the presence of a functional element containing W-box motifs in the SFR2 promoter. The involvement of two W-boxes indicates that transcription factors of the WRKY family may play a key role in mediating these responses.

Arabidopsis↗
PubMed2004

Crystal structure of the coiled-coil dimerization motif of geminin: structural and functional insights on DNA replication regulation.

We have determined the crystal structure of the coiled-coil domain of human geminin, a DNA synthesis inhibitor in higher eukaryotes. We show that a peptide encompassing the five heptad repeats of the geminin leucine zipper (LZ) domain is a dimeric parallel coiled coil characterized by a unique pattern of internal polar residues and a negatively charged surface that may target the basic domain of interacting partners. We show that the LZ domain itself is not sufficient to inhibit DNA synthesis but upstream and downstream residues are required. Analysis of a functional form of geminin by density sedimentation indicates an oligomeric structure. X-ray solution scattering experiments performed on a non-functional form of geminin having upstream basic residues and the LZ domain show a tetramer structure. Altogether, these results give a consistent identification and mapping of geminin interacting regions onto structurally important domains. They also suggest that oligomerization properties of geminin may be implicated in its inhibitory activity of DNA synthesis.

Amino Acid Sequence↗
PubMed2004

NMR solution structure of Mob1, a mitotic exit network protein and its interaction with an NDR kinase peptide.

Proteins of the Mob1/phocein family are found in all eukaryotic cells. In yeast, they are activating subunits of Dbf2-related protein kinases involved in cell cycle control. Despite the wide occurrence of these proteins, their biological functions remain poorly understood. Here we report the solution structure of the Mob1 protein from Xenopus laevis solved by heteronuclear multidimensional NMR. The structure reveals a fold constituted by a central left-handed four-helix bundle, one connecting helix, two flanking helices and a long flexible loop. The clustering of two Cys and two His residues, and zinc measurement by atomic absorption spectroscopy support the existence of a zinc ion binding site. Our NMR structure is in good agreement with the recently described X-ray structure of human Mob1-A. Chemical shift perturbations observed upon addition of a peptide encompassing the basic region of the N-terminal regulatory domain of NDR kinase were used to identify and map a specific interaction between Mob1 and this kinase. The chemical shift changes indicate that the main interaction occurs on the acidic and conserved surface of Mob1. This surface was previously hypothesized to be the interaction surface according to the X-ray structure and was identified as functionally important in yeast. Our data suggest that the NDR kinase is a functional Dbf2 homologue in animal cells and contributes to the understanding of the molecular function of Mob1 proteins.

Amino Acid Sequence↗
PubMed2004

Morphogenesis of maize embryos requires ZmPRPL35-1 encoding a plastid ribosomal protein.

In emb (embryo specific) mutants of maize (Zea mays), the two fertilization products have opposite fates: Although the endosperm develops normally, the embryo shows more or less severe aberrations in its development, resulting in nonviable seed. We show here that in mutant emb8516, the development of mutant embryos deviates as soon as the transition stage from that of wild-type siblings. The basic events of pattern formation take place because mutant embryos display an apical-basal polarity and differentiate a protoderm. However, morphogenesis is strongly aberrant. Young mutant embryos are characterized by protuberances at their suspensor-like extremity, leading eventually to structures of irregular shape and variable size. The lack of a scutellum or coleoptile attest to the virtual absence of morphogenesis at the embryo proper-like extremity. Molecular cloning of the mutation was achieved based on cosegregation between the mutant phenotype and the insertion of a MuDR element. The Mu insertion is located in gene ZmPRPL35-1, likely coding for protein L35 of the large subunit of plastid ribosomes. The isolation of a second allele g2422 and the complementation of mutant emb8516 with a genomic clone of ZmPRPL35-1 confirm that a lesion in ZmPRPL35-1 causes the emb phenotype. ZmPRPL35-1 is a low-copy gene present at two loci on chromosome arms 6L and 9L. The gene is constitutively expressed in all major tissues of wild-type maize plants. Lack of expression in emb/emb endosperm shows that endosperm development does not require a functional copy of ZmPRPL35-1 and suggests a link between plastids and embryo-specific signaling events.

Amino Acid Sequence↗
PubMed2004

Characterization of proteins secreted during maize microspore culture: arabinogalactan proteins (AGPs) stimulate embryo development.

To study molecules secreted from cultured plant cells that promote development, maize microspores were transferred into culture and the conditioned media were collected over time and analysed. Electrophoresis indicated that both non-glycosylated and glycosylated proteins including arabinogalactan proteins (AGPs) appeared in the medium and their concentration increased during the time of culture. The development of embryos was correlated with the presence of specific extracellular proteins, using an experimental system based on a tunicamycin inhibition test. In addition, a precise protein analysis was conducted using MALDI-TOF and ESI-MS-MS techniques. These approaches have allowed the identification of 5 other types of proteins: a cell wall invertase, two thaumatin isoforms, one 1-3 beta-glucanase and two chitinase isoforms. Altogether these experiments and results open ways for research aimed at understanding which molecules stimulate embryo formation. Moreover, AGPs may be used to stimulate the development of microspores (pollen embryogenesis) prepared from non-responsive genotypes.

Culture Media, Conditioned↗
PubMed2003

Crystal structure of the N-terminal dimerisation domain of VicH, the H-NS-like protein of Vibrio cholerae.

The histone-like nucleoid structuring (H-NS) protein is a global modulator of gene expression in Gram-negative bacteria. VicH, the H-NS protein of Vibrio cholerae, regulates the expression of certain major virulence determinants implicated in the pathogenesis of cholera. We present here the 2.5A crystal structure of the N-terminal oligomerisation domain of VicH (VicH_Nt). VicH_Nt adopts the same fold and dimeric assembly as the NMR structure of Escherichia coli H-NS_Nt, thus validating this fold against conflicting data. The structural similarity of V.cholerae VicH_Nt and E.coli H-NS_Nt, despite differences in origin, system of expression, experimental conditions and techniques used, indicates that the fold determined in our studies is robust to experimental conditions. Structural analysis and homology modelling were carried out to further elucidate the molecular basis of the functional polyvalence of the N-terminal domain. Our analysis of members of the H-NS superfamily supports the suggestion that the oligomerisation function of H-NS_Nt is conserved even in more distantly related proteins.

Amino Acid Sequence↗
PubMed2003

The identification of candidate genes for a reverse genetic analysis of development and function in the Arabidopsis gynoecium.

The screening for mutants and their subsequent molecular analysis has permitted the identification of a number of genes of Arabidopsis involved in the development and functions of the gynoecium. However, these processes remain far from completely understood. It is clear that in many cases, genetic redundancy and other factors can limit the efficiency of classical mutant screening. We have taken the alternative approach of a reverse genetic analysis of gene function in the Arabidopsis gynoecium. A high-throughput fluorescent differential display screen performed between two Arabidopsis floral homeotic mutants has permitted the identification of a number of genes that are specifically or preferentially expressed in the gynoecium. Here, we present the results of this screen and a detailed characterization of the expression profiles of the genes identified. Our expression analysis makes novel use of several Arabidopsis floral homeotic mutants to provide floral organ-specific gene expression profiles. The results of these studies permit the efficient targeting of effort into a functional analysis of gynoecium-expressed genes.

Arabidopsis↗