The MIR396 family, composed of ath‐miR396a and ath‐miR396b in Arabidopsis, is conserved among plant species and is known to target the Growth‐Regulating Factor (GRF) gene family. ath‐miR396 overexpressors or grf mutants are characterised...
moreThe MIR396 family, composed of ath‐miR396a and ath‐miR396b in Arabidopsis, is conserved among plant species and is known to target the Growth‐Regulating Factor (GRF) gene family. ath‐miR396 overexpressors or grf mutants are characterised by small and narrow leaves and show embryogenic defects such as cotyledon fusion. Heterologous expression of ath‐miR396a has been reported in tobacco and resulted in reduction of the expression of three NtGRF genes. In this study, the precursor of the Populus trichocarpa ptc‐miR396c, with a mature sequence identical to ath‐miR396b, was expressed under control of the CaMV35S promoter in tobacco. Typical phenotypes of GRF down‐regulation were observed, including cotyledon fusion and lack of shoot apical meristem (SAM). At later stage of growth, transgenic plants had delayed development and altered specification of organ type during flower development. The third and fourth whorls of floral organs were modified into stigmatoid anthers and fasciated carp...
REALLY INTERESTING NEW GENE (RING) proteins play important roles in the regulation of many processes by recognizing target proteins for ubiquitination. Previously, we have shown that the expression of PtaRHE1, encoding a Populus...
moreREALLY INTERESTING NEW GENE (RING) proteins play important roles in the regulation of many processes by recognizing target proteins for ubiquitination. Previously, we have shown that the expression of PtaRHE1, encoding a Populus tremula × Populus alba RING-H2 protein with E3 ubiquitin ligase activity, is associated with tissues undergoing secondary growth. To further elucidate the role of PtaRHE1 in vascular tissues, we have undertaken a reverse genetic analysis in poplar. Within stem secondary vascular tissues, PtaRHE1 and its corresponding protein are expressed predominantly in the phloem. The downregulation of PtaRHE1 in poplar by artificial miRNA triggers alterations in phloem fibre patterning, characterized by an increased portion of secondary phloem fibres that have a reduced cell wall thickness and a change in lignin composition, with lower levels of syringyl units as compared with wild-type plants. Following an RNA-seq analysis, a biological network involving hormone stress signalling, as well as developmental processes, could be delineated. Several candidate genes possibly associated with the altered phloem fibre phenotype observed in amiRPtaRHE1 poplar were identified. Altogether, our data suggest a regulatory role for PtaRHE1 in secondary phloem fibre development.
Cinnamyl alcohol dehydrogenase (CAD) catalyzes the last step in the biosynthesis of the lignin precursors, the monolignols. We have down-regulated CAD in transgenic poplar (Populus tremula X Populus alba) by both antisense and...
moreCinnamyl alcohol dehydrogenase (CAD) catalyzes the last step in the biosynthesis of the lignin precursors, the monolignols. We have down-regulated CAD in transgenic poplar (Populus tremula X Populus alba) by both antisense and co-suppression strategies. Several antisense and sense CAD transgenic poplars had an approximately 70% reduced CAD activity that was associated with a red coloration of the xylem tissue. Neither the lignin amount nor the lignin monomeric composition (syringyl/guaiacyl) were significantly modified. However, phloroglucinol-HCl staining was different in the down-regulated CAD plants, suggesting changes in the number of aldehyde units in the lignin. Furthermore, the reactivity of the cell wall toward alkali treatment was altered: a lower amount of lignin was found in the insoluble, saponified residue and more lignin could be precipitated from the soluble alkali fraction. Moreover, large amounts of phenolic compounds, vanillin and especially syringaldehyde, were de...
To improve the digestibility of the forage crop alfalfa (Medicago sativa L.), cinnamyl alcohol dehydrogenase (CAD), which catalyses the last step in the biosynthesis of the lignin monomers, was down-regulated by using an antisense...
moreTo improve the digestibility of the forage crop alfalfa (Medicago sativa L.), cinnamyl alcohol dehydrogenase (CAD), which catalyses the last step in the biosynthesis of the lignin monomers, was down-regulated by using an antisense approach. A subset of six transgenic lines with reduced CAD activity and control lines were analysed when grown in the greenhouse and in the field. The down-regulation of the CAD enzyme was associated with a red coloration of the stem. The lignin quantity remained unchanged, but the lignin composition, as determined by thioacidolysis, was altered. The highest reduction of CAD activity was associated with a lower syringyl/guaiacyl (S/G) ratio and a lower S+G yield, mainly because of a decreased amount of S units. An increase in in situ disappearance of dry matter and of cell wall residue was detected in one of the transgenic lines grown in the greenhouse, and for two of the lines grown in the field the rate of disappearance of dry matter slightly improved. ...
... C. Lapierre, B. Pollet, M. Petit-Conil, G. Toval, J. Romero, G. Pilate, J.-C. Lepl6, W. Boerjan, V. Ferret, V. De Nadai & L. Jouanin, Structural alterations of lignins in transgenic poplars with depressed cinnamyl alcohol...
more... C. Lapierre, B. Pollet, M. Petit-Conil, G. Toval, J. Romero, G. Pilate, J.-C. Lepl6, W. Boerjan, V. Ferret, V. De Nadai & L. Jouanin, Structural alterations of lignins in transgenic poplars with depressed cinnamyl alcohol dehydrogenase or caffeic acid O-methyltransferase activity ...
For the production of high-quality paper, lignin needs to be removed from cellulose. This process is energy requiring, expensive and toxic. Molecular biology offers tools to generate trees with a modified lignin composition to facilitate...
moreFor the production of high-quality paper, lignin needs to be removed from cellulose. This process is energy requiring, expensive and toxic. Molecular biology offers tools to generate trees with a modified lignin composition to facilitate the extractability of lignin. We have cloned several genes encoding enzymes in the methylation of the lignin monomers [bi-specific caffeic acid/5-hydroxyferulic acidO-methyltransferase (COMT) and caffeoyl-CoAO-methyltransferase],
Lignin is a heterogenous phenolic polymer that plays crucial roles in the development and physiology of vascular plants. However, it needs to be removed from cellulose by toxic and energy-requiring processes for the production of...
moreLignin is a heterogenous phenolic polymer that plays crucial roles in the development and physiology of vascular plants. However, it needs to be removed from cellulose by toxic and energy-requiring processes for the production of high-quality paper. Therefore, a major biotechnological challenge is to obtain transgenic trees with modified lignin to improve the quality of wood for paper making. Here,
RING (REALLY INTERESTING NEW GENE) proteins with E3 ligase activity are largely represented in plants. They have been shown to play important roles in the regulation of many biological processes by recognizing target proteins for...
moreRING (REALLY INTERESTING NEW GENE) proteins with E3 ligase activity are largely represented in plants. They have been shown to play important roles in the regulation of many biological processes by recognizing target proteins for ubiquitination. PtaRHE1, encoding a poplar RING-H2 domain-containing protein with E3 ligase activity has been previously shown to be expressed during the establishment of secondary vascular system in poplar. In the present report, we demonstrate that the expression of PtaRHE1 and the accumulation of its corresponding protein are modulated by the relative atmospheric and soil humidity and by abscisic acid. Overall, the integrated data are discussed within a working model highlighting a plausible function of PtaRHE1 in the signaling and/or in the regulation of water status in poplar.
The MIR396 family, composed of ath-miR396a and ath-miR396b in Arabidopsis, is conserved among plant species and is known to target the Growth-Regulating Factor (GRF) gene family. ath-miR396 overexpressors or grf mutants are characterised...
moreThe MIR396 family, composed of ath-miR396a and ath-miR396b in Arabidopsis, is conserved among plant species and is known to target the Growth-Regulating Factor (GRF) gene family. ath-miR396 overexpressors or grf mutants are characterised by small and narrow leaves and show embryogenic defects such as cotyledon fusion. Heterologous expression of ath-miR396a has been reported in tobacco and resulted in reduction of the expression of three NtGRF genes. In this study, the precursor of the Populus trichocarpa ptc-miR396c, with a mature sequence identical to ath-miR396b, was expressed under control of the CaMV35S promoter in tobacco. Typical phenotypes of GRF down-regulation were observed, including cotyledon fusion and lack of shoot apical meristem (SAM). At later stage of growth, transgenic plants had delayed development and altered specification of organ type during flower development. The third and fourth whorls of floral organs were modified into stigmatoid anthers and fasciated carpels, respectively. Several NtGRF genes containing a miR396 binding site were found to be down-regulated, and the cleavage of their corresponding mRNA at the miR396 binding site was confirmed for two of them using RACE-PCR analysis. The data obtained agree with the functional conservation of the miR396 family in plants and suggest a role for the miR396/GRF network in determination of floral organ specification.
Vascular tissue differentiation is essential to enable plant growth and follows well-structured and complex developmental patterns. Based on recent data obtained from Arabidopsis and Populus, advances in the understanding of the molecular...
moreVascular tissue differentiation is essential to enable plant growth and follows well-structured and complex developmental patterns. Based on recent data obtained from Arabidopsis and Populus, advances in the understanding of the molecular basis of vascular system development are reviewed. As identified by forward and/or reverse genetics, several gene families have been shown to be involved in the proliferation and identity of vascular tissues and in vascular bundle patterning. Although the functioning of primary meristems, for example the shoot apical meristem (SAM), is well documented in the literature, the genetic network that regulates (pro)cambium is still largely not deciphered. However, recent genome-wide expression analyses have identified candidate genes for secondary vascular tissue development. Of particular interest, several genes known to regulate the SAM have also been found to be expressed in the vascular cambium, highlighting possible overlapping regulatory mechanisms between these two meristems.
O-Methyltransferases (OMT; EC 2.1.1.6) play an important role in the synthesis of lignin precursors by catalyzing the O-methylation of o-diphenolic substrates such as caffeic acid (CA) and 5-hydroxyferulic acid (5OH). Here, we report on...
moreO-Methyltransferases (OMT; EC 2.1.1.6) play an important role in the synthesis of lignin precursors by catalyzing the O-methylation of o-diphenolic substrates such as caffeic acid (CA) and 5-hydroxyferulic acid (5OH). Here, we report on the purification of a lignin-specific OMT (38 kDa) from poplar (Populus trichocarpa x P. deltoides). The OMT was purified from xylem by a single affinity chromatography step on adenosine agarose. The enzyme uses both CA and 5OH as substrates. We previously have reported the cloning of a corresponding OMT cDNA [Dumas et al., Plant Physiol. 98 (1992) 796-797]. Expression of this OMT cDNA in Escherichia coli further confirmed the identity of the clone. Genomic hybridization demonstrates the presence of one or two OMT genes per haploid poplar genome. RNA gel blot hybridization shows high levels of steady-state OMT mRNA in the xylem of young poplar trees, as compared to the levels in leaves.
The phytopathogen Rhodococcus fascians induces the development of leafy gall, which is considered to be its ecological niche. To obtain a view of the metabolic changes occurring in R. fascians during this process, an in vitro system was...
moreThe phytopathogen Rhodococcus fascians induces the development of leafy gall, which is considered to be its ecological niche. To obtain a view of the metabolic changes occurring in R. fascians during this process, an in vitro system was used where bacteria are grown in the presence of a leafy gall extract, a condition mimicking that found by the bacteria in infected plants. Proteins of R. fascians grown for 24 h under these conditions were displayed by two-dimensional polyacrylamide gel electrophoresis. Fifteen polypeptides showing a differential accumulation in response to the inducing conditions were analyzed by mass spectrometry. Two polypeptides potentially linked to the Krebs cycle, a pyruvate dehydrogenase and a fumarate hydratase, were further characterized and shown to be downregulated at the transcriptional level. The identification of these two enzymes suggests that R. fascians may shift its metabolism during the interaction with plants from the Krebs cycle to the glyoxylate shunt.
Lignin, a complex heteropolymer of cinnamyl alcohols, is, second to cellulose, the most abundant biopolymer on Earth. Lignification has played a determining role in the adaptation of plants to terrestrial life. As all extracellular...
moreLignin, a complex heteropolymer of cinnamyl alcohols, is, second to cellulose, the most abundant biopolymer on Earth. Lignification has played a determining role in the adaptation of plants to terrestrial life. As all extracellular polymers, lignin confers rheological properties to plant ...
... author for correspondence) Received 8 February 2000; accepted 1 September 2000 Key words: forest tree, genetic engineering, lignin, monolignol, poplar, pulp and paper Summary ... Geneticengineering of lignin Downregulation of caffeic...
more... author for correspondence) Received 8 February 2000; accepted 1 September 2000 Key words: forest tree, genetic engineering, lignin, monolignol, poplar, pulp and paper Summary ... Geneticengineering of lignin Downregulation of caffeic acid O-methyltransferase (COMT) ...
DI-fusion, le Dépôt institutionnel numérique de l'ULB, est l'outil de référencementde la production scientifique de l'ULB.L'interface de recherche DI-fusion permet de consulter les publications des chercheurs de...
moreDI-fusion, le Dépôt institutionnel numérique de l'ULB, est l'outil de référencementde la production scientifique de l'ULB.L'interface de recherche DI-fusion permet de consulter les publications des chercheurs de l'ULB et les thèses qui y ont été défendues.