concept of stem cells has been imported from the animal literature with the goal of facilitating ... more concept of stem cells has been imported from the animal literature with the goal of facilitating our understanding and description of plant developmental processes. It is not clear if this is the case, especially in light of the recent experimental results on root regeneration in Arabidopsis mutants .
We used the single-strand conformation polymorphism (SSCP) technique to map six genes on Eucalypt... more We used the single-strand conformation polymorphism (SSCP) technique to map six genes on Eucalyptus urophylla and Eucalyptus grandis linkage maps. These included four genes involved in the common phenylpropanoid pathway (Caffeic acid 3-O-methyltransferase, Caffeoyl CoA 3-O-methyltransferase, 4-Coumarate CoA ligase and phenylalanine ammonia-lyase), two genes involved in the "lignin specific" pathway (Cinnamoyl CoA reductase and Cinnamyl alcohol dehydrogenase). The placement of these genes on the Eucalyptus maps was carried out using an interspecific hybrid mapping population. This will further facilitate the identification or exclusion of "positional" candidate genes for characterizing quantitative trait loci (QTL) for traits related to wood quality. We have studied colocations between these candidate genes and QTL for longitudinal growth strain and wood density. The 4-coumarate CoA gene seems to be a good candidate for wood density as measured by pilodyn. (Texte ...
L'eucalyptus, premiere espece de reboisement au monde, est largement utilise en industrie pap... more L'eucalyptus, premiere espece de reboisement au monde, est largement utilise en industrie papetiere. Toutefois, les lignines qui representent un quart de la biomasse totale du bois constituent un produit indesirable qui limite les rendements en pâte a papier. L'extraction de ces composes phenoliques est realisee par des processus chimiques onereux et tres polluants. Il apparait donc souhaitable, d'un point de vue economique et environnemental, de developper des varietes d'eucalyptus, presentant une reduction de teneurs en lignines et/ou des lignines plus facilement extractibles. Une strategie envisageable est d'exploiter la variabilite genetique qui controle l'heterogeneite naturelle des lignines dans des programmes de selection genetique. Dans cet objectif, on peut envisager d'utiliser des marqueurs moleculaires de fonction connue a priori directement impliques dans le controle genetique de la quantite et/ou de la qualite des lignines. Les enzymes impliq...
To understand how the identity of an organ can be switched, we studied the transformation of late... more To understand how the identity of an organ can be switched, we studied the transformation of lateral root primordia (LRP) into shoot meristems in Arabidopsis root segments. In this system, the cytokinin-induced conversion does not involve the formation of callus-like structures. Detailed analysis showed that the conversion sequence starts with a mitotic pause and is concomitant with the differential expression of regulators of root and shoot development. The conversion requires the presence of apical stem cells and only LRP at stages VI or VII can be switched. It is engaged as soon as cell divisions resume because their position and orientation differ in the converting organ compared to the undisturbed emerging LRP. By alternating auxin and cytokinin treatments, we showed that the root and shoot organogenetic programs are remarkably plastic because the status of the same plant stem cell niche can be reversed repeatedly within a set developmental window. Thus, the networks at play in...
Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) catalyses the last step in the synthesis of th... more Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) catalyses the last step in the synthesis of the monomeric precursors of lignin. Here, we demonstrate that the vascular expression pattern conferred by the Eucalyptus gunniiEgCAD2 promoter in transgenic poplar (Populus tremula × Populus alba) is conserved in another perennial woody angiosperm of economic interest (Vitis vinifera L.), as well as in a model
EgMYB2, a member of a new subgroup of the R2R3 MYB family of transcription factors, was cloned fr... more EgMYB2, a member of a new subgroup of the R2R3 MYB family of transcription factors, was cloned from a library consisting of RNA from differentiating Eucalyptus xylem. EgMYB2 maps to a unique locus on the Eucalyptus grandis linkage map and co-localizes with a quantitative trait locus (QTL) for lignin content. Recombinant EgMYB2 protein was able to bind specifically the cis-regulatory regions of the promoters of two lignin biosynthetic genes, cinnamoyl-coenzyme A reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD), which contain MYB consensus binding sites. EgMYB2 was also able to regulate their transcription in both transient and stable expression assays. Transgenic tobacco plants over-expressing EgMYB2 displayed phenotypic changes relative to wild-type plants, among which were a dramatic increase in secondary cell wall thickness, and an alteration of the lignin profiles. Transcript abundance of genes encoding enzymes specific to lignin biosynthesis was increased to varying extents according to the position of individual genes in the pathway, whereas core phenylpropanoid genes were not significantly affected. Together these results suggest a role for EgMYB2 in the coordinated control of genes belonging to the monolignol-specific pathway, and therefore in the biosynthesis of lignin and the regulation of secondary cell wall formation.
We have previously shown that the Eucalyptus gunnii EgCAD2 promoter was preferentially expressed ... more We have previously shown that the Eucalyptus gunnii EgCAD2 promoter was preferentially expressed in vascular tissues in different transgenic plants (poplar, tobacco, Arabidopsis and grapevine). In order to delineate the cis elements governing this vascular expression pattern, promoter deletion analysis was performed allowing us to identify the proximal region [À340/À124] as essential for vascular cambium/ xylem-specific expression. In plants transformed with the smallest promoter region [À124/þ117], the GUS activity was difficult to detect using conventional bright field microscopy. To overcome this problem, we used fluorescence microscopy, enabling us to show that the [À124/þ117] region contained cis-elements driving activity in phloem fibres but not in secondary xylem. The technical improvement of the histochemical detection of GUS activity using fluorescence microscopy enables accurate investigation of low GUS activity in phenol-rich tissues.
Background Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) catalyze the fi... more Background Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) catalyze the final steps in the biosynthesis of monolignols, the monomeric units of the phenolic lignin polymers which confer rigidity, imperviousness and resistance to biodegradation to cell walls. We have previously shown that the Eucalyptus gunnii CCR and CAD2 promoters direct similar expression patterns in vascular tissues suggesting that monolignol production is controlled, at least in part, by the coordinated transcriptional regulation of these two genes. Although consensus motifs for MYB transcription factors occur in most gene promoters of the whole phenylpropanoid pathway, functional evidence for their contribution to promoter activity has only been demonstrated for a few of them. Here, in the lignin-specific branch, we studied the functional role of MYB elements as well as other cis-elements identified in the regulatory regions of EgCAD2 and EgCCR promoters, in the transcriptional activity of...
Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) catalyses the last step in the synthesis of th... more Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) catalyses the last step in the synthesis of the monomeric precursors of lignin. Here, we demonstrate that the vascular expression pattern conferred by the Eucalyptus gunnii EgCAD2 promoter in transgenic poplar (Populus tremula x Populus alba) is conserved in another perennial woody angiosperm of economic interest (Vitis vinifera L.), as well as in a model herbaceous plant (Nicotiana tabacum L.). Furthermore, promoter deletion analysis performed in both tobacco and poplar allowed us to identify the proximal region [-340/-124] as essential for vascular cambium/xylem-specific expression whereas the [-124/+117] region was shown to contain cis element-driving activity in phloem fibres. Interestingly, the [-340/-124] fragment contains an AC-rich cis-acting element present in numerous genes of the phenylpropanoid pathway expressed in xylem tissues, and known as a consensus Myb transcription factor binding site, suggesting that common Myb s...
EgMYB2, a member of a new subgroup of the R2R3 MYB family of transcription factors, was cloned fr... more EgMYB2, a member of a new subgroup of the R2R3 MYB family of transcription factors, was cloned from a library consisting of RNA from differentiating Eucalyptus xylem. EgMYB2 maps to a unique locus on the Eucalyptus grandis linkage map and co-localizes with a quantitative trait locus (QTL) for lignin content. Recombinant EgMYB2 protein was able to bind specifically the cis-regulatory regions of the promoters of two lignin biosynthetic genes, cinnamoyl-coenzyme A reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD), which contain MYB consensus binding sites. EgMYB2 was also able to regulate their transcription in both transient and stable expression assays. Transgenic tobacco plants over-expressing EgMYB2 displayed phenotypic changes relative to wild-type plants, among which were a dramatic increase in secondary cell wall thickness, and an alteration of the lignin profiles. Transcript abundance of genes encoding enzymes specific to lignin biosynthesis was increased to varying extents according to the position of individual genes in the pathway, whereas core phenylpropanoid genes were not significantly affected. Together these results suggest a role for EgMYB2 in the co-ordinated control of genes belonging to the monolignol-specific pathway, and therefore in the biosynthesis of lignin and the regulation of secondary cell wall formation.
We have previously shown that the Eucalyptus gunnii EgCAD2 promoter was preferentially expressed ... more We have previously shown that the Eucalyptus gunnii EgCAD2 promoter was preferentially expressed in vascular tissues in different transgenic plants (poplar, tobacco, Arabidopsis and grapevine). In order to delineate the cis elements governing this vascular expression pattern, promoter deletion analysis was performed allowing us to identify the proximal region [À340/À124] as essential for vascular cambium/ xylem-specific expression. In plants transformed with the smallest promoter region [À124/þ117], the GUS activity was difficult to detect using conventional bright field microscopy. To overcome this problem, we used fluorescence microscopy, enabling us to show that the [À124/þ117] region contained cis-elements driving activity in phloem fibres but not in secondary xylem. The technical improvement of the histochemical detection of GUS activity using fluorescence microscopy enables accurate investigation of low GUS activity in phenol-rich tissues.
We have established a detailed framework for the process of shoot regeneration from Arabidopsis r... more We have established a detailed framework for the process of shoot regeneration from Arabidopsis root and hypocotyl explants grown in vitro. Using transgenic plant lines in which the GUS or GFP genes were fused to promoters of developmental genes (WUS, CLV1, CLV3, STM, CUC1, PLT1, RCH1, QC25), or to promoters of genes encoding indicators of the auxin response (DR5) or transport (PIN1), cytokinin (CK) response (ARR5) or synthesis (IPT5), or mitotic activity (CYCB1), we showed that regenerated shoots originated directly or indirectly from the pericycle cells adjacent to xylem poles. In addition, shoot regeneration appeared to be partly similar to the formation of lateral root meristems (LRMs). During pre-culture on a 2, 4-dichlorophenoxyacetic acid (2, 4-D)-rich callus-inducing medium (CIM), xylem pericycle reactivation established outgrowths that were not true calli but had many characteristics of LRMs. Transfer to a CK-rich shoot-inducing medium (SIM) resulted in early LRM-like primordia changing to shoot meristems. Direct origin of shoots from the xylem pericycle occurred upon direct culture on CK-containing media without prior growth on CIM. Thus, it appeared that the xylem pericycle is more pluripotent than previously thought. This pluripotency was accompanied by the ability of pericycle derivatives to retain diploidy, even after several rounds of cell division. In contrast, the phloem pericycle did not display such developmental plasticity, and responded to CKs with only periclinal divisions. Such observations reinforce the view that the pericycle is an 'extended meristem' that comprises two types of cell populations. They also suggest that the founder cells for LRM initiation are not initially fully specified for this developmental pathway.
Growth and genetic stability of Nicotiana tabacum L. callus were strongly improved by replacing t... more Growth and genetic stability of Nicotiana tabacum L. callus were strongly improved by replacing the inorganic nitrogen and phosphorus of the Murashige and Skoog's medium by a soybean peptone and phytate, respectively. Cell proliferation after subcultivation on the modified medium was highly stimulated as evidenced by a strong biomass increase; this improvement was mainly due to the organic N source. In addition, while calluses grown under standard conditions displayed various cell sizes and DNA contents, subcultivation on the modified medium led to homogeneous cell size distribution and stable 4C-8C DNA contents through several subcultures. This improved genetic stability was due to replacement of inorganic P by phytate, provided the presence of peptone. Such new media composition could be useful for slow-growing cell suspensions or calluses.
Background: Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) catalyze the f... more Background: Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) catalyze the final steps in the biosynthesis of monolignols, the monomeric units of the phenolic lignin polymers which confer rigidity, imperviousness and resistance to biodegradation to cell walls. We have previously shown that the Eucalyptus gunnii CCR and CAD2 promoters direct similar expression patterns in vascular tissues suggesting that monolignol production is controlled, at least in part, by the coordinated transcriptional regulation of these two genes. Although consensus motifs for MYB transcription factors occur in most gene promoters of the whole phenylpropanoid pathway, functional evidence for their contribution to promoter activity has only been demonstrated for a few of them. Here, in the ligninspecific branch, we studied the functional role of MYB elements as well as other cis-elements identified in the regulatory regions of EgCAD2 and EgCCR promoters, in the transcriptional activity of these gene promoters.
We used the single-strand conformation polymorphism (SSCP) technique to map eight genes on Eucaly... more We used the single-strand conformation polymorphism (SSCP) technique to map eight genes on Eucalyptus urophylla and Eucalyptus grandis linkage maps. These included four genes involved in the common phenylpropanoid pathway (caffeic acid 3-0-methyltransferase, caffeoyl CoA 3-O-methyltransferase, 4-coumarate CoA ligase and phenylalanine ammonia-lyase), two genes involved in the 'lignin specific' pathway (cinnamoyl CoA reductase and cinnamyl alcohol dehydrogenase), and two symbiosis regulated genes (EgHypar and EgTubA1). A novel source of variation which affects the SSCP pattern, i.e. the presence or absence of electrophoresis buffer upon loading the samples into the polyacrylamide gel, was found. The placement of these genes on the Eucalyptus maps was carried out using an interspecific hybrid mapping population. This will further facilitate the identification or exclusion of 'positional' candidate genes for characterizing quantitative trait loci (QTL) for wood quality and vegetative propagation related traits.
concept of stem cells has been imported from the animal literature with the goal of facilitating ... more concept of stem cells has been imported from the animal literature with the goal of facilitating our understanding and description of plant developmental processes. It is not clear if this is the case, especially in light of the recent experimental results on root regeneration in Arabidopsis mutants .
We used the single-strand conformation polymorphism (SSCP) technique to map six genes on Eucalypt... more We used the single-strand conformation polymorphism (SSCP) technique to map six genes on Eucalyptus urophylla and Eucalyptus grandis linkage maps. These included four genes involved in the common phenylpropanoid pathway (Caffeic acid 3-O-methyltransferase, Caffeoyl CoA 3-O-methyltransferase, 4-Coumarate CoA ligase and phenylalanine ammonia-lyase), two genes involved in the "lignin specific" pathway (Cinnamoyl CoA reductase and Cinnamyl alcohol dehydrogenase). The placement of these genes on the Eucalyptus maps was carried out using an interspecific hybrid mapping population. This will further facilitate the identification or exclusion of "positional" candidate genes for characterizing quantitative trait loci (QTL) for traits related to wood quality. We have studied colocations between these candidate genes and QTL for longitudinal growth strain and wood density. The 4-coumarate CoA gene seems to be a good candidate for wood density as measured by pilodyn. (Texte ...
L'eucalyptus, premiere espece de reboisement au monde, est largement utilise en industrie pap... more L'eucalyptus, premiere espece de reboisement au monde, est largement utilise en industrie papetiere. Toutefois, les lignines qui representent un quart de la biomasse totale du bois constituent un produit indesirable qui limite les rendements en pâte a papier. L'extraction de ces composes phenoliques est realisee par des processus chimiques onereux et tres polluants. Il apparait donc souhaitable, d'un point de vue economique et environnemental, de developper des varietes d'eucalyptus, presentant une reduction de teneurs en lignines et/ou des lignines plus facilement extractibles. Une strategie envisageable est d'exploiter la variabilite genetique qui controle l'heterogeneite naturelle des lignines dans des programmes de selection genetique. Dans cet objectif, on peut envisager d'utiliser des marqueurs moleculaires de fonction connue a priori directement impliques dans le controle genetique de la quantite et/ou de la qualite des lignines. Les enzymes impliq...
To understand how the identity of an organ can be switched, we studied the transformation of late... more To understand how the identity of an organ can be switched, we studied the transformation of lateral root primordia (LRP) into shoot meristems in Arabidopsis root segments. In this system, the cytokinin-induced conversion does not involve the formation of callus-like structures. Detailed analysis showed that the conversion sequence starts with a mitotic pause and is concomitant with the differential expression of regulators of root and shoot development. The conversion requires the presence of apical stem cells and only LRP at stages VI or VII can be switched. It is engaged as soon as cell divisions resume because their position and orientation differ in the converting organ compared to the undisturbed emerging LRP. By alternating auxin and cytokinin treatments, we showed that the root and shoot organogenetic programs are remarkably plastic because the status of the same plant stem cell niche can be reversed repeatedly within a set developmental window. Thus, the networks at play in...
Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) catalyses the last step in the synthesis of th... more Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) catalyses the last step in the synthesis of the monomeric precursors of lignin. Here, we demonstrate that the vascular expression pattern conferred by the Eucalyptus gunniiEgCAD2 promoter in transgenic poplar (Populus tremula × Populus alba) is conserved in another perennial woody angiosperm of economic interest (Vitis vinifera L.), as well as in a model
EgMYB2, a member of a new subgroup of the R2R3 MYB family of transcription factors, was cloned fr... more EgMYB2, a member of a new subgroup of the R2R3 MYB family of transcription factors, was cloned from a library consisting of RNA from differentiating Eucalyptus xylem. EgMYB2 maps to a unique locus on the Eucalyptus grandis linkage map and co-localizes with a quantitative trait locus (QTL) for lignin content. Recombinant EgMYB2 protein was able to bind specifically the cis-regulatory regions of the promoters of two lignin biosynthetic genes, cinnamoyl-coenzyme A reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD), which contain MYB consensus binding sites. EgMYB2 was also able to regulate their transcription in both transient and stable expression assays. Transgenic tobacco plants over-expressing EgMYB2 displayed phenotypic changes relative to wild-type plants, among which were a dramatic increase in secondary cell wall thickness, and an alteration of the lignin profiles. Transcript abundance of genes encoding enzymes specific to lignin biosynthesis was increased to varying extents according to the position of individual genes in the pathway, whereas core phenylpropanoid genes were not significantly affected. Together these results suggest a role for EgMYB2 in the coordinated control of genes belonging to the monolignol-specific pathway, and therefore in the biosynthesis of lignin and the regulation of secondary cell wall formation.
We have previously shown that the Eucalyptus gunnii EgCAD2 promoter was preferentially expressed ... more We have previously shown that the Eucalyptus gunnii EgCAD2 promoter was preferentially expressed in vascular tissues in different transgenic plants (poplar, tobacco, Arabidopsis and grapevine). In order to delineate the cis elements governing this vascular expression pattern, promoter deletion analysis was performed allowing us to identify the proximal region [À340/À124] as essential for vascular cambium/ xylem-specific expression. In plants transformed with the smallest promoter region [À124/þ117], the GUS activity was difficult to detect using conventional bright field microscopy. To overcome this problem, we used fluorescence microscopy, enabling us to show that the [À124/þ117] region contained cis-elements driving activity in phloem fibres but not in secondary xylem. The technical improvement of the histochemical detection of GUS activity using fluorescence microscopy enables accurate investigation of low GUS activity in phenol-rich tissues.
Background Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) catalyze the fi... more Background Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) catalyze the final steps in the biosynthesis of monolignols, the monomeric units of the phenolic lignin polymers which confer rigidity, imperviousness and resistance to biodegradation to cell walls. We have previously shown that the Eucalyptus gunnii CCR and CAD2 promoters direct similar expression patterns in vascular tissues suggesting that monolignol production is controlled, at least in part, by the coordinated transcriptional regulation of these two genes. Although consensus motifs for MYB transcription factors occur in most gene promoters of the whole phenylpropanoid pathway, functional evidence for their contribution to promoter activity has only been demonstrated for a few of them. Here, in the lignin-specific branch, we studied the functional role of MYB elements as well as other cis-elements identified in the regulatory regions of EgCAD2 and EgCCR promoters, in the transcriptional activity of...
Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) catalyses the last step in the synthesis of th... more Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) catalyses the last step in the synthesis of the monomeric precursors of lignin. Here, we demonstrate that the vascular expression pattern conferred by the Eucalyptus gunnii EgCAD2 promoter in transgenic poplar (Populus tremula x Populus alba) is conserved in another perennial woody angiosperm of economic interest (Vitis vinifera L.), as well as in a model herbaceous plant (Nicotiana tabacum L.). Furthermore, promoter deletion analysis performed in both tobacco and poplar allowed us to identify the proximal region [-340/-124] as essential for vascular cambium/xylem-specific expression whereas the [-124/+117] region was shown to contain cis element-driving activity in phloem fibres. Interestingly, the [-340/-124] fragment contains an AC-rich cis-acting element present in numerous genes of the phenylpropanoid pathway expressed in xylem tissues, and known as a consensus Myb transcription factor binding site, suggesting that common Myb s...
EgMYB2, a member of a new subgroup of the R2R3 MYB family of transcription factors, was cloned fr... more EgMYB2, a member of a new subgroup of the R2R3 MYB family of transcription factors, was cloned from a library consisting of RNA from differentiating Eucalyptus xylem. EgMYB2 maps to a unique locus on the Eucalyptus grandis linkage map and co-localizes with a quantitative trait locus (QTL) for lignin content. Recombinant EgMYB2 protein was able to bind specifically the cis-regulatory regions of the promoters of two lignin biosynthetic genes, cinnamoyl-coenzyme A reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD), which contain MYB consensus binding sites. EgMYB2 was also able to regulate their transcription in both transient and stable expression assays. Transgenic tobacco plants over-expressing EgMYB2 displayed phenotypic changes relative to wild-type plants, among which were a dramatic increase in secondary cell wall thickness, and an alteration of the lignin profiles. Transcript abundance of genes encoding enzymes specific to lignin biosynthesis was increased to varying extents according to the position of individual genes in the pathway, whereas core phenylpropanoid genes were not significantly affected. Together these results suggest a role for EgMYB2 in the co-ordinated control of genes belonging to the monolignol-specific pathway, and therefore in the biosynthesis of lignin and the regulation of secondary cell wall formation.
We have previously shown that the Eucalyptus gunnii EgCAD2 promoter was preferentially expressed ... more We have previously shown that the Eucalyptus gunnii EgCAD2 promoter was preferentially expressed in vascular tissues in different transgenic plants (poplar, tobacco, Arabidopsis and grapevine). In order to delineate the cis elements governing this vascular expression pattern, promoter deletion analysis was performed allowing us to identify the proximal region [À340/À124] as essential for vascular cambium/ xylem-specific expression. In plants transformed with the smallest promoter region [À124/þ117], the GUS activity was difficult to detect using conventional bright field microscopy. To overcome this problem, we used fluorescence microscopy, enabling us to show that the [À124/þ117] region contained cis-elements driving activity in phloem fibres but not in secondary xylem. The technical improvement of the histochemical detection of GUS activity using fluorescence microscopy enables accurate investigation of low GUS activity in phenol-rich tissues.
We have established a detailed framework for the process of shoot regeneration from Arabidopsis r... more We have established a detailed framework for the process of shoot regeneration from Arabidopsis root and hypocotyl explants grown in vitro. Using transgenic plant lines in which the GUS or GFP genes were fused to promoters of developmental genes (WUS, CLV1, CLV3, STM, CUC1, PLT1, RCH1, QC25), or to promoters of genes encoding indicators of the auxin response (DR5) or transport (PIN1), cytokinin (CK) response (ARR5) or synthesis (IPT5), or mitotic activity (CYCB1), we showed that regenerated shoots originated directly or indirectly from the pericycle cells adjacent to xylem poles. In addition, shoot regeneration appeared to be partly similar to the formation of lateral root meristems (LRMs). During pre-culture on a 2, 4-dichlorophenoxyacetic acid (2, 4-D)-rich callus-inducing medium (CIM), xylem pericycle reactivation established outgrowths that were not true calli but had many characteristics of LRMs. Transfer to a CK-rich shoot-inducing medium (SIM) resulted in early LRM-like primordia changing to shoot meristems. Direct origin of shoots from the xylem pericycle occurred upon direct culture on CK-containing media without prior growth on CIM. Thus, it appeared that the xylem pericycle is more pluripotent than previously thought. This pluripotency was accompanied by the ability of pericycle derivatives to retain diploidy, even after several rounds of cell division. In contrast, the phloem pericycle did not display such developmental plasticity, and responded to CKs with only periclinal divisions. Such observations reinforce the view that the pericycle is an 'extended meristem' that comprises two types of cell populations. They also suggest that the founder cells for LRM initiation are not initially fully specified for this developmental pathway.
Growth and genetic stability of Nicotiana tabacum L. callus were strongly improved by replacing t... more Growth and genetic stability of Nicotiana tabacum L. callus were strongly improved by replacing the inorganic nitrogen and phosphorus of the Murashige and Skoog's medium by a soybean peptone and phytate, respectively. Cell proliferation after subcultivation on the modified medium was highly stimulated as evidenced by a strong biomass increase; this improvement was mainly due to the organic N source. In addition, while calluses grown under standard conditions displayed various cell sizes and DNA contents, subcultivation on the modified medium led to homogeneous cell size distribution and stable 4C-8C DNA contents through several subcultures. This improved genetic stability was due to replacement of inorganic P by phytate, provided the presence of peptone. Such new media composition could be useful for slow-growing cell suspensions or calluses.
Background: Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) catalyze the f... more Background: Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) catalyze the final steps in the biosynthesis of monolignols, the monomeric units of the phenolic lignin polymers which confer rigidity, imperviousness and resistance to biodegradation to cell walls. We have previously shown that the Eucalyptus gunnii CCR and CAD2 promoters direct similar expression patterns in vascular tissues suggesting that monolignol production is controlled, at least in part, by the coordinated transcriptional regulation of these two genes. Although consensus motifs for MYB transcription factors occur in most gene promoters of the whole phenylpropanoid pathway, functional evidence for their contribution to promoter activity has only been demonstrated for a few of them. Here, in the ligninspecific branch, we studied the functional role of MYB elements as well as other cis-elements identified in the regulatory regions of EgCAD2 and EgCCR promoters, in the transcriptional activity of these gene promoters.
We used the single-strand conformation polymorphism (SSCP) technique to map eight genes on Eucaly... more We used the single-strand conformation polymorphism (SSCP) technique to map eight genes on Eucalyptus urophylla and Eucalyptus grandis linkage maps. These included four genes involved in the common phenylpropanoid pathway (caffeic acid 3-0-methyltransferase, caffeoyl CoA 3-O-methyltransferase, 4-coumarate CoA ligase and phenylalanine ammonia-lyase), two genes involved in the 'lignin specific' pathway (cinnamoyl CoA reductase and cinnamyl alcohol dehydrogenase), and two symbiosis regulated genes (EgHypar and EgTubA1). A novel source of variation which affects the SSCP pattern, i.e. the presence or absence of electrophoresis buffer upon loading the samples into the polyacrylamide gel, was found. The placement of these genes on the Eucalyptus maps was carried out using an interspecific hybrid mapping population. This will further facilitate the identification or exclusion of 'positional' candidate genes for characterizing quantitative trait loci (QTL) for wood quality and vegetative propagation related traits.
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Papers by Philippe Rech