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PubMed2000

Lignification in transgenic poplars with extremely reduced caffeic acid O-methyltransferase activity.

Transgenic poplars (Populus tremula x Populus alba) were obtained by introduction of a sense homologous transgene encoding caffeic acid O-methyltransferase (COMT) under the control either of the cauliflower mosaic virus double 35S promoter or of the eucalyptus cinnamyl alcohol dehydrogenase promoter. Although these constructs conferred a moderate overexpression of COMT in some lines, a transgenic line with the double 35S promoter was found where COMT activity in woody tissues was close to zero due to a gene-silencing phenomenon. For the first time in COMT down-regulated trees, this alteration substantially reduced lignin level in 6-month-old trees (17% decrease). Lignin structure was found to be strongly altered, with a two times higher content in condensed bonds, an almost complete lack of syringyl units, and the incorporation of 5-hydroxyguaiacyl units to the most remarkable extent reported so far. Consistent with the higher cellulose content and with the higher condensation degree of the lignin, the impact of the transformation on the kraft-pulping performances of the poplar trees positively affected the pulp yield (10% relative increase), but made lignins less amenable to industrial degradations.

Cellulose↗
PubMed2001

Functional characterization and subcellular localization of poplar (Populus trichocarpa x Populus deltoides) cinnamate 4-hydroxylase.

Cinnamic acid 4-hydroxylase (C4H), a member of the cytochrome P450 monooxygenase superfamily, plays a central role in phenylpropanoid metabolism and lignin biosynthesis and possibly anchors a phenylpropanoid enzyme complex to the endoplasmic reticulum (ER). A full-length cDNA encoding C4H was isolated from a hybrid poplar (Populus trichocarpa x P. deltoides) young leaf cDNA library. RNA-blot analysis detected C4H transcripts in all organs tested, but the gene was most highly expressed in developing xylem. C4H expression was also strongly induced by elicitor-treatment in poplar cell cultures. To verify the catalytic activity of the putative C4H cDNA, two constructs, C4H and C4H fused to the FLAG epitope (C4H::FLAG), were expressed in yeast. Immunoblot analysis showed that C4H was present in the microsomal fraction and microsomal preparations from strains expressing both enzymes efficiently converted cinnamic acid to p-coumaric acid with high specific activities. To investigate the subcellular localization of C4H in vivo, a chimeric C4H-green fluorescent protein (GFP) gene was engineered and stably expressed in Arabidopsis. Confocal laser microscopy analysis clearly showed that in Arabidopsis the C4H::GFP chimeric enzyme was localized to the ER. When expressed in yeast, the C4H::GFP fusion enzyme was also active but displayed significantly lower specific activity than either C4H or C4H::FLAG in in vitro and in vivo enzyme assays. These data definitively show that C4H is localized to the ER in planta.

Amino Acid Sequence↗
PubMed2001

Phytochrome-mediated photoperiod perception, shoot growth, glutamine, calcium, and protein phosphorylation influence the activity of the poplar bark storage protein gene promoter (bspA).

In poplars (Populus), bspA encodes a 32-kD bark storage protein that accumulates in the inner bark of plants exposed to either short-day (SD) photoperiods or elevated levels of nitrogen. In this study, poplars transformed with a chimeric gene consisting of the bspA promoter fused to beta-glucuronidase (uidA) were used to investigate the transcriptional regulation of the bspA promoter. Photoperiodic activation of the bspA promoter was shown to involve perception by phytochrome and likely involves both a low fluence response and a parallel very low fluence response pathway. Activity of the bspA promoter was also influenced by shoot growth. High levels of bspA expression usually occur in the bark of plants during SD but not long day or SD with a night break. When growth was inhibited under growth permissive photoperiods (SD with night break) levels of bark beta-glucuronidase (GUS) activity increased. Stimulating shoot growth in plants treated with SD inhibited SD-induced increases in bark GUS activity. Because changes in photoperiod and growth also alter carbon and nitrogen partitioning, the role of carbon and nitrogen metabolites in modulating the activity of the bspA promoter were investigated by treating excised stems with amino acids or NH4NO3 with or without sucrose. Treatment with either glutamine or NH4NO3 resulted in increased stem GUS activity. The addition of sucrose with either glutamine or NH4NO3 resulted in synergistic induction of GUS, whereas sucrose alone had no effect. Glutamine plus sucrose induction of GUS activity was inhibited by EGTA, okadaic acid, or K-252A. Inhibition by EGTA was partially relieved by the addition of Ca2+. The Ca2+ ionophore, ionomycin, also induced GUS activity in excised shoots. These results indicate that transcriptional activation of bspA is complex. It is likely that SD activation of bspA involves perception by phytochrome coupled to changes in growth. These growth changes may then alter carbon and nitrogen partitioning that somehow signals bspA induction by a yet undefined mechanism that involves carbon and nitrogen metabolites, Ca2+, and protein phosphorylation/dephosphorylation.

Calcium↗
PubMed1974

Effect of low temperature on amino Acid metabolism in wintering poplar: arginine-glutamine relationships.

Analyses of free amino acids in poplar (Populus gelrica) were carried out throughout a year to see the effect of low temperature on a system regulating amino acid metabolism in the tree. The results indicated that during the wintering phase arginine was the major amino acid both in bark and xylem, particularly in xylem, and that at the time of budding and growing glutamine and glutamate became dominant. Changes in the relative levels of glutamine (plus glutamate) and arginine to the total amino acids of the alpha-ketoglutarate family indicated the presence of a regulatory system annually controlling the synthesis between glutamine (plus glutamate) and arginine. The system appeared to be governed and sensitized by low temperatures. Neither a transition of the synthesis from arginine to glutamine (plus glutamate) nor budding occurred in the poplars which spent the winter months in a greenhouse.

Journal Article↗
PubMed1992

A cold environment is a prerequisite for formation of "plastid initials" in winter buds of poplar.

The "plastid initial," the presumed precursor of eoplasts and proplastids, is present in the cells of the apical meristem of winter buds of poplar (Populus euramericana). The formation of the plastid initial in the cells of winter buds is initiated soon after the breaking of the innate or resting stage of dormancy, even in winter under nongrowing conditions in mid-January or early February. From this stage to March, the conglomeration of the plastid initial and the formation of prolamellar bodies is evident. In contrast to the poplar samples kept outdoors, the cells of the apical meristem of the indoor winter buds did not show any indication of the formation of the plastid initial and the buds of the latter sample did not flush even at the end of May. These results suggest that the sequence of reactions involved in the onset of regrowth may be closely related to the formation of the plastid initial.

Journal Article↗
PubMed2002

PtABI3 impinges on the growth and differentiation of embryonic leaves during bud set in poplar.

The Arabidopsis ABSCISIC ACID-INSENSITIVE3 (ABI3) protein plays a crucial role during late seed development and has an additional function at the vegetative meristem, particularly during periods of growth-arresting conditions and quiescence. Here, we show that the ABI3 homolog of poplar (PtABI3) is expressed in buds during natural bud set. Expression occurs clearly after perception of the critical daylength that initiates bud set and dormancy in poplar. In short-day conditions mimicking natural bud set, the expression of a chimeric PtABI3::beta-glucuronidase (GUS) gene occurred in those organs and cells of the apex that grow actively but will undergo arrest: the young embryonic leaves, the subapical meristem, and the procambial strands. If PtABI3 is overexpressed or downregulated, bud development in short-day conditions is altered. Constitutive overexpression of PtABI3 resulted in apical buds with large embryonic leaves and small stipules, whereas in antisense lines, bud scales were large and leaves were small. Thus, PtABI3 influences the size and ratio of embryonic leaves and bud scales/stipules that differentiate from the primordia under short-day conditions. These observations, together with the expression of PtABI3::GUS in embryonic leaves but not in bud scales/stipules, support the idea that wild-type PtABI3 is required for the relative growth rate and differentiation of embryonic leaves inside the bud. These experiments reveal that ABI3 plays a role in the cellular differentiation of vegetative tissues, in addition to its function in seeds.

Abscisic Acid↗
PubMed1994

Accuracy and precision in protein crystal structure analysis: two independent refinements of the structure of poplar plastocyanin at 173 K.

The structure of the copper protein plastocyanin from poplar leaves (Populus nigra var. italica) at 173 K has been subjected to two independent refinements, using a single set of synchrotron X-ray data at 1.6 A resolution. Energy-restrained refinement using the program EREF resulted in lower root-mean-square deviations from ideal geometry (e.g. 0.011 A for bond lengths) but a higher residual R (0.153) than restrained least-squares refinement using the program PROLSQ (0.014 A, 0.132). Electron-density difference maps in both refinements provided evidence for disorder at some side chains and solvent atoms, and the PROLSQ refinement made allowance for this disorder. The number of solvent sites identified at the 4sigma(rho) level was 171 in the EREF refinement and 189 in the PROLSQ refinement; 159 of the solvent sites are common to both refinements within 1 A. The root-mean-square differences between the atomic positions produced by the two refinements are 0.08 A for C(alpha) atoms, 0.08 A for backbone atoms and 0.12 A for all non-H atoms (excluding six obvious outliers) of the protein molecule. The two sets of Cu-ligand bond lengths differ by up to 0.07 A, and the ligand-Cu-ligand angles by up to 7 degrees. At 173 K the volume of the unit cell is 4.2% smaller than at 295 K. Greater order in the solvent region is indicated by the location of 79 more solvent sites, the identification of extensive networks of hydrogen-bonded rings of solvent molecules, and a general decrease in the thermal parameters. Within the unit cell, the protein molecules are significantly translated and rotated from their positions at ambient temperature. An important structural change at low temperature is a 180 degrees flip of the peptide group at Ser48-Gly49. Nearly all other significant differences between the structures of the protein at 173 and 295 K occur at exposed side chains. If the backbone atoms in the 173 and 295 K structures are superposed, excluding atoms involved in the peptide flip, the root-mean- square difference between the positions of 393 atoms is 0.25 A. Two internal water molecules, not included in previous descriptions of poplar plastocyanin, have been located. The plastocyanin Cu-site geometry at 173 K is not significantly different from that at 295 K. If plastocyanin undergoes a change in Cu-site geometry at low temperature, as has been suggested on the basis of resonance Raman spectroscopic evidence, then the change is not detected within the limits of precision of the present results.

Journal Article↗
PubMed1984

Purification and properties of cinnamoyl-CoA reductase and cinnamyl alcohol dehydrogenase from poplar stems (Populus X euramericana).

Cinnamoyl-CoA reductase and cinnamyl alcohol dehydrogenase were purified to apparent homogeneity from poplar stems (Populus euramericana) and their main properties were studied. Only one form was identified for each enzyme. The reductase corresponded to one polypeptide of molecular weight 36 000 and the cinnamyl alcohol dehydrogenase was constituted of two identical subunits of molecular weight 40 000. These characteristics are in agreement with most of the data obtained for the same enzymes isolated from other plants. The two reductive enzymes are inhibited by thiol reagents and a metal chelator 1,10-phenanthroline. The isoelectric point of the reductase (pH 7.5) and of the dehydrogenase (pH 5.6) were determined by chromatofocusing. The cinnamoyl-CoA reductase exhibit a decreasing affinity towards feruloyl-CoA, sinapoyl-CoA and p-coumaroyl-CoA. The cinnamyl alcohol dehydrogenase, which catalyses the reduction of the three cinnamaldehydes, exhibits its highest efficiency towards coniferaldehyde. In spite of differences in the monomeric composition of lignins from xylem and sclerenchyma the reductive enzymes isolated from these two lignified tissues exhibit the same substrate specificity. Consequently, they do not play an important role in the qualitative control of lignins in poplar tissues.

Alcohol Oxidoreductases↗
PubMed2005

Does glutathione metabolism have a role in the defence of poplar against zinc excess?

Transition metals such as zinc (Zn) are essential micronutrients for many physiological processes, but they become toxic at elevated levels. Zinc is one of the most abundant trace heavy metals present in agro-ecosystems. Populus spp. have been suggested as good candidates for using to study the removal and/or immobilization of environmental organic and inorganic pollutants. In order to understand the physiological and biochemical bases of this assumption for Zn, plants of Populus deltoides x P. nigra (P. x euramericana) were grown in hydroponics with different concentrations of Zn [1 microm (control), and 1, 5 and 10 mm] in the nutrient solution.Shoot biomass decreased at 5 and 10 mm Zn, while the Zn content of young leaves increased progressively with increasing Zn concentration (1-10 mm). Total glutathione (GSH+GSSG) content was reduced with increasing Zn concentration, while the contribution of oxidized to total glutathione increased. Despite these observations, semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed that the gene expression of GSH reductase (GR, chloroplastic and cytosolic isoform) and gamma-glutamylcysteine synthetase (gamma-ECS) increased in young leaves of poplars treated with excess Zn. We conclude that GSH synthesis, consumption and redox status play a central role in the response of poplars to high concentrations of Zn.

Crosses, Genetic↗
PubMed2005

Differences in the kinetics and scale of signalling molecule production modulate the ozone sensitivity of hybrid poplar clones: the roles of H2O2, ethylene and salicylic acid.

Hydrogen peroxide (H(2)O(2)), ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC) and salicylic acid (SA) concentrations and ACC synthase (ACS) gene expression were measured to establish whether the high sensitivity of the Populus deltoides x maximowiczii clone Eridano to ozone (O(3)) exposure, compared with the O(3)-resistant Populus deltoides x euramericana clone I-214, is attributable to differences in the modulation of signal transduction pathways. In a time-course experiment, Populus deltoides (poplar) clones were exposed to acute fumigation with 150 nl l(-1) O(3) for 5 h. The two poplar clones showed differences in ethylene evolution, I-214 displaying earlier and less pronounced ethylene emission than Eridano. In both clones, ethylene evolution was accompanied by increased ACS transcript levels and enhanced emission of free ACC. I-214 exhibited a greater basal concentration of free SA and a lower concentration of the conjugated pool. However, a slight accumulation of free SA at the end of the 5-h exposure was found only in Eridano, together with an earlier minimal increase in the concentration of conjugated SA. The results show that both clones react to O(3) by producing H(2)O(2), ethylene and SA, but the difference in sensitivity to the pollutant is probably attributable to differences in the kinetics and magnitude of this response.

Base Sequence↗
PubMed2005

The high-affinity poplar ammonium importer PttAMT1.2 and its role in ectomycorrhizal symbiosis.

One way to elucidate whether ammonium could act as a nitrogen (N) source delivered by the fungus in ectomycorrhizal symbiosis is to investigate plant ammonium importers. Expression analysis of a high-affinity ammonium importer from Populus tremulax tremuloides (PttAMT1.2) and of known members of the AMT1 gene family from Populus trichocarpa was performed. In addition, PttAMT1.2 function was studied in detail by heterologous expression in yeast. PttAMT1.2 expression proved to be root-specific, affected by N nutrition, and strongly increased in a N-independent manner upon ectomycorrhiza formation. The corresponding protein had a K(M) value for ammonium of c. 52 microm. From the seven members of the AMT1 gene family, one gene was exclusively expressed in roots while four genes were detectable in all poplar organs but with varying degrees of expression. Ectomycorrhiza formation resulted in a strong upregulation of three of these genes. Our results indicate an increased ammonium uptake capacity of mycorrhized poplar roots and suggest, together with the expression of putative ammonium exporter genes in the ectomycorrhizal fungus Amanita muscaria, that ammonium could be a major N source delivered from the fungus towards the plant in symbiosis.

Base Sequence↗
PubMed1992

Propolis allergy (IV). Studies with further sensitizers from propolis and constituents common to propolis, poplar buds and balsam of Peru.

26 different compounds have been investigated experimentally for their sensitizing capacity in guinea pigs. 19 of these occur in propolis as well as in poplar bud exudates, and 14 of them are also found in balsam of Peru. 4 caffeates and benzyl isoferulate were found to be strong sensitizers. 7 compounds were moderate, and 13 compounds showed only weak sensitizing potency. Methyl cinnamate was negative. Patch tests in 11 propolis-sensitive patients once more revealed 3-methyl-2-butenyl caffeate and phenylethyl caffeate as the major sensitizers. In addition to the 8 compounds already known to occur in propolis as well as in balsam of Peru, we detected 5 further substances that both materials have in common. Among these, benzyl isoferulate is considered a noteworthy sensitizer. Coniferyl benzoate, which was shown to be a moderate sensitizer, is present in fresh samples of balsam of Peru, while in propolis it has been detected only once so far. The flavonoid aglycones occurring in poplar bud exudates, and hence also in propolis, are weak sensitizers which play only a minor role in propolis hypersensitivity.

Allergens↗
PubMed2025

Tonoplast sucrose transporter SUT4-dependent sugar partitioning modulates phenological transitions and reproductive success in poplar.

Climate uncertainty is intensifying the need for greater plasticity in carbohydrate reserve utilization to support winter survival and spring growth in woody perennials. In poplar, the single-copy SUT4, which encodes a tonoplast-localized sucrose transporter, and the SUT5/SUT6 genome duplicates, which encode plasma membrane-localized transporters, are expressed year-round, with SUT4 showing the highest expression during cool seasons. Given its role in vacuolar sucrose efflux and winter-predominant expression, SUT4 may play a key role in modulating seasonal carbohydrate dynamics. While SUT4-knockdown and knockout effects have been studied under greenhouse conditions, their impact under field conditions remains unexplored. Here, we report a field-based study comparing CRISPR knockout mutants of winter-expressed SUT4 and SUT5/SUT6 in Populus tremula × alba. We show that sut4, but not sut5/6, mutants exhibited earlier autumn leaf senescence, delayed spring bud flush, reduced stem growth, and altered sugar partitioning in winter xylem and bark relative to controls. After 2 years in the field, all genotypes flowered before leaf flush in early spring; however, sut4 mutants produced sterile ovules despite developing normal-looking catkins. Metabolic profiling revealed disrupted sucrose and raffinose dynamics in elongating sut4 catkins. This was accompanied by transcriptomic signatures of elevated stress and downregulation of proanthocyanidin biosynthesis and circadian clock genes. These findings highlight the critical role of SUT4 in coordinating sugar allocation, stress responses, and seasonal development in poplar.

Populus↗
PubMed1981

Poplar lignin decomposition by gram-negative aerobic bacteria.

Eleven gram-negative aerobic bacteria (Pseudomonadaceae and Neisseriaceae) out of 122 soil isolates were selected for their ability to assimilate poplar dioxane lignin without a cosubstrate. Dioxane lignin and milled wood lignin degradation rates ranged between 20 and 40% of initial content after 7 days in mineral medium, as determined by a loss of absorbance at 280 nm; 10 strains could degrade in situ lignin, as evidenced by the decrease of the acetyl bromide lignin content of microtome wood sections. No degradation of wood polysaccharides was detected. Lignin biodegradation by Pseudomonas 106 was confirmed by CO(2) release from labeled poplar wood, although in lower yields compared with results obtained through chemical analysis based on acetyl bromide residual lignin determination.

Journal Article↗
PubMed2005

Horizontal gene transfer to endogenous endophytic bacteria from poplar improves phytoremediation of toluene.

Poplar, a plant species frequently used for phytoremediation of groundwater contaminated with organic solvents, was inoculated with the endophyte Burkholderia cepacia VM1468. This strain, whose natural host is yellow lupine, contains the pTOM-Bu61 plasmid coding for constitutively expressed toluene degradation. Noninoculated plants or plants inoculated with the soil bacterium B. cepacia Bu61(pTOM-Bu61) were used as controls. Inoculation of poplar had a positive effect on plant growth in the presence of toluene and reduced the amount of toluene released via evapotranspiration. These effects were more dramatic for VM1468, the endophytic strain, than for Bu61. Remarkably, none of the strains became established at detectable levels in the endophytic community, but there was horizontal gene transfer of pTOM-Bu61 to different members of the endogenous endophytic community, both in the presence and in the absence of toluene. This work is the first report of in planta horizontal gene transfer among plant-associated endophytic bacteria and demonstrates that such transfer could be used to change natural endophytic microbial communities in order to improve the remediation of environmental insults.

Biodegradation, Environmental↗
PubMed1983

Investigation of white-rot fungi for the conversion of poplar into a potential feedstuff for ruminants.

Five isolates of wood-rotting fungi were compared for their ability to increase the digestibility of poplar shavings. Homogenates of the fungi were inoculated into mixtures of 25 g of shavings and 100 mL of supplementary nutrient solution and incubated at 25 degrees C. The in vitro rumen digestibility of the products increased from 30% at the start of the fermentation to maxima of 72% with Polyporus anceps after 8 weeks, 64% with Ganoderma applanatum and 62% with Phanerochaete chrysosporium after 4 weeks, 61% with Polyporus versicolor after 3 weeks, and 42% with Fomitopsis ulmarius after 4 weeks. Fibre analysis showed a decrease in lignin as digestibility increased. Loss of carbohydrates occurred in all fermentations and continued after lignin loss ceased. Dry matter yield at the time of maximum digestibility ranged from 80 to 94% of the original dry matter. The highest digestibilities attained were similar to those of conventional roughage feeds for ruminants. This shows that this fermentation could form the basis of a practical system for converting poplar into a feedstuff.

Animal Feed↗
PubMed1994

Compositional analysis of the oligosaccharide units of xyloglucans from suspension-cultured poplar cells.

Xyloglucan which was isolated from the walls of suspension-cultured poplar cells showed an average mol wt of 45,000; the extracellular xyloglucan is 25,000 mol wt. Compositional analysis of the oligosaccharide units with Streptomyces endo-1,4-beta-glucanase indicated that the polysaccharides were mainly constructed of four kinds of oligosaccharide repeating units, XLFG, XXFG, XXLG, and XXXG. Poplar xyloglucans contain these four units distributed at random, but primarily at the same ratio among their molecules.

Carbohydrate Sequence↗
PubMed2006

Poplar (Populus spp.).

Although species within the genus Populus are, in general, easier to transform and regenerate in vitro than most other trees, many poplar species are very recalcitrant. Many protocols that previously have been reported were developed for a specific genotype or species. Thus, it has often been necessary to re-optimize a protocol each time research is initiated with a new genotype. The method presented in this chapter has been effective for a wide variety of poplar genotypes.

Agrobacterium tumefaciens↗