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PubMed2006

Genome-wide analysis of the structural genes regulating defense phenylpropanoid metabolism in Populus.

Salicin-based phenolic glycosides, hydroxycinnamate derivatives and flavonoid-derived condensed tannins comprise up to one-third of Populus leaf dry mass. Genes regulating the abundance and chemical diversity of these substances have not been comprehensively analysed in tree species exhibiting this metabolically demanding level of phenolic metabolism. Here, shikimate-phenylpropanoid pathway genes thought to give rise to these phenolic products were annotated from the Populus genome, their expression assessed by semiquantitative or quantitative reverse transcription polymerase chain reaction (PCR), and metabolic evidence for function presented. Unlike Arabidopsis, Populus leaves accumulate an array of hydroxycinnamoyl-quinate esters, which is consistent with broadened function of the expanded hydroxycinnamoyl-CoA transferase gene family. Greater flavonoid pathway diversity is also represented, and flavonoid gene families are larger. Consistent with expanded pathway function, most of these genes were upregulated during wound-stimulated condensed tannin synthesis in leaves. The suite of Populus genes regulating phenylpropanoid product accumulation should have important application in managing phenolic carbon pools in relation to climate change and global carbon cycling.

Coumaric Acids↗

PubMed2002

Microsatellite DNA fingerprinting, differentiation, and genetic relationships of clones, cultivars, and varieties of six poplar species from three sections of the genus Populus.

Accurate identification of Populus clones and cultivars is essential for effective selection, breeding, and genetic resource management programs. The unit of cultivation and breeding in poplars is a clone, and individual cultivars are normally represented by a single clone. Microsatellite DNA markers of 10 simple sequence repeat loci were used for genetic fingerprinting and differentiation of 96 clones/cultivars and varieties belonging to six Populus species (P. deltoides, P. nigra, P. balsamifera, P. trichocarpa, P. grandidentata, and P maximowiczii) from three sections of the genus. All 96 clones/cultivars could be uniquely fingerprinted based on their single- or multilocus microsatellite genotypes. The five P. grandidentata clones could be differentiated based on their single-locus genotypes, while six clones of P. trichocarpa and 11 clones of P. maximowiczii could be identified by their two-locus genotypes. Twenty clones of P. deltoides and 25 clones of P. nigra could be differentiated by their multilocus genotypes employing three loci, and 29 clones of P. balsamifera required the use of multilocus genotypes at five loci for their genetic fingerprinting and differentiation. The loci PTR3, PTR5, and PTR7 were found to be the most informative for genetic fingerprinting and differentiation of the clones. The mean number of alleles per locus ranged from 2.9 in P. trichocarpa or P. grandidentata to 6.0 in P. balsamifera and 11.2 in 96 clones of the six species. The mean number of observed genotypes per locus ranged from 2.4 in P. grandidentata to 7.4 in P. balsamifera and 19.6 in 96 clones of the six species. The mean number of unique genotypes per locus ranged from 1.3 in P. grandidentata to 3.9 in P. deltoides and 8.8 in 96 clones of the six species. The power of discrimination of the microsatellite DNA markers in the 96 clones ranged from 0.726 for PTR4 to 0.939 for PTR7, with a mean of 0.832 over the 10 simple sequence repeat loci. Clones/cultivars from the same species showed higher microsatellite DNA similarities than the clones from the different species. A UPGMA cluster plot constructed from the microsatellite genotypic similarities separated the 96 clones into six major groups corresponding to their species. Populus nigra var. italica clones were genetically differentiated from the P. nigra var. nigra clones. Microsatellite DNA markers could be useful in genetic fingerprinting, identification, classification, certification, and registration of clones, clultivars, and varieties as well as genetic resource management and protection of plant breeders' rights in Populus.

DNA Fingerprinting↗

PubMed2002

[Change of moisture retention in sandy soil after planting mixed forest of Populus spp. and Robinia pseudoacacia].

The change of soil moisture retention after planting mixed forest of Populus spp. and Robinia pseudoacacia was studied by comparative method. The results showed that soil moisture retention, spatial distribution of soil pore, and soil water capacity were improved and increased in sandy soil after Populus spp. and Robinia pseudoacacia being planted, and the improvement in the mixed forest of Populus spp. and R. pseudoacacia was greater than that in the pure forest of Populus spp. or R. pseudoacacia. The basic reason of soil moisture retention being improved was the increment of soil organic matter, which improved soil pore condition.

Ecosystem↗

PubMed2000

Diverse effects of overexpression of LEAFY and PTLF, a poplar (Populus) homolog of LEAFY/FLORICAULA, in transgenic poplar and Arabidopsis.

PTLF, the Populus trichocarpa homolog of LEAFY (LFY) and FLORICAULA, was cloned to assess its function in a dioecious tree species. In situ hybridization studies showed that the gene was expressed most strongly in developing inflorescences. Expression was also seen in leaf primordia and very young leaves, most notably in apical vegetative buds near inflorescences, but also in seedlings. Although ectopic expression of the PTLF cDNA in Arabidopsis accelerated flowering, only one of the many tested transgenic lines of Populus flowered precociously. The majority of trees within a population of 3-year-old transgenic hybrid Populus lines with PTLF constitutively expressed showed few differences when compared to controls. However, phenotypic effects on growth rate and crown development, but not flowering, were seen in some trees with strong PTLF expression and became manifest only as the trees aged. Competence to respond to overexpression of LFY varied widely among Populus genotypes, giving consistent early flowering in only a single male P. tremula x P. tremuloides hybrid and causing gender change in another hybrid genotype. PTLF activity appears to be subject to regulation that does not affect heterologously expressed LFY, and is dependent upon tree maturation. Both genes provide tools for probing the mechanisms of delayed competence to flower in woody plants.

Amino Acid Sequence↗

PubMed1996

Drought-Induced Xylem Dysfunction in Petioles, Branches, and Roots of Populus balsamifera L. and Alnus glutinosa (L.) Gaertn.

Variation in vulnerability to xylem cavitation was measured within individual organs of Populus balsamifera L. and Alnus glutinosa (L.) Gaertn. Cavitation was quantified by three different techniques: (a) measuring acoustic emissions, (b) measuring loss of hydraulic conductance while air-dehydrating a branch, and (c) measuring loss of hydraulic conductance as a function of positive air pressure injected into the xylem. All of these techniques gave similar results. In Populus, petioles were more resistant than branches, and branches were more resistant than roots. This corresponded to the pattern of vessel width: maximum vessel diameter in 1- to 2-year-old roots was 140 [mu]m, compared to 65 and 45 [mu]m in rapidly growing 1-year-old shoots and petioles, respectively. Cavitation in Populus petioles started at a threshold water potential of -1.1 MPa. The lowest leaf water potential observed was -0.9 MPa. In Alnus, there was no relationship between vessel diameter and the cavitation response of a plant organ. Although conduits were narrower in petioles than in branches, petioles were more vulnerable to cavitation. Cavitation in petioles was detected when water potential fell below -1.2 MPa. This value equaled midday leaf water potential in late June. As in Populus, roots were the most vulnerable organ. The significance of different cavitation thresholds in individual plant organs is discussed.

Journal Article↗

PubMed2003

Screening interspecific hybrids of Populus (P. ciliata x maximowiczii) using AFLP markers.

Hybrids of Populus ciliata x maximowiczii are very vigorous and outperform both the parents in growth performance and yield. Genetic evaluation of 24 of these interspecific hybrids along with the two mother trees ( Populus ciliata), and five male-parent ( Populus maximowiczii) genotypes was carried out using the AFLP marker assay. Eight AFLP primer combinations detected 428 markers, of which 280 (66%) were polymorphic. Genetic relationships within the samples were evaluated by generating the similarity matrix based on Jaccard's coefficient. The phenetic dendrograms, as well as the PCO plots, separated the hybrids and the two parent species into three distinct clusters. The hybrids grouped closer to the P. ciliata (female parent) cluster as compared to the P. maximowiczii (male parent) cluster. The hybrid cluster contained internal groupings, which correlated to some extent with growth performance. The four best performing hybrids (42m1, 65m1, 23m2, Cm2-5-20/91) formed a distinct sub-cluster. Data from a single primer combination was sufficient for distinguishing the hybrids from the parents and assigning paternity. The hybrids showed 22 markers that were absent in P. ciliata but were monomorphically present in all the hybrids, suggesting outcrossing and common paternity. Further, these 22 markers were found in all the P. maximowiczii genotypes confirming it as the male parent. These male-specific markers can be converted to SCAR markers and used for rapid screening of the P.ciliata x maximowiczii hybrids. The primer combination E-AAC x M-CAA was identified as most suitable for ascertaining true hybridity. AFLP proves to be a useful tool for screening of P. ciliata x maximowiczii hybrids at the early stages of development.

Genetic Markers↗

PubMed2004

Polyphenol oxidase overexpression in transgenic Populus enhances resistance to herbivory by forest tent caterpillar (Malacosoma disstria).

In order to functionally analyze the predicted defensive role of leaf polyphenol oxidase (PPO; EC 1.10.3.1) in Populus, transgenic hybrid aspen (Populus tremula x P. alba) plants overexpressing a hybrid poplar (Populus trichocarpa x P. deltoides) PtdPPO1 gene were constructed. Regenerated transgenic plants showed high PPO enzyme activity, PtdPPO1 mRNA levels and PPO protein accumulation. In leaf disk bioassays, forest tent caterpillar (Malacosoma disstria) larvae feeding on PPO-overexpressing transgenics experienced significantly higher mortality and reduced average weight gain compared to larvae feeding on control leaves. However, this effect was observed only when older egg masses were used and the resulting larvae showed reduced growth and vigor. In choice tests, no effect of PPO overexpression was detected. Although PPO in poplar leaves is latent and requires activation with detergents or trypsin for full enzymatic activity, in caterpillar frass the enzyme was extracted in the fully activated form. This activation correlated with partial proteolytic cleavage, suggesting that PPO latency and activation during digestion could be an adaptive and defense-related feature of poplar PPO.

Animals↗

PubMed2004

Identification and analysis of safener-inducible expressed sequence tags in Populus using a cDNA microarray.

Safeners are the chemicals used to protect plants from detrimental effects of herbicides, but their mode of action at the molecular level is not well understood. As an initial step towards understanding the molecular mechanism of safener action in trees, homologous genes in hybrid poplar (Populus nigra x Populus maximowiczii) that were induced by a safener were identified. We here describe the identification of differentially expressed genes in Populus that are induced by Concep-III, a herbicide safener. Expressed sequence tags (ESTs) enriched for transcriptionally induced genes were isolated by suppressive subtractive hybridization (SSH). The SSH library cDNA inserts were used to construct a cDNA microarray for high-throughput validation of the up-regulated expression of safener-induced genes. Single-pass and partial sequences of 1,344 safener-induced ESTs were assembled into 418 singletons and 328 clusters, but the putative functions of almost 53% of the ESTs are not known. Genes encoding proteins involved in all three different phases of safener action, viz., oxidation, conjugation, and sequestration, were found in the SSH library. Almost 75% of genes that showed greater than 2-fold expression upon safener treatment were redundant in the SSH library. The expression pattern for selected genes was validated by reverse transcription-polymerase chain reaction. A few safener-induced genes that were not previously reported to be induced by safeners, but which may have a role in herbicide metabolism, were identified. The newly identified genes could have potential for application in genetic engineering of plants for herbicide detoxification and tolerance.

Acetophenones↗

PubMed2004

[Proof of the indigenous nature of Populus alba L. in the western Mediterranean Basin].

Around the western Mediterranean Basin, the ecological status of Populus alba, whether indigenous or introduced, is controversial. This note presents new palaeobotanical data based on analyses of leaf imprints from a travertine formation located in southern France. This travertine presents two levels with Populus alba imprints. The oldest level is dated back by 14C to the Early Holocene, i.e., 8890 +/- 70 BP. This demonstrates that Populus alba is an autochthonous species of the southern-France vegetation, removing speculations reporting that its distribution area was greatly influenced by Roman civilization. Finally, we discuss this new data in regard to other Pleistocene and Holocene deposits circum the Mediterranean Basin and in Europe, where this species was identified.

Calcium Carbonate↗

PubMed2002

Diversity of cuticular wax among Salix species and Populus species hybrids.

The leaf cuticular waxes of three Salix species and two Populus species hybrids, selected for their ability to produce high amounts of biomass, were characterized. Samples were extracted in CH(2)Cl(2) three times over the growing season. Low kV SEM was utilized to observe differences in the ultrastructure of leaf surfaces from each clone. Homologous series of wax components were classified into organic groups, and the variation in wax components due to clone, sample time, and their interaction was identified. All Salix species and Populus species hybrids showed differences in total wax load at each sampling period, whereas the pattern of wax deposition over time differed only between the Salix species. A strong positive relationship was identified between the entire homologous series of alcohols and total wax load in all clones. Similarly strong relationships were observed between fatty acids and total wax load as well as fatty acids and alcohols in two Salix species and one Populus species hybrid. One Salix species, S. dasyclados, also displayed a strong positive relationship between alcohols and alkanes. These data indicate that species grown under the same environmental conditions produce measurably different cuticular waxes and that regulation of wax production appears to be different in each species. The important roles cuticular waxes play in drought tolerance, pest, and pathogen resistance, as well as the ease of wax extraction and analysis, strongly suggest that the characteristics of the cuticular wax may prove to be useful selectable traits in a breeding program.

Hybridization, Genetic↗

PubMed2003

Molecular analysis of natural populations of Populus nigra L intermingled with cultivated hybrids.

In this study six simple sequence repeats (SSR or microsatellites) were selected for their ability to fingerprint a total of 60 commercial clones of Populus deltoides Marsh. and Populus x canadensis Moench (typically derived from crosses between Populus nigra L and P. deltoides) and to characterize a natural population of P. nigra growing along the Ticino river in the North of Italy. Out of six SSRs used, four microsatellite loci were found to have alleles which were species-specific to P. deltoides and could therefore be used as markers for introgression of P. deltoides into P. nigra. In the studied region hybrid poplars and P. deltoides commercial clones are cultivated as monoclonal stands close to the area where black poplar has its natural habitat. SSR analysis was performed to investigate whether there was evidence of introgression between the natural population and the monoclonal plantations of hybrids and P. deltoides clones cultivated in the surrounding area. Three stages of the natural population were analysed: a group of old trees about a hundred years old, a younger population (aged 2-30 years) and the seedlings of three females of this population. Alleles specific to P. deltoides were detected only in the old cohort of the natural population, while no introgression was observed in the younger individuals and their progenies. These results were also confirmed by isozyme analysis of loci PGI-B, PGM and LAP-A, which were previously identified as diagnostic for P. nigra, P. deltoides and P.xcanadensis.

Forestry↗

PubMed2006

Distinct roles of cinnamate 4-hydroxylase genes in Populus.

Cinnamate 4-hydroxylase (C4H) catalyzes the conversion of cinnamate into 4-hydroxy-cinnamate, a key reaction of the phenylpropanoid pathway which leads to the biosynthesis of several secondary metabolites. C4H genes exist as a multigene family in various plant species. In order to understand the roles of individual C4H members, four C4H cDNAs (PtreC4H) were isolated from Populus tremuloides and three C4H loci (PtriC4H) were identified in the P. trichocarpa genome. The ability of Populus C4H isoforms to convert trans-cinnamate into p-coumaric acid was verified by the examination of yeast recombinant PtreC4H proteins. Populus C4H genes were expressed in various tissues, including developing xylem, phloem and epidermis; however, the expression patterns of individual members were different from each other. Sequential analysis of C4H promoters showed that the differential expression of C4H genes was associated with cis-acting regulatory elements such as box L, box P and H box, suggesting that the divergent C4H isoforms played distinct roles in the production of secondary metabolites. The involvement of specific C4H isoforms in the biosynthesis of guaiacyl and syringyl monolignols is discussed.

DNA, Plant↗

PubMed2006

UPSC-BASE--Populus transcriptomics online.

The increasing accessibility and use of microarrays in transcriptomics has accentuated the need for purpose-designed storage and analysis tools. Here we present UPSC-BASE, a database for analysis and storage of Populus DNA microarray data. A microarray analysis pipeline has also been established to allow consistent and efficient analysis (from small to large scale) of samples in various experimental designs. A range of optimized experimental protocols is provided for each step in generating the data. Within UPSC-BASE, researchers can perform standard and advanced microarray analysis procedures in a user-friendly environment. Background corrections, normalizations, quality-control tools, visualizations, hypothesis tests and export tools are provided without requirements for expert-level knowledge. Although the database has been developed primarily for handling Populus DNA microarrays, most of the tools are generic and can be used for other types of microarray. UPSC-BASE is also a repository of Populus microarray information, providing data from 21 experiments on a total of 407 microarray hybridizations in the public domain of the database. There are also an additional 10 experiments containing 347 hybridizations, where the automatically analysed data are searchable.

Databases, Genetic↗

PubMed2005

Allelic and population variation of microsatellite loci in aspen (Populus tremuloides).

To develop a robust basis for inferences about population genetics and evolution, this work assayed 192 aspens (Populus tremuloides) from 11 sites in Wisconsin, USA, for allelic and population variation at 16 microsatellite loci distributed across the Populus genome. Frequency distributions of fluorochrome-labeled alleles resolved by capillary electrophoresis were analyzed for relationships to repeat size and number. Population-level statistics were compared with those of other studies, especially in Populus. All loci were polymorphic, varying widely in the number of alleles per locus (mean = 8.25, range 2-20). Expected and observed heterozygosities were high (0.45 and 0.41, respectively), with little differentiation among populations (F(ST) = 0.006-0.045) and a moderate level of inbreeding (F(IS) = 0.09), intermediate among levels reported in studies based on isozymes. Contrary to several other reports, allele frequencies clustered tightly around the modal frequency, and the genetic diversity (measured as alleles per locus or as expected heterozygosity) was not related to either the repeat unit size or to the number of repeats.

Alleles↗

PubMed2026

Genus-Wide Pan-Genome Analysis of Populus bZIP Transcription Factors with Reanalysis of Public Salt-Stress Transcriptomes.

Basic leucine zipper (bZIP) transcription factors regulate plant development and stress responses, but their genus-wide diversity in Populus remains unclear. We analyzed 19 Populus genomes and retained 1764 bZIP proteins, including 21 independent new loci and four annotation corrections. Of these, 1762 were assigned to 79 orthologous gene groups (OGGs), comprising 43 core, 20 soft-core, 15 shell and one cloud OGG, of which 59 showed copy-number variation. Phylogenetic analysis assigned 74 representative pangenes to 13 subfamilies, with five remaining unclassified and motif patterns differing among subfamilies. Whole-genome duplication (WGD)/segmental duplication accounted for 81.0% of OGG-assigned proteins and contributed predominantly to the conserved component. Although 72.2% of bZIP proteins overlapped a transposable element within the gene body or 2-kb flanks, this proportion was modestly lower than in matched non-bZIP genes, and copy-number-variable OGGs showed no greater TE coverage than invariant OGGs. Among retained homologous comparisons, 97.6% had Ka/Ks ≤ 1, supporting predominant purifying selection. Across the heterogeneous public salt-stress RNA-seq datasets analyzed, no OGG showed a significant, directionally concordant response in at least two Populus taxa. These results reveal a conserved bZIP framework shaped mainly by ancient duplication alongside variable genomic contexts and transcriptional responses.

Populus↗

PubMed2003

[Impact of salt stress on peroxidase activity in Populus deltoides cambium and its consequence].

Studies on the impact of salt stress on the peroxidase (POD) activity in Populus deltoides cambium and on the anatomic characteristics of its secondary xylem indicated that the changes of POD activity caused by soil salinity stress behaved differently in dormant and growing period. In low salinity soil, the POD activity of dormant Populus deltoides showed the trend of increasing first, and then, decreasing as the soil salinity was rising gradually. Namely, with the rising of soil salinity in the range of 0.024-->0.094-->0.145%, the POD activity varied in the range of 83.7-->132.1-->63.2 units.min-1.g-1FW accordingly. However, in growing season, with the gradual increase of soil salinity from 0.036 to 0.289%, the POD activity decreased gradually from 405.2 to 107.2 units.min-1.g-1FW. There were regular changes in wood anatomic characteristics of Populus deltoides. Namely, with the increase of soil salinity 0.036-->0.125-->0.289%, the vessel diameters (VD) of both early wood and late wood varied accordingly in the range of 41.8-->56.6-->43.4 microns, and 29.1-->33.1-->33.1 microns, respectively. The vessel frequencies (VF) were 141.8-->113.8-->144.2 and 160.0-->134.8-->206.7 entries mm-2, respectively. Along with the gradual increase of soil salinity from 0.036 to 0.289%, the fiber length gradually decreased from 693.8 to 570.4 microns, and the fiber width decreased from 14.9 to 13.5 microns.

Ecology↗

PubMed2003

Identification of new aromatic cytokinins in Arabidopsis thaliana and Populus x canadensis leaves by LC-(+)ESI-MS and capillary liquid chromatography/frit-fast atom bombardment mass spectrometry.

A search for naturally occurring aromatic cytokinins (ARCKs) in Arabidopsis thaliana plants and Populus x canadensis leaves led to the discovery of four new plant hormone substances: 6-(2-methoxybenzylamino)purine (ortho-methoxytopolin, MeoT), 6-(3-methoxybenzylamino)purine (meta-methoxytopolin, MemT) (Fig. 1) and their 9-beta-D-ribofuranosyl derivatives. These substances were identified by liquid chromatography electrospray ionization mass spectrometry [LC (+)ESI-MS] and capillary-liquid chromatography/frit-fast atom bombardment-mass spectrometry [CapLC/frit-FAB-MS] after pre-column derivatization. The chemical structures were subsequently confirmed by chemical synthesis. Because of lack of heavy labelled internal standards, the endogenous levels of methoxytopolins in A. thaliana plants, Populus x canadensis leaves and samples derived from cultures of Agrobacterium tumefaciens strain GV3101 were determined by enzyme-linked immunosorbent assay (ELISA) of HPLC-fractionated extracts. While the levels of MeoT, MemT and their ribosides in A. thaliana shoots and Populus x canadensis leaves were relatively low (approximately 0.25-10 pmol g-1 FW for MeoT and MemT, respectively), the A. tumefaciens strain produced up to 600 times more of the newly identified substances. Cytokinin activity of methoxytopolines was demonstrated in three bioassays testing their ability to stimulate tobacco callus growth, to delay chlorophyll degradation in excised wheat leaves, and to induce betacyanin synthesis in Amaranthus caudatus var. atropurpurea cotyledons. Notably, their anti-senescing activity in the wheat leaf assay exceeded that of BAP and Z by almost 200%. Methoxytopolins are proposed to be new members of the biologically active aromatic cytokinin family, which might have specific physiological functions.

Journal Article↗

PubMed1990

Crown architecture of Populus clones as determined by branch orientation and branch characteristics.

Crown architecture, including branching pattern, branch characteristics and orientation of proleptic and sylleptic branches was studied in five poplar clones (Populus deltoides, P. trichocarpa and P. trichocarpa x P. deltoides hybrids), grown under intensive culture in the Pacific Northwest, USA. Branch characteristics measured were number, length, diameter, biomass and the angles of origin and termination. The results suggest that genotype has a major influence on crown architecture in Populus. Clonal differences in branch characteristics and branching patterns were found that resulted in striking differences in crown form and architecture. Branch angle and curvature differed significantly among clones, and among height growth increments within clones. Branch length and diameter were significantly correlated in all clones. Sylleptic branches and the considerable leaf area they carry have important implications for whole tree light interception, and thus, play a critical role in the superior growth and productivity of certain hybrid poplar clones. The considerable variation in branch characteristics implies a strong justification for including them in selection and breeding programs for Populus.

Journal Article↗