Across two phylogeographic breaks: Quaternary evolutionary history of a mountain aspen (Populus rotundifolia) in the Hengduan Mountains

Biogeographical barriers to gene flow are central to plant phylogeography.In East Asia,plant distribution is greatly influenced by two phylogeographic breaks,the Mekong-Salween Divide and Tanaka-Kaiyong Line,however,few studies have investigated how these barriers affect the genetic diversity of species that are distributed across both.Here we used 14 microsatellite loci and four chloroplast DNA fragments to examine genetic diversity and distribution patterns of 49 populations of Populus rotundifolia,a species that spans both the Mekong-Salween Divide and the Tanaka-Kaiyong Line in southwestern China.Demographic and migration hypotheses were tested using coalescent-based approaches.Limited historical gene flow was observed between the western and eastern groups of P.rotundifolia,but substantial flow occurred across both the Mekong-Salween Divide and Tanaka-Kaiyong Line,manifesting in clear admixture and high genetic diversity in the central group.Wind-borne pollen and seeds may have facilitated the dispersal of P.rotundifolia following prevalent northwest winds in the spring.We also found that the Hengduan Mountains,where multiple genetic barriers were detected,acted on the whole as a barrier between the western and eastern groups of P.rotundifolia.Ecological niche modeling suggested that P.rotundifolia has undergone range expansion since the last glacial maximum,and demographic reconstruction indicated an earlier population expansion around 600 Ka.The phylogeographic pattern of P.rotundifolia reflects the interplay of biological traits,wind patterns,barriers,niche differentiation,and Quaternary climate history.This study emphasizes the need for multiple lines of evidence in understanding the Quaternary evolution of plants in topographically complex areas.

Impacts of Defoliation on Morphological Characteristics and Non-Structural Carbohydrates of Populus talassica × Populus euphratica Seedlings

Leaves are important‘source’organs that synthesize organic matter,providing carbon sources for plant growth.Here,we used Populus talassica×Populus euphratica,the dominant species in ecological and timber forests,to simulate carbon limitation through artificial 25%,50%,and 75%defoliation treatments and explore the effects on root,stem,and leaf morphology,biomass accumulation,and carbon allocation strategies.At the 60th d after treat-ment,under 25%defoliation treatment,the plant height,specific leaf weight,root surface area and volume,and concentrations of non-structural carbohydrates in stem and root were significantly increased by 9.13%,20.00%,16.60%,31.95%,5.12%,and 9.34%,respectively,relative to the control.There was no significant change in the growth indicators under 50%defoliation treatment,but the concentrations of non-structural carbohydrates in the leaf and stem significantly decreased,showing mostly a negative correlation between them.The opposite was observed in the root.Under 75%defoliation treatment,the plant height,ground diameter,leaf number,single leaf area,root,stem,and total biomass were significantly reduced by 14.15%,10.24%,14.86%,11.31%,11.56%,21.87%,and 16.82%,respectively,relative to the control.The concentrations of non-structural carbohydrates in various organs were significantly reduced,particularly in the consumption of the starch concentrations in the stem and root.These results indicated that carbon allocation strategies can be adjusted to increase the con-centration of non-structural carbohydrates in root and meet plant growth needs under 25%and 50%defoliation.However,75%defoliation significantly limited the distribution of non-structural carbohydrates to roots and stems,reduced carbon storage,and thus inhibited plant growth.Defoliation-induced carbon limitation altered the carbon allocation pattern of P.talassica×P.euphratica,and the relationship between carbon reserves in roots and tree growth recovery after defoliation was greater.This study provides a theoretical basis for the comprehen-sive management of P.talassica×P.euphratica plantations,as well as a reference for the study of plantation car-bon allocation strategies in the desert and semi-desert regions of Xinjiang under carbon-limitation conditions.

Comprehensive Overview of Populus simonii Research in the Recent Years

As an important ecological tree species in northern China, Populus simonii plays a crucial role in maintaining ecological balance and promoting environmental sustainability. The academic community has conducted a series of in-depth studies on this species, covering key areas such as genomics, survival mechanisms, and genetic breeding. Through the analysis of the genomic structure and function of P. simonii, we have not only revealed the molecular basis for its adaptation to harsh environments but also identified key genes that promote its growth and resistance to pests and diseases. Furthermore, exploring the survival mechanisms of P. simonii has deepened our understanding of its stress resistance traits, including how it effectively copes with abiotic stresses such as drought, salinization, and heavy metal pollution. In genetic breeding, significant progress has been made through the application of modern biotechnology, improving the growth rate and wood quality of P. simonii and enhancing its environmental adaptability and disease resistance. These research findings have not only enriched our knowledge of the biological characteristics of P. simonii but also provided a solid scientific foundation for its application in ecological restoration, forestry production, and environmental management.

Wind-dispersed seeds blur phylogeographic breaks:The complex evolutionary history of Populus lasiocarpa around the Sichuan Basin

The strength of phylogeographic breaks can vary among species in the same area despite being subject to the same geological and climate history due to differences in biological traits.Several important phylogeographic breaks exist around the Sichuan Basin in Southwest China but few studies have focused on wind-dispersed plants.Here,we investigated the phylogeographic patterns and the evolutionary history of Populus lasiocarpa,a wind-pollinated and wind-dispersed tree species with a circum-Sichuan Basin distribution in southwest China.We sequenced and analyzed three plastid DNA fragments(ptDNA) and eight nuclear microsatellites(nSSRs) of 265 individuals of P.lasiocarpa from 21 populations spanning the entire distribution range.Distribution patterns based on nSSR data revealed that there are three genetic groups in P.lasiocarpa.This is consistent with the three phylogeographic breaks(Sichuan Basin,the Kaiyong Line and the 105°E line),where the Sichuan basin acts as the main barrier to gene flow between western and eastern groups.However,the distribution pattern based on ptDNA haplotypes poorly matched the phylogeographic breaks,and wind-dispersed seeds may be one of the main contributing factors.Species distribution modelling suggested a larger potential distribution in the last glacial maximum with a severe bottleneck during the last interglacial.A DIYABC model also suggested a population contraction and expansion for both western and eastern lineages.These results indicate that biological traits are likely to affect the evolutionary history of plants,and that nuclear molecular markers,which experience higher levels of gene flow,might be better indicators of phylogeographic breaks.

Assembly and analysis of the Populus deltoides mitochondrial genome:the first report of a multicircular mitochondrial conformation for the genus Populus

Genomics research of Populus deltoides,an important timber species that is widely planted worldwide,is an important part of poplar breeding.Currently,the nuclear and chloroplast genome of P.deltoides have been sequenced,but its mitochondrial genome(mitogenome)has not been reported.To further explore the evolution and phylogeny of P.deltoides,the mitogenome of P.deltoides I-69 was assembled using reads from Nanopore and Illumina sequencing platforms and found to consist of 802,637 bp and three circular chromosomes(336,205,280,841,and 185,591 bp)containing 58 genes(34 protein-coding genes,21 tRNA genes,and 3 rRNA genes).RNA analysis in combination with several species showed signifi cantly fewer RNA editingsites in the mitogenomes of poplar and other angiosperms than in gymnosperms.Sequence transfer analysis showed extensive mitogenome rearrangements in Populus species,and with evolution from lower to higher plants,tRNA transfer from chloroplasts to mitochondria became increasingly frequent.In a phylogenetic analysis,the evolutionary status of P.deltoides was determined,and the section Populus was supported.Our results based on the fi rst report of a multicircular conformation of the Populus mitogenome provide a basis for further study of the evolution and genetics of P.deltoides and other Populus species and for breeding programs.

Trunk volume estimation of irregular shaped Populus euphratica riparian forest using TLS point cloud data and multivariate prediction models

Background: Trunk volume(Vt) is an essential parameter for estimating forest stand volume, biomass, and carbon sequestration potential. As the dominant tree species in desert riparian forests, Euphrates poplar(Populus euphratica) has a high proportion of irregularly shaped tree trunks along the Tarim River, NW China, where the habitat is very fragile owing to long-term water stress. This causes uncertainty in estimation accuracy as well as technical challenges for forest surveys. Our study aimed to acquire P. euphratica Vtusing terrestrial laser scanning(TLS) and to establish a species-specific Vtprediction model.Methods: A total of 240 individual trees were measured by TLS multiple-station in 12 sampling plots in three sections along the lower reaches of the Tarim River. Vtwas calculated by a definite integration method using trunk diameters(Di) at every 0.1-m tree height obtained from TLS, and all data were split randomly into two sets:70% of data were used to estimate the model parameter calibration, and the remaining 30% were used for model validation. Sixteen widely used candidate tree Vtestimation models were fitted to the TLS-measured Vtand tree structural parameter data, including tree height(H), diameter at breast height(DBH), and basal diameter(BD). All model performances were evaluated and compared by the statistical parameters of determination coefficient(R^(2)),root mean square error(RMSE), Bayesian information criterion(BIC), mean prediction error(ME), mean absolute error(MAE), and modeling efficiency(EF), and accordingly the best model was selected.Results: TLS point cloud reflection intensity(RI) has advantageous in the extraction of data from irregular tree trunk structures. The P. euphratica tree Vtvalues showed obvious differences at the same tree height(H). There was no significant correlation between Vtand H(R^(2)=0.11, P < 0.01), which reflected the irregularity of P. euphratica trunk shape in the study area. Among all the models, model(14): Vt=0.909DBH1.184H0.487BD0.836(R^(2)=0.97, RMSE=0.14) had the best prediction capability for irregularly shaped Vtwith the highest R^(2), BIC(-37.96), and EF(0.96), and produced a smaller ME(0.006) and MAE(1.177) compared to other models. The prediction accuracy was 93.18%.Conclusions: TLS point cloud RI has a potential for nondestructively measuring irregularly shaped trunk structures of P. euphratica and developed Vtprediction models. The multivariate models more effectively predicted Vtfor irregularly shaped trees compared to one-way and general volume models.

Genome-wide identification and characterization of ACBP gene family in Populus reveal salinity alkali-responsive profiles

Acyl-CoA-binding proteins(ACBPs)are important for the transport of acyl groups for macro molecular biosynthesis involved in plant growth,development,and diverse stress(e.g.,cold,drought,salinity,and heavy metals)responses.Here,we report the phylogeny and characteristics of the ACBP family in the woody plant Populus trichocarpa.Eight genes encoding ACBP proteins were identified,and they are distributed on eight chromosomes in P.trichocarpa.These PtACBP genes were divided into four subgroups according to gene structure,conserved motifs and phylogenetic relationship.Promoter analysis revealed that cis-elements were related to stress response,phytohormone response,and physical and reproductive growth regulation.Expression levels of PtACBP genes varied among different organs,with the highest expression in leaves and the lowest in stems.Quantitative real-time PCR(qRT-PCR)analysis showed that under salinity-alkali stresses(i.e.,200 mM NaCl,75 mM Na2CO3,and 100 mM NaHCO3),four(PtACBP1,PtACBP3,PtACBP4 and PtACBP8)of eight PtACBP genes were significantly induced in roots and leaves.These data provide a comprehensive analysis of the ACBPs family in P.trichocarpa,which could be useful for gene function analyses.

Genome-Wide Analysis of the KANADI Gene Family and Its Expression Patterns under Different Nitrogen Concentrations Treatments in Populus trichocarpa

KANADI(KAN)is a plant-specific gene that controlled the polarity development of lateral organs.It mainly acted on the abaxial characteristics of plants to make the lateral organs asymmetrical.However,it had been less identified in woody plants.In this study,the members of the KAN gene family in Populus trichocarpa were identified and analyzed using the bioinformatics method.The results showed that a total of 8 KAN family members were screened out,and each member contained the unique GARP domain and conserved region of the family proteins.Phylogenetic analysis and their gene structures revealed that all KAN genes from P.trichocarpa,Arabidopsis thaliana,and Nicotiana benthamiana could be divided into four subgroups,while the eight genes in P.trichocarpa were classified into three subgroups,respectively.The analysis of tissue-specific expression indicated that PtKAN1 was highly expressed in young leaves,PtKAN6 was highly expressed in young leaves and mature leaves,PtKAN2,PtKAN5,and PtKAN7 were highly expressed in nodes and internodes,PtKAN8 was highly expressed in roots,and PtKAN3 and PtKAN4 showed low expression levels in all tissues.Among them,PtKAN2 and PtKAN6,and PtKAN4 and PtKAN5 might have functional redundancy.Under high nitrogen concentrations,PtKAN2 and PtKAN8 were highly expressed in mature stems and leaves,respectively,while PtKAN4,PtKAN5,and PtKAN7 were highly expressed in roots.This study laid a theoretical foundation for further study of the KAN genemediated nitrogen effect on root development.

Fine Root Distribution Characteristics of Populus cathayana Plantations at Different Ages in Alpine Sandy Land

[Objectives]The paper was to study the fine root distribution characteristics of Populus cathayana plantations at different ages in alpine sandy land.[Methods]With 5,10,15,20,and 25 years old P.cathayana plantation in the eastern margin of Gonghe Basin,Qinghai Province as the research objects,fine roots were collected by root core drilling method,and the differences of fine root biomass,root length density,average diameter and root tip number at the soil depths of 0-20,20-40,40-60,60-80 and 80-100 cm were analyzed.[Results]The total biomass density of P.cathayana plantation was mainly distributed in the soil layer of 0-60 cm,accounting for 76%of the entire soil layer,and its value increased with the increase in forest age.With the increase in different forest ages,the root length density,average diameter and root tip number of living fine roots in the soil layer of 0-60 cm accounted for 74%-81%of the entire soil layer,and the proportions in the soil layers of 60-80 and 80-100 cm were 9%-11%.The biomass density,root length density,average diameter and root tip number of living and dead fine roots of P.cathayana plantation increased with the increase of forest age.The root length density,average diameter and root tip number of P.cathayana fine roots showed a linear function change trend with the growth of forest age,which could be described by the linear function equation y=ax+b(a>0).The analysis results showed that the root length density,average diameter and root tip number of P.cathayana were significantly correlated with the total biomass density of fine roots,and the root length density and average diameter had an extremely positive correlation with the total biomass density.[Conclusions]In the future,P.cathayana plantation should be properly tended to promote the development of fine roots and maximize its ecological benefits.

Two response patterns to negative environmental changes:Cases from Populus and Metasequoia

Traditionally,plant distribution is thought to be closely related to environmental factors.But recently,it is found that Populus,quite different from other plant taxa,adapted to negative environmental changes,and successfully migrated to different climate zones from its origin places of warm temperate zone.Conversely,Metasequoia is gradually tending to extinction from the Miocene to Quaternary.Based on above contrary cases,two response patterns of plant to negative environmental changes are proposed.One is active adaptation represented by Populus,the other is passive adaptation represented by Metasequoia.The plants of passive strategy characterized for desert prevention might be easily replaced by those of active strategy characterized for desert utilization.Fast growing plants,such as Populus with characteristics of drought and salt tolerance,wind and sand resistance,are selected in Tarim Basin in southern Xinjiang,China,as a good example of desert utilization in the construction of new highways and towns,not only serve as farmland shelterbelt in sandy area.In addition,Populus with high-altitude and cold adaptation has also been selected as an ideal tree planted in Tibet.Therefore,the idea of using Populus as one of the preferred pioneer trees to colonize Mars is proposed.

Observations on bud burst phenology in a field trial established with Poplar (Populus spp.)

Bud flushing is very important for the survival and growth of trees, a phenomenon matched each year with the annual course of temperature and the timing of bud flushing in the spring. Essentially it represents a serious ecological and evolutionary tradeoff between survival and growth. The most suitable timing of bud burst permits trees to begin growth sufficiently early to take advantage of favorable spring conditions, but late enough to decrease the risks of tissue damage from late frost. In the present study bud burst spring phenology of poplar （Populus tremula and P. tremuloides） from eight different provenances, originating from Eu- rope and the USA, was observed during March and April, 2009. The experimental plot was located at Solling, Germany （51~44＇0＂ N, 9036＇0＇＇ E）. A six stage subjective scoring system of bud burst phenology was used to identify the phenological stages of the seed- lings, where each plant was observed twice a week. The aim of the study was to predict phenotypic variation in poplar, originating from regions between 42~ and 60~ N latitude, growing in similar environments. Timing of bud flushing of poplar was recorded. It was found that seedlings of provenance 3, which originated from 42.35~ N latitude, started and completed flushing significantly earlier than those of other provenances, while seedlings of provenance 5, originating from 54.29~ N latitude, started flushing very late and only a few plants reached top scoring at the end of the experimental period. Analysis of variance showed statistically highly signifi- cant differences （p 〈 0.05） in bud flushing among the provenances. The correlation between scoring and flushing periods was very strong within provenances although the flushing pattern differed among provenances （origin of the planted seedlings）. Bud flushing showed a negative correlation with the origin of the planted seedlings. Given the field experience gained with this experiment, it is recommended that seedlings from provenances 5 and 8 could be used for future plantations where late frost may be a problem for the young shoots of seedlings.

A new diterpenoid from the stem bark of Populus davidiana

A new diterpenoid, named populusol A （1）, was isolated from the methanolic extraction of the stem bark of Populus davidiana. The structure was elucidated on the basis of extensive 1D and 2D NMR as well as HRFAB-MS spectroscopic analysis.

胡杨(Populus euphratica)异形叶叶片内源激素特征研究

通过野外调查结合室内分析,对胡杨异形叶叶片4种内源激素含量在胡杨不同个体发育阶段以及在树冠垂直空间的变化进行研究。结果表明:(1)胡杨不同发育阶段个体叶片平均叶形指数随着树龄的增大逐渐减小,且当植株树龄相差大于4年以上即存在显著差异;叶形指数均表现为从树冠底端到顶端逐渐减小,且顶端与底端存在显著差异。(2)胡杨成熟叶片IAA含量和IAA/ABA比值的变化趋势是随树龄的增加和树冠的增高而减小,而ZR、ABA含量和GA3/IAA,ZR/IAA比值的变化趋势则相反。研究认为,叶片内源激素含量随叶形的变化反映了胡杨适应干旱荒漠环境的生理调节。

Structural Characteristics and Eco-adaptability of Heteromorphic Leaves of Populus euphratica

The microstructural and ultrastructural traits of three kinds of typical leaves of Populus euphratica Olive, including lanceolate, broad-ovate and dentate broad-ovate leaves, were studied by using electron microscope and optical microscope. The re- sults showed that with the leaves changing from lanceolate shape to dentate broad-ovate shape, their structure obviously tended to be xeromorph: developed palisade tissue, undeveloped spongy tissue, thick cutin layer and sunken stomas. The amount of mitochondria tended to be increased, and the shape of chloroplasts varied from regular spindle to irregular rotundity or oval. The leaves were cov- ered with wax without cilium, and the stomas on the upper and lower epidermis of the leaves opened unevenly. The stomas on the lower epidermis were deeper than those on the upper epidermis under the scanning electron microscope. The results implied that the structural characteristics of the diversiform-leaves of P. euphratica are related to its eco-adaptability.

Stand structure and height-diameter relationship of a degraded Populus euphratica forest in the lower reaches of the Tarim River, Northwest China

Understanding stand structure and height-diameter relationship of trees provides very useful information to establish appropriate countermeasures for sustainable management of endangered forests. Populus euphratica, a dominant tree species along the Tarim River watershed, plays an irreplaceable role in the sustainable development of regional ecology, economy and society. However, as the result of climate changes and human activities, the natural riparian ecosystems within the whole river basin were degraded enormously, particularly in the lower reaches of the river where about 320 km of the riparian forests were either highly degraded or dead. In this study, we presented one of the main criteria for the assessment of vitality of P. euphrafica forests by estimating the defoliation level, and analyzed forest structure and determined the height-diameter （height means the height of a tree and diameter means the diameter at breast height （DBH） of a tree） relationship of trees in different vitality classes （i.e. healthy, good, medium, senesced, dying, dead and fallen）. Trees classified as healthy and good ac- counted for approximately 40% of all sample trees, while slightly and highly degraded trees took up nearly 60% of total sample trees. The values of TH （tree height） and DBH ranged from 0-19 m and 0-125 cm, respectively. Trees more than 15 m in TH and 60 cm in DBH appeared sporadically. Trees in different vitality classes had different distribution patterns. Healthy trees were mainly composed more of relatively younger trees than of degraded tress. The height-diameter relationships differed greatly among tress in different vitality classes, with the coefficients ranging from 0.1653 to 0.6942. Correlation coefficients of TH and DBH in healthy and good trees were higher than those in trees of other vitality classes. The correlation between TH and DBH decreased with the decline of tree vitality. Our results suggested that it might be able to differentiate degraded P. euphratica trees from healthy trees by determining the height-diameter correlation coefficient, and the coefficient would be a new parameter for detecting degradation and assessing sustainable management of floodplain forests in arid regions. In addition, tree vitality should be taken into account to make an accurate height-diameter model for tree height prediction.

Responses of germination and radicle growth of two Populus species to water potential and salinity

Abstract The effects of water potential, NaCl and Na2SO4 on germination and radicle growth of two riparian tree species, Populus euphratica Oliv. and P. pruinosa Schrenk （Salicaceae）, were tested. Growth chamber studies revealed an optimum temperature range for seed germination of both species between 15-35℃. The final germination percentage of both species decreases with decreasing water potential in all types of solution applied in the experiments. P. pruinosa was less tolerant to low ψw stress than P. euphratica, especially in salt solutions. Germination percentages fell below 20% for P. pruinosa at -0.6 MPa （NaCl） or -0.4 MPa （Na2SO4） and for P. euphratica at -1.2 MPa （NaCl） or -0.6 MPa （Na2SO4）. Radicle growth of both species was inhibited by high concentrations of PEG1 NaCl and Na2SO4. However, growth was enhanced at -0.13 and -0.29 MPa in PEG or at -0.13 MPa in NaCl solutions compared to distilled water. Radicle growth of P. euphratica was higher than that of P pruinosa. Germination and radicle growth of both species exhibited ion toxicity. Na2SO4 was more toxic than iso-osmotic solutions of NaCl. Radicle growth proved to be more sensitive than seed germination. Thus, flooding does not only yield the necessary soil moisture for germination but also favors seedling establishment of both species through leaching of salts from the soil surface. The different sensitivity of the species during their early growth stages might, moreover, contribute to the observed differences in their distribution in the Talim Basin （northwest China）.

Drought stress tolerance analysis of Populus ussuriensis clones with different ploidies

The selection of drought-tolerant plants is an important aspect of plant breeding.We studied physiological and biochemical mechanisms of different ploidies of Populus ussuriensis Kom.that relate to drought stress tolerance.We used a 5%(v/v)polyethylene glycol(PEG-6000)solution to simulate drought stress.We recorded leaf phenotypes including color,dry area and curl degree.We evaluated sequential variations in some drought stress tolerance-related physiological and biochemical indices and compared these among diploid clones(CK),triploid clones(T12)and tetraploid clones(F20).T12 leaves exhibited slightly more drought stress damage than CK and F20 leaves.CK leaves suffered the most severe drought stress damage.The physiological and biochemical indices of the different ploidies differed significantly 12 days after drought stress treatment.The activities of superoxide dismutase,peroxidase,catalase and proline in the triploid(T12)leaves were the highest.The relative electric conductivity and malondialdehyde content of T12 leaves were the lowest.The index values of F20 were between those ofthe diploid and triploid.In consideration of these results,the drought resistance of the three different ploidies of P.ussuriensis can be ranked as T12>F20>CK.We speculate that the gene expression patterns of polyploid clones of poplar will change after genome doubling and that some of the drought stress tolerance-related physiological and biochemical indices will be improved,resulting in greater drought tolerance of polyploid clones.

Nighttime transpiration of Populus euphratica during different phenophases

Evidence exists of nighttime transpiration and its potential impact on plant/water relations for species in a diversity of ecosystems. However, relevant data related to typical desert riparian forest species remains limited Accordingly, we measured sap flow velocity of Populus euphratica using the heat ratio method between 2012 and2014. Nocturnal stem sap flow was separated into nighttime and stem refilling using the ‘‘forecasted refilling''method. Nighttime transpiration was observed for each phenophase. The highest value was during the full foliation period but lowest during leaf expansion and defoliation periods. The contribution of nighttime transpiration to daytime transpiration was an average of 15% but this was comparatively higher during the defoliation period. Relationships between nighttime transpiration, vapor pressure deficits, and air temperatures were more closely associated than with wind speed in all phenophases. Moreover, we found that nighttime transpiration linearly correlated to vapour pressure deficit during the first and the full foliation periods, but nighttime transpiration showed exponential correlations to air temperatures during the same phenophases. Additionally, environmental drivers of transpiration were significantly different between nighttime and daytime(P \ 0.05). Driving forces behind nighttime transpiration were characterized by many factors, and integrated impacts between these multiple environmental factors were complex. Future studies should focus on these integrated impacts on nighttime transpiration, and the physiological mechanisms of nighttime transpiration should be investigated, given that this could also influence its occurrence and magnitude during different phenophases.

Isolation and characterization of two genes encoding polygalacturonase-inhibiting protein from Populus deltoides

Polygalacturonase-inhibiting proteins （PGIPs） are extracellular proteins that belong to the leucine-rich repeat （LRR） protein superfamily. PGIPs inhibit fungal polygalacturonases （PGs） and promote accumulation of oligogalacturonides, which activate plant defense responses. PGIPs play important roles in resistance to infection of pathogens. In this study, reverse transcriptase-polymerase chain reaction （RT-PCR） and RNA ligase-mediated rapid amplification of cDNA ends （RLM-RACE） were used to isolate the full-length PGIP cDNA from Populus deltoides （GenBank accession no. of PdPGIP2 and PdPGIP4：EF684913 and EF684912）. Domain analysis revealed that the deduced amino acid sequences of PdPGIP2 and PdPGIP4 had a typical PGIP topology. Phylogenetic analysis of known PGIPs indicated that the two PdPGIPs were clustered to the defense-related PGIP clade. Using real-time RT-PCR, the expression patterns of the two PdPGIPs following treatment with a fungal pathogen and defense-related signaling molecules were studied. The expression levels of PdPGIP2 and PdPGIP4 were both up-regulated when inoculated with the phytopathogenic fungus Marssonina brunnea. Therefore, it was proposed that the two PGIPs might be involved in the resistance to Marssonina brunnea in P. deltoides.