Populus Euphratica Research Articles

Streptomyces arboris sp. nov., isolated from Populus euphratica wetland soil.

A novel actinobacterial strain (TRM 68085T) was isolated from soil of Populus euphratica wetland. A polyphasic approach was used to study the taxonomy of TRM 68085T and the results showed a range of phylogenetic and chemotaxonomic properties consistent with those of the genus Streptomyces. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain TRM 68085T showed the highest similarity value to Streptomyces capitiformicae 1H-SSA4T (98.6 %), and phylogenetically clustered with Streptomyces kanasensis ZX01T(97.5 %) and Streptomyces ipomoeae NBRC 13050T (97.4 %). The genomic DNA G+C content of strain TRM 68085T based on the genome sequence was 71.4 mol%. The levels of DNA-DNA relatedness between the genome of the isolate and its nearest phylogenetic neighbours, S. capitiformicae 1H-SSA4T, S. kanasensis ZX01T and S. ipomoeae NBRC 13050T, were 19.2±0.4, 21.8±0.5 and 19.3±0.6 %, respectively. Chemotaxonomic data revealed that strain TRM 68085T possessed MK-9(H6) and MK-9(H8) as the predominant menaquinones. ll-Diaminopimelic acid and a small amount of meso-diaminopimelic acid were the diagnostic diamino acids. Ribose, xylose, glucose and galactose were the whole-cell sugars. The major cellular fatty acids were C16 : 0 (25.4 %) and iso-C16 : 0 (18.3 %). On the basis of these genotypic and phenotypic data, it is concluded that strain TRM 68085T represents a novel species of the genus Streptomyces, for which the name Streptomyces arboris sp. nov. is proposed. The type strain is TRM 68085T (=CCTCC AA2019031T=LMG 31492T).

Metagenomics Reveal Correlations Between Microbial Organisms in Soils and the Health of Populus euphratica

Biological diversity plays an important role in the stability of ecosystems. The Mu Us Desert (MUD), located in Northern China, is an aeolian desert. Although it has been governed by a series of ecological restoration programs, the MUD still has limited biological diversity. Populus euphratica (P. euphratica), a xerophytic plant, has great potential to improve the biological diversity of the MUD. However, the survival rate of P. euphratica in the MUD has been very low. The current study tried to explore the mechanism of the high death rate of P. euphratica in the microbiome perspective. The correlation study between soil community composition and soil properties showed that water-filled pore space (WFPS), pH, EC, AP, NO3–, and NH4+ possess higher potential to change the bacterial community (18%) than the fungal community (9%). Principal coordinate analysis indicated that the composition of both bacteria (Proteobacteria and Bacteroidetes) and fungi (Ascomycota) in the root soil can be increased by P. euphratica. By systematically comparing between the fungal diversity in the root soil around P. euphratica and the pathogenic fungus extract from the pathogenic site of P. euphratica, we found that the high death rate of P. euphratica was associated with specific pathogenic fungus Alternaria alternate and Didymella glomerata. In addition, the microbiome composition analysis indicated that P. euphratica planting could also influence the portions of bacteria community, which also has great potential to lead to future infection. However, as the extraction and separation of bacteria from plants is challenging, the correlation between pathogenic bacteria and the high death rate of P. euphratica was not studied here and could be explored in future work.

ABF3 enhances drought tolerance via promoting ABA-induced stomatal closure by directly regulating ADF5 in Populus euphratica.

Water availability is a main limiting factor for plant growth, development, and distribution throughout the world. Stomatal movement mediated by abscisic acid (ABA) is particularly important for drought adaptation, but the molecular mechanisms in trees are largely unclear. Here, we isolated an ABA-responsive element binding factor, PeABF3, in Populus euphratica. PeABF3 was preferentially expressed in the xylem and young leaves, and was induced by dehydration and ABA treatments. PeABF3 showed transactivation activity and was located in the nucleus. To study its functional mechanism in poplar responsive to drought stress, transgenic triploid white poplars (Populus tomentosa 'YiXianCiZhu B385') overexpressing PeABF3 were generated. PeABF3 overexpression significantly enhanced stomatal sensitivity to exogenous ABA. When subjected to drought stress, PeABF3 overexpression maintained higher photosynthetic activity and promoted cell membrane integrity, resulting in increased water-use efficiency and enhanced drought tolerance compared with wild-type controls. Moreover, a yeast one-hybrid assay and an electrophoretic mobility shift assay revealed that PeABF3 activated the expression of Actin-Depolymerizing Factor-5 (PeADF5) by directly binding to its promoter, promoting actin cytoskeleton remodeling and stomatal closure in poplar under drought stress. Taken together, our results indicate that PeABF3 enhances drought tolerance via promoting ABA-induced stomatal closure by directly regulating PeADF5 expression.

Stomatal Sensitivity to Vapor Pressure Deficit and the Loss of Hydraulic Conductivity Are Coordinated in Populus euphratica, a Desert Phreatophyte Species.

There are considerable variations in the percentage loss of hydraulic conductivity (PLC) at mid-day minimum water potential among and within species, but the underpinning mechanism(s) are poorly understood. This study tested the hypothesis that plants can regulate leaf specific hydraulic conductance (Kl) via precise control over PLC under variable ΔΨ (water potential differential between soil and leaf) conditions to maintain the −m/b constant (−m: the sensitivity of stomatal conductance to VPD; b: reference stomatal conductance at 1.0 kPa VPD), where VPD is vapor pressure deficit. We used Populus euphratica, a phreatophyte species distributed in the desert of Northwestern China, to test the hypothesis. Field measurements of VPD, stomatal conductance (gs), gs responses to VPD, mid-day minimum leaf water potential (Ψlmin), and branch hydraulic architecture were taken in late June at four sites along the downstream of Tarim River at the north edge of the Taklamakan desert. We have found that: 1) the −m/b ratio was almost constant (=0.6) across all the sites; 2) the average Ψ50 (the xylem water potential with 50% loss of hydraulic conductivity) was −1.63 MPa, and mid-day PLC ranged from 62 to 83%; 3) there were tight correlations between Ψ50 and wood density/leaf specific hydraulic conductivity (kl) and between specific hydraulic conductance sensitivity to water potential [d(ks)/dln(−Ψ)] and specific hydraulic conductivity (ks). A modified hydraulic model was applied to investigate the relationship between gs and VPD under variable ΔΨ and Kl conditions. It was concluded that P. euphratica was able to control PLC in order to maintain a relatively constant −m/b under different site conditions. This study demonstrated that branchlet hydraulic architecture and stomatal response to VPD were well coordinated in order to maintain relatively water homeostasis of P. euphratica in the desert. Model simulations could explain the wide variations of PLC across and within woody species that are often observed in the field.

Genome-wide association studies of callus differentiation for the desert tree, Populus euphratica.

Callus differentiation is a key developmental process in plant regeneration from cells. A better understanding of the genetic architecture of callus differentiation timing can help improve tissue transformation and the efficiency of artificial propagation. In this study, we investigated genotypic variation in callus differentiation capacity among 297 diverse P. euphratica trees sampled from a natural population. We employed a genome-wide association study (GWAS) of binary and growth-based parameters to identify loci and characterize the genetic architecture and genetic network underlying regulation of callus differentiation in P. euphratica. The results of this GWAS experiment suggested potential associations controlling whether the callus could differentiate and the process of callus differentiation. We identified multiple significant quantitative trait loci (QTLs), including the genes LOG1 and LOG7 and a locus containing WOX1. We reconstructed a genetic network that visualizes how each QTL interacts uniquely with other variants, and several core QTLs were detected that are involved in the degree of callus differentiation, providing potential targets for selection. This study represents one of the first to identify genetic variants affecting callus differentiation in a forest tree. Our results suggest that callus differentiation may be a typical qualitative-quantitative trait controlled by a major gene as well as polygenes across the genome of P. euphratica. This GWAS will help to design more complex and specific molecular tools for systematically manipulating organ regeneration.

Enhancing the positive effects of ecological water conservancy engineering on desert riparian forest growth in an arid basin

In arid areas, ecological water conservancy engineering influences vegetation growth by altering river flooding dynamics in addition to the depths of groundwater. However, few studies have explored how to develop the optimal floodwater and groundwater regulation strategies that take into account both ecological water supply and vegetation growth. Therefore, the aim of the present study was to propose the suitable regulation strategies by revealing that the plant growth responses to hydrological variation (i.e., the flooding and groundwater depth). Based on two growth indicators (i.e., the time-integrated normalized difference vegetation index (TINDVI) for plant canopy growth and the tree-ring chronology for trunk growth) in the middle reaches of the Tarim River, and water consumption, water discharge from ecological sluices for flooding, and groundwater depth data, after the implementation of an scheme in ecological water conservancy engineering, the ecological water transport efficiency, tree-ring chronology in Populus euphratica, and TINDVI improved by 12.4%, 5.6% and 4.2%, respectively. Notably, the tree-ring chronology increased with a decrease in water consumption. Due to a significant correlation between tree-ring chronology and TINDVI, the tree-ring chronology could be used to reconstruct the canopy growth in the case of the unavailability of monitoring data. There were significant correlations between TINDVI and groundwater depth in June–October, between tree-ring chronology and groundwater depth in October, and between water discharge from ecological sluices and vegetation growth in September. In addition, there were high correlation and sensitivity between trunk growth and water discharge (compared to groundwater depth), and between canopy growth and groundwater depth (compared to water discharge). Based on the above results, potentially sustainable groundwater depths (-2.3 to −3.7 m) and discharge water quantities (3.53–5.90 × 108 m3) and regimes were proposed that could further promote the vegetation growth.

Species-specific responses to drought, salinity and their interactions in Populus euphratica and P. pruinosa seedlings

Abstract Aims Drought and salinity are severe abiotic stress factors, which limit plant growth and productivity, particularly in desert regions. In this study, we employed two desert poplars, Populus euphratica Oliver and Populus pruinosa Schrenk seedlings, to compare their tolerance to drought, salinity and combined stress. Methods We investigated species-specific responses of P. euphratica and P. pruinosa in growth, photosynthetic capacity and pigment contents, nonstructural carbohydrate concentrations, Cl− allocation, osmotic regulation and the accumulation of reactive oxygen species (ROS) under drought, salinity and the combined stress. Important Findings Populus pruinosa exhibited greater growth inhibitory effects, photosynthesis decline, stomatal closure and ROS accumulation, and lower antioxidant enzyme activities and osmotic regulation compared with P. euphratica under drought, salinity and especially under their combined stress. On the other hand, salt-stressed P. euphratica plants restricted salt transportation from roots to leaves, and allocated more Cl− to coarse roots and less to leaves, whereas salt-stressed P. pruinosa allocated more Cl− to leaves. It was shown that there is species-specific variation in these two desert poplars, and P. pruinosa suffers greater negative effects compared with P. euphratica under drought, salinity and especially under the combined stress. Therefore, in ecological restoration and afforestation efforts, species-specific responses and tolerances of these two poplar species to drought and salinity should be considered under climate change with increasing drought and soil salinity developing.

Inner Asian agro-pastoralism as optimal adaptation strategy of Wupu inhabitants (3000–2400 cal BP) in Xinjiang, China

Exploring ancient socio-economic adaptation is a basic issue of human-environment interaction. Xinjiang in northwest China is a region of high geographic diversity. Past human adaptations to this arid marginal area is a current focus of research interest but still lacks in-depth study. This article presents data from the Wupu Cemetery, located in the extremely arid Hami Basin in the eastern Tianshan Mountains. Archaeobotanical analysis is used to reconstruct the local environment niche and the subsistence economy of inhabitants. Radiocarbon dating results indicate the cemetery was occupied between 3000 and 2400 cal BP, during the late Bronze Age and early Iron Age. In total 16 species of the plant remains are identified, including four cereal crops, foxtail millet ( Setaria italica), broomcorn millet ( Panicum miliaceum), naked barley ( Hordeum vulgare var. coeleste), wheat ( Triticum aestivum) and 12 wild types. The riparian plant Populus euphratica and aquatic plant Typha sp. indicate inhabitants lived in an oasis near the cemetery. Environmental interpretation of this data compares well with other seven sites in arid southern Xinjiang. In addition to faunal remains from the site, it is assumed that a flexible system of multi-crop farming and herding was the subsistence pattern around Wupu. This system was widespread across Inner Asia and appears to have played a central role in adapting to different marginal environments during the Bronze Age and Iron Age.

Nesting and foraging behavior of Xylocopa valga in the Ejina Oasis, China.

Xylocopa valga is extinct in Latvia and Lithuania and is critically endangered in Poland, and its distribution in the Ejina Oasis, China, is currently unknown. Studies on the biology of X. valga are scarce, and thus, conservation efforts for this species are currently limited. Here, we investigated the morphological characteristics, nest architecture, nest structure and food type of offspring in the nest cells of X. valga. This research was conducted in the Populus euphratica forest reserve in the Ejina Oasis, China, between July 2014 and June 2019. The primary investigation methods included visual inspection, photography, observation and measurements of nest anatomy, and examination of pollen stores by microscopy. We found that in the Ejina Oasis, China, X. valga builds its nests in the dead wood of P. euphratica. X. valga is univoltine. Its lifestyle varies from solitude to symbiosis. When many females nest near each other, several females may share a single nest entrance, based on which they build their own cells. The nests are branched. According to our results, there is a significant difference between the thickness of the inner cell partition and that of the outermost cell partition in the branched tunnel. In the P. euphratica forest area, the food for the progeny of X. valga is mainly composed of the pollen and nectar of Sophora alopecuroide and Populus euphratica. Therefore, X. valga and S. alopecuroides exhibit close ecological interactions in the P. euphratica forest ecosystem.

<p class="Body"><strong>Two new <em>Aceria</em> species (Acari: Eriophyidae) from Lorestan province of Iran</strong></p>

During a survey of the eriophyoid mites in Lorestan province of Iran two new eriophyoid mites described and illustrated: Aceria poldokhtariensis Lotfollahi & Bahirai sp. nov. from Populus euphratica Oliv. (Salicaceae) and Aceria torilarvensis Lotfollahi & Bahirai sp. nov. from Torilis arvensis (Huds.) Link (Apiaceae). They are the first eriophyoid mites collected on P. euphratica and T. arvensis respectively, and the later one is the first Aceria species found on plants of genus Torilis.

Prioritizing woody species for the rehabilitation of arid lands in western Iran based on soil properties and carbon sequestration

Plants are an important component in many natural ecosystems. They influence soil properties, especially in arid ecosystems. The selection of plant species based on their adaptations to site conditions is essential for rehabilitation of degraded sites and other construction sites such as check-dams. Other factors to be considered in species selection include their effects on soil properties and their abilities to meet other management objectives. The purpose of this study was to assess the effects of native (Populus euphratica Oliv. and Tamarix ramosissima Ledeb.) and introduced (Eucalyptus camaldulensis Dehnh. and Prosopis juliflora (Swartz) DC.) woody species on soil properties and carbon sequestration (CS) in an arid region of Iran. Soil sampling was collected at three soil depths (0–10, 10–20 and 20–30 cm) at the sites located under each woody species canopy and in an open area in 2017. Soil physical-chemical property was analyzed in the laboratory. The presence of a woody species changed soil characteristics and soil CS, compared with the open area. For example, the presence of a woody species caused a decrease in soil bulk density, of which the lowest value was observed under E. camaldulensis (1.38 g/cm3) compared with the open area (1.59 g/cm3). Also, all woody species significantly increased the contents of soil organic matter and total nitrogen, and introduced species had more significant effect than native species. The results showed that CS significantly increased under the canopy of all woody species in a decreasing order of P. euphratica (9.08 t/hm2)>E. camaldulensis (8.37 t/hm2)>P. juliflora (5.20 t/hm2)>T. ramosissima (2.93 t/hm2)>open area (1.33 t/hm2), thus demonstrating the positive effect of a woody species on CS. Although the plantation of non-native species had some positive effects on soil properties, we recommend increasing species diversity in plantations of native and introduced woody species to provide more diversity for the increased ecosystem services, resilience, health and long-term productivity.

Effect of the metallization treatment on the surface properties of Populus euphratica

Effect of the metallization treatment on the surface properties of Populus euphratica

UPLC-ESI-MS/MS and Various Chromatographic Technique for Identification of Phytochemicals in Populus euphratica Oliv. Leaves Extract

The aim of this study is to screen the phytochemicals found in Populus euphratica leaves since this type of trees are used traditionally by many villagers as treatment for eczema and other skin disease and also this plant is poorly investigated for their phytochemicals especially in Iraq. Phytochemical screening of the extracts obtained from the n-hexane and chloroform fraction of leaves of Populus euphratica was done by Thin-layer chromatography and various spraying reagents to test if alkaloids, sterols and other compounds are present. UPLC-electrospray ionization –tandem mass spectroscopy along with GC-MS and HPTLC are used to identify the phytochemicals present in the plant leaves.UPLC-ESI-MS/MS method 20 compounds have been identified in various fractions among which are protopine alkaloids. salicin, salicortin, tremulacin. GC-MS showed that the observed data obtained are matched with that in NIST library and confirmed the presence of Hexadecanoic acid trimethylsilyl ester in 43.80% beta-Sitosterol in 37.14% and Diisooctyl phthalate 11.46%.UPLC-ESI-MS/MS is a powerful method for the identification of compounds in mixture based on comparison of their molecular, weight retention time and MS/MS fragmentation. Protopine alkaloid is identified for the first time in Populus euphratica and genus Populus. GC-MS is a valuable method for both qualification and quantification of various phytochemicals that are volatile in nature
 Keywords: Populus euphratica, GC-MS, phytochemical, UPLC-ESI-MS/MS

Hollow-bearing characteristics of Populus euphratica in the lower reaches of Tarim River, China

We analzyed the hollow ratio of tree trunks, tree hole parameters, and its distribution characteristics among different DBH and tree height classes in a long-term monitoring plots of Populus euphratica forest at the Argan section in the lower reaches of Tarim River. The results showed that P. euphratica in the study area had a high hollow ratio, in that trees with hollowness accounted for 56% of the total individuals, with a absolute value of 159 tree·hm-2. The hollow ratio of P. euphratica showed significant difference among different DBH classes and tree height classes. The hollow ratio was positively correlated with DBH, and negatively correlated with tree height. The density of P. euphratica with hollowness was 560 ind·hm-2 and 2 ind·tree-1. Most of tree holes appeared on the tree trunk (57.1%) and mainly in the middle of the trunk (31.3%). The hole with a diameter of 5-15 cm accounted for the largest proportion (38.2%). The total number of tree holes, the number of tree holes per tree, and the diameter of holes were positively correlated with DBH and negatively correlated with tree height. The distribution of different tree hole types among different DBH classes and tree height classes was different, with inconsistent changing trends. The distribution of tree holes showed significant difference acorss orientations, with most of which mainly toward the west. The occurrence rate of tree hollow in P. euphratica desert riparian forest was more serious. The larger the DBH of poplar tree was, the more obvious the degree of hollow. Therefore, it is of great significance to strengthen the conservation of young poplar trees and to restore degraded desert riparian forests.

Nitrogen rather than streamflow regulates the growth of riparian trees

In arid and semiarid regions, riparian forests are crucial for maintaining ecological biodiversity and sustainability, and supporting social and economic development. For the typical arid and semiarid ecosystem, streamflow variability is thought to be the dominant factor influencing the vulnerability and evolution of the riparian forests, which often leads to the neglect of other potentially important factors such as nutrient availability and transport. Here, we measured annual stable nitrogen isotopes (δ15N) and nitrogen concentrations (N%) in the tree rings of Populus euphratica Oliv. (Euphrates poplar) over a 90 year period (1920–2012), collected from the lower researches of the inland Heihe River, northwestern China. Coupling with our previous dual-isotope (δ13C and δ18O) chronologies and estimated intrinsic water-use efficiency (iWUE), we examined the linkages between tree-ring δ15N and δ18O, iWUE, streamflow, and then explored the contributions of each to tree growth during the study period. Our results show that after 1975, a statistically significant correlation between tree-ring δ15N and river streamflow appears, indicating the river as a potential carrier of nitrogen from the upper and middle reaches to the lower research trees. In addition, the linkage between tree-ring δ15N and iWUE suggests substantial influence of carbon and nitrogen together on photosynthesis and transpiration of trees, although this connection become decoupled since AD 1986. The commonality analysis revealed that the nitrogen impacts indicated by tree-ring δ15N on tree growth cannot be ignored when evaluating riparian forest development. The fertilization effects caused by rising CO2 concentration complicate the nitrogen constraints on tree growth during the later part of the past century. Our results have potentially broad implications for identifying the limited factors for dryland forest ecosystems that are susceptible to natural water resource variations and human activities.

Distribution pattern of Tugai forests species diversity and their relationship to environmental factors in an arid area of China

Ecological restoration of degraded riparian Tugai forests is a key driver to combat desertification in arid regions. Previous studies have focused mainly on changes in groundwater as the underlying mechanisms of Tugai forest’s decline. We evaluated species composition and diversity of Tugai forest and their relationship to groundwater, soil salinity, and soil nutrient. Using 73 quadrats (100 m × 100 m) from 13 transects located perpendicularly to river in the upper reaches of the Tarim River. Eighteen plant species belonging to sixteen genera and eight families were recorded, and the dominant species included Populus euphratica, Phragmites communis, and Tamarix ramosissima. Three P. euphratica stand ages were detected: young stand, mature stand, and old stand. There were significant differences in species diversity, groundwater depth, groundwater salinity, distance from the quadrat to the river channel, soil moisture content, pH, electrical conductivity, total salt, Cl−, SO42−, Ca2−, Mg2+, Na+, K+, soil organic carbon, and soil organic matter across the stand ages. Seven species were identified as indicators of the three stand ages. Redundancy analysis indicated that the Tugai forest diversity indices were negatively correlated with groundwater depth, groundwater salinity, and distance from the river, and positively associated with electrical conductivity, total salt, pH, Cl−, SO42−, CO32−, soil organic matter, soil organic carbon, and soil moisture content. Plant diversity was the highest at 3–6 m groundwater depth, followed by 0–3 m and then 6–9 m, with the lowest recorded at > 9 m. The appropriate groundwater depth for herbs was about 1–4 m, whereas the depth for trees and shrubs was about 3–6 m. The groundwater depth < 6 m was deemed suitable for the growth of desert riparian forests. This results provide a scientific reference for the ecological restoration and protection for Tugai forests in arid areas.

Impact of groundwater depth and soil salinity on riparian plant diversity and distribution in an arid area of China

Riparian plant diversity in arid regions is sensitive to changes in groundwater. Although it is well known that groundwater has a significant influence on plant diversity, there have been few studies on how groundwater and soil salinity impact plant community in desert riparian ecosystems. Therefore, we surveyed 77 quadrats (100 m × 100 m) to examine the relationship between groundwater depth, groundwater salinity, soil salinity and plant community in the upper reaches of the Tarim River. Data were analyzed with two-way indicator species analysis (TWINSPAN), detrended canonical correspondence analysis (DCCA) and principal component analysis (PCA). The results indicated that Populus euphratica, Tamarix ramosissima, and Phragmites australis were the dominant plants among trees, shrubs and herbs, respectively. Five plant community types were classified. There were significant differences in species diversity, soil moisture, soil salinity, groundwater depth and groundwater salinity across the community types. The composition and distribution of plant community are significantly influenced by groundwater depth, groundwater salinity, soil moisture, distances from the river to the quadrats, soil pH, electrical conductivity, total salt, CO32−, Cl−, SO42−, Ca2+, Mg2+, Na+ and K+. Shallow groundwater depth, low groundwater salinity, and high soil moisture and soil salinity were associated with higher plant diversity.

PeSTZ1 confers salt stress tolerance by scavenging the accumulation of ROS through regulating the expression of PeZAT12 and PeAPX2 in Populus.

ZINC FINGER OF ARABIDOPSIS THALIANA12 (ZAT12) plays an important role in stress responses, but the transcriptional regulation of ZAT12 in response to abiotic stress remains unclear. In this study, we confirmed that a SALT TOLERANCE ZINC FINGER1 transcription factor from Populus euphratica (PeSTZ1) could regulate the expression of PeZAT12 by dual-luciferase reporter (DLR) assay and electrophoretic mobility shift assay. The expression of PeSTZ1 was rapidly induced by NaCl and hydrogen peroxide (H2O2) treatments. Overexpressing PeSTZ1 in poplar 84K (Populus alba × Populus glandulosa) plant was endowed with a strong tolerance to salt stress. Under salt stress, transgenic poplar exhibited higher expression levels of PeZAT12 and accumulated a larger amount of antioxidant than the wild-type plants. Meanwhile, ASCORBATE PEROXIDASE2 (PeAPX2) can be activated by PeZAT12 and PeSTZ1, promoting the accumulation of cytosolic ascorbate peroxidase (APX) to scavenge reactive oxygen species (ROS) under salt stress. This new regulatory model (PeSTZ1-PeZAT12-PeAPX2) was found in poplar, providing a new idea and insight for the interpretation of poplar resistance. Transgenic poplar reduced the accumulation of ROS, restrained the degradation of chlorophyll and guaranteed the photosynthesis and electron transport system. On the other hand, transgenic poplar slickly adjusted K+/Na+ homeostasis to alleviate salt toxicity in photosynthetic organs of plants under salt stress and then increased biomass accumulation. In summary, PeSTZ1 confers salt stress tolerance by scavenging the accumulation of ROS through regulating the expression of PeZAT12 and PeAPX2 in poplar.

Short-term transcriptomic responses of Populus euphratica roots and leaves to drought stress

Populus euphratica Oliv., the Euphrates poplar, is the tallest tree species in the arid desert areas of Northwest China. Investigation of its drought-resistance genes is valuable to increase understanding of drought resistance mechanisms. RNA-seq of leaves and roots under drought simulation by 25% polyethylene glycol-6000 (PEG 6000) were performed at 0, 4, and 12 h. Leaves and roots responded differently to drought via differentially upregulated and downregulated genes; more genes were downregulated than upregulated in both leaves and roots. Additionally, these differentially expressed genes were enriched in different GO terms and KEGG pathways. For example, GO term ‘response to organic substance’ and KEGG pathway ‘nitrogen metabolism’ were enriched for drought-stressed leaves, while GO term ‘cell wall organization or biogenesis’ and KEGG pathway ‘zeatin biosynthesis’ were enriched for drought-stressed roots. The enrichment of the GO term ‘enzyme linked receptor protein signalling pathway’ in both leaf and root drought responses suggests that these tissues may also have similar mechanisms. However, roots under drought stress for four hs responded by activating programed cell death. The KEGG pathway ‘plant hormone signal transduction’ was detected for 4- and 12-h drought-stressed leaves and 12-h drought-stressed roots, suggesting that plant hormone signal transduction plays an important role in both roots and leaves. GO enrichment of upregulated and downregulated genes for leaves and roots reflect differentially regulatory mechanisms of response to drought stress via different biological processes such as the regulation of photosynthesis and auxin signalling pathway in leaves, and the regulation of defence response and water homeostasis in roots. Fifteen candidate genes, including transcription factors, protein kinase, transporter, late embryogenesis abundant protein and mannitol dehydrogenase, were further selected to determine their response to drought using qRT-PCR. The results show that the expression patterns of 13 of the 15 genes correspond to the RNA-seq results. This study provides new insights into the drought response mechanism of P. euphratica and suggests new candidate gene resources.

Genome resequencing reveals demographic history and genetic architecture of seed salinity tolerance in Populus euphratica.

Populus euphratica is a dominant tree species in desert riparian forests and possesses extraordinary adaptation to salinity stress. Exploration of its genomic variation and molecular underpinning of salinity tolerance is important for elucidating population evolution and identifying stress-related genes. Here, we identify approximately 3.15 million single nucleotide polymorphisms using whole-genome resequencing. The natural populations of P. euphratica in northwest China are divided into four distinct clades that exhibit strong geographical distribution patterns. Pleistocene climatic fluctuations and tectonic deformation jointly shaped the extant genetic patterns. A seed germination rate-based salinity tolerance index was used to evaluate seed salinity tolerance of P. euphratica and a genome-wide association study was implemented. A total of 38 single nucleotide polymorphisms were associated with seed salinity tolerance and were located within or near 82 genes. Expression profiles showed that most of these genes were regulated under salt stress, revealing the genetic complexity of seed salinity tolerance. Furthermore, DEAD-box ATP-dependent RNA helicase 57 and one undescribed gene (CCG029559) were demonstrated to improve the seed salinity tolerance in transgenic Arabidopsis. These results provide new insights into the demographic history and genetic architecture of seed salinity tolerance in desert poplar.