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New genotypes of hybrid from the Aigeiros and Tacamahaca sections, which encompass economically important species of Populus L., have great potential to significantly enhance genetic gain from selection. Growth and its functional and structural determinants exhibiting a high level of variability are not only controlled by genetics, but also affected by environment, as well as genotype and environment interaction (G×E). The preceding research on the intersectional progenies derived from eight families ( P . simonii × P . nigra ) and their respective parents has indicated that leaf traits exhibiting robust genetic control were employed for selection of hybrid genotypes displaying multiple traits. The goals of this research with the progenies 3 families across two spacing trials were to (1) assess the GEI in progeny genotypes for multiple traits, (2) estimate the genetic parameters for important traits, (3) identify the genotypes with superior productive performance, adaptability, and genotypic stability using the MGIDI index, (4) select genotypes that exhibit high performance and genotypic stability across multiple traits using the MGIDI index. We found that the progeny genotypes showed considerable variation in growth and leaf morphology response to the spacings and genotype interaction effects were significant (P ≤ 0.001) for most of the traits studied in the progeny of each family and the joint family. The highest broad-sense heritability was observed for petiole length, while the lowest heritability values were recorded for stomatal length among the eight traits studied in both each family and the joint family. The MGIDI, assuming selection intensity of 15%, identified 26, 25, 35, and 86 genotypes in the three families and the joint family, respectively. The selected hybrids of each family and the joint family exhibited the desired genetic gains, including positive gains for leaf area (6.87%-11.2%), petiole length (3.81%-13.7%) and plant height (1.30%-10.4%). The interpretation of strengths and weaknesses as illustrated by the MGIDI provides guidance for the breeders to develop poplar hybrids performed well in desired traits, such as growth and other yield contributors i.e. leaf traits. The tested progeny genotypes of three families provided a valuable addition to the hybrid selection for rapid juvenile growth.

Background Breeding drought-tolerant poplar cultivars necessitates efficient selection strategies that can simultaneously improve multiple traits. This study evaluated the integration of multivariate selection indices with Weighted Rank Aggregation (WRA) to identify superior genotypes in hybrid poplar progenies. Methods We assessed 372 F 1 progenies from three families of Populus simonii × P. nigra under controlled drought stress and well-watered conditions. Data on 16 growth, leaf, and photosynthetic traits were analyzed using four multivariate indices: the Smith-Hazel Index (SHI), FAI-BLUP, and two Multi-Trait Genotype-Ideal Genotype Distance Index (MGIDI) variants. The rankings were integrated using WRA. Results Genetic parameters revealed high heritability for key growth traits. The selection indices exhibited divergent focus, with SHI showing strong directional selection for growth but sensitivity to multicollinearity, while FAI-BLUP and MGIDI enabled more balanced multi-trait improvements. Most indices were weakly correlated (Spearman’s |r| < 0.2), indicating complementary information. Venn analysis identified genotypes (e.g., C4‑246, E4‑70) performing consistently across multiple indices. The final WRA integration selected robust genotypes, including C2‑65, C4‑210, E4‑115, and E4‑70, which combine drought tolerance with desirable growth and physiological characteristics. Conclusions Integrating multiple selection indices with WRA provides a powerful and reliable strategy for selecting drought-tolerant poplar genotypes at the seedling stage. This approach effectively balances genetic gains across traits, enhancing the efficiency of breeding programs for stress resilience.

The screening of poplar varieties that demonstrate tolerance to low nitrogen (N) represents a promising strategy for improving nitrogen-use efficiency in trees. Such an approach could reduce reliance on N fertilizers while mitigating environmental pollution associated with their cultivation. In this study, a total of 87 poplar varieties were evaluated in a controlled greenhouse pot experiment. Under both low-nitrogen (LN) and normal-nitrogen (NN) conditions, 18 traits spanning four categories—growth performance, leaf morphology, chlorophyll fluorescence, and N isotope parameters were measured. For 13 of these traits (growth, leaf morphology, chlorophyll fluorescence), genetic variation and parameters, including genotypic values, were analyzed using best linear unbiased prediction (BLUP) within a linear mixed model (LMM). LN tolerance of tested poplar varieties was comprehensively assessed with three MGIDI strategies by integrating means, BLUPs, and low-nitrogen tolerance coefficient (LNindex) to rank poplar varieties. The results exhibited highly significant differences across all traits between LN and NN experiments, as well as among varieties. LN stress markedly inhibited growth, altered leaf morphology, and reduced chlorophyll fluorescence parameters in young poplar plants. Among the selection strategies, the MGIDI_LNindex approach demonstrated the highest selection differential percent (SD% = 10.5–35.23%). Using a selection intensity (SI) of 20%, we systematically identified 17 superior genotypes across all three strategies. In a thorough, comprehensive MGIDI-based evaluation, these varieties exhibited exceptional adaptability and stability under LN stress. The selected genotypes represent valuable genetic resources for developing improved poplar cultivars with enhanced low-nitrogen tolerance.

Background Nitrogen (N) is one of the main factors limiting the wood yield in poplar cultivation. Understanding the molecular mechanism of N utilization could play a guiding role in improving the nitrogen use efficiency (NUE) of poplar. Results In this study, three N-efficient genotypes (A1-A3) and three N-inefficient genotypes (C1-C3) of Populus deltoides were cultured under low N stress (5 μM NH 4 NO 3 ) and normal N supply (750 μM NH 4 NO 3 ). The dry matter mass, leaf morphology, and chlorophyll content of both genotypes decreased under N starvation. The low nitrogen adaptation coefficients of the leaves and stems biomass of group A were significantly higher than those of group C ( p  < 0.05). Interestingly, N starvation induced fine root growth in group A, but not in group C. Next, a detailed time-course analysis of enzyme activities and gene expression in leaves identified 2062 specifically differentially expressed genes (DEGs) in group A and 1118 in group C. Moreover, the sensitivity to N starvation of group A was weak, and DEGs related to hormone signal transduction and stimulus response played an important role in the low N response this group. Weighted gene co-expression network analysis identified genes related to membranes, catalytic activity, enzymatic activity, and response to stresses that might be critical for poplar’s adaption to N starvation and these genes participated in the negative regulation of various biological processes. Finally, ten influential hub genes and twelve transcription factors were identified in the response to N starvation. Among them, four hub genes were related to programmed cell death and the defense response, and PodelWRKY18 , with high connectivity, was involved in plant signal transduction. The expression of hub genes increased gradually with the extension of low N stress time, and the expression changes in group A were more obvious than those in group C. Conclusions Under N starvation, group A showed stronger adaptability and better NUE than group C in terms of morphology and physiology. The discovery of hub genes and transcription factors might provide new information for the analysis of the molecular mechanism of NUE and its improvement in poplar.

In comparison to conventional rTMS, theta burst stimulation is stronger and more effective as a brain stimulation approach within short periods of time. Although this deep rTMS technique is being applied in treating neuropsychiatric disorders, few animal studies have attempted to clarify the neurobiological mechanisms underlying its beneficial effects. This animal study examined effects of deep rTMS on the cuprizone-induced neuropathologic and behavioral anomalies and explored the underlying mechanism. Adolescent male C57BL/6 mice were fed a rodent chow without or with cuprizone (CPZ; 0.2% w/w) for 5 weeks. Another two groups of mice were subjected to deep rTMS or sham rTMS once a day during weeks 2-5 of the CPZ-feeding period. The behaviors of all mice were assessed after withdrawal of CPZ prior to neuropathological and immunological analyses. Compared to CNT group, mice in CPZ and CPZ+Sham groups showed deficits in social recognition and spatial working memory as well as anxiety-like behavior, in addition to myelin breakdown and OL loss in corpus callosum, caudate putamen, cerebral cortex, and hippocampus of the brain. Deep rTMS effectively reduced behavioral anomalies and blocked myelin breakdown and OL loss in CPZ-fed mice. In addition, it also dampened microglia activation at lesion sites and rectified cytokines levels (IL-1β, IL-6, and IL-10) in CPZ-affected regions. The most significant effect was seen in cerebral cortex where alleviated neuropathology co-existed with less microglia activation and higher IL-10 level. These data provided experimental evidence for the beneficial effects of deep rTMS in CPZ-fed mice and revealed a neurobiological mechanism of the modality.

Plants growing in natural environments are constantly exposed to various biotic and abiotic stresses, among which drought is a major abiotic factor that severely limits growth and development. As a water-demanding species, Populus is particularly vulnerable to drought under the context of global climate warming, making its drought tolerance a key determinant of adaptability and productivity. R2R3-MYB transcription factors play critical regulatory roles in plant responses to drought stress. In this study, we performed a comprehensive genome-wide identification and analysis of the R2R3-MYB gene family in P. deltoides ‘I-69’ using bioinformatics approaches, and further investigated the drought-responsive function of PdMYB2R032 through transgenic experiments. A total of 100 R2R3-MYB genes ( Pd2RMYBs ) were identified and classified into 12 subgroups based on phylogenetic analysis. Cis -element analysis of promoter regions revealed abundant motifs related to light response, hormone signaling, and drought regulation. Gene Ontology (GO) annotation indicated that Pd2RMYBs are potentially involved in hormone signaling pathways and responses to abiotic stresses. Phylogenetic analysis showed that PdMYB2R032 from P. deltoides × P. euramericana ‘Nanlin895’ is most closely related to Pd2RMYB21 in P. deltoides ‘I-69’. Functional studies revealed that overexpression of PdMYB2R032 in Arabidopsis thaliana significantly promoted root development and biomass accumulation under drought conditions. In addition, PdMYB2R032 regulated stomatal movement by reducing stomatal aperture under drought stress, thereby minimizing water loss. It also reduced malondialdehyde (MDA) accumulation, alleviating drought-induced oxidative damage. Furthermore, PdMYB2R032 enhanced seed germination in transgenic Arabidopsis . Collectively, these results demonstrate that PdMYB2R032 acts as a positive regulator of drought tolerance through multiple biological pathways, providing theoretical support for elucidating the drought-responsive mechanisms of R2R3-MYB genes and for molecular breeding of drought-resistant poplars.

Flooding, as a major abiotic stress, significantly impacts the growth and survival of poplar plantations in the floodplains of the middle and lower reaches of the Yangtze River. Elucidating the molecular mechanisms underlying flooding responses in poplar is crucial for enhancing plantation productivity. In this study, two important eastern cottonwood cultivars, Populus deltoides ‘Jianghan 1’ (HBI) and P. deltoides Bartr. CL (CL), were investigated. By integrating long-term growth surveys and transcriptome sequencing, we analyzed their phenotypic traits and molecular responses to flooding stress. After 7 years of seasonal flooding, HBI exhibited a survival rate of 73.91%, along with superior height (23.1 m) and diameter at breast height (DBH, 26.3 cm), compared with CL, indicating HBI as a flooding-tolerant cultivar. Transcriptome analysis identified 1098 shared differentially expressed genes (DEGs) in the leaves of flooded HBI and CL, which were mainly enriched in stress signal perception, oxidative stress regulation, energy metabolism and circadian rhythm. Cultivar-specific DEG analysis revealed that CL mainly activated pathways related to oxidative stress and damage repair pathways, whereas HBI-specific genes were significantly enriched in hormone signal transduction, growth regulation, flavonoid synthesis and photosynthesis. Based on this distinct enrichment pattern in the tolerant cultivar HBI, we propose that it possesses adaptive advantages under flooding stress. Specifically, HBI likely coordinates multiple physiological processes by activating ethylene and other hormone-related genes, thereby regulating hypoxia adaptation, reoxygenation-induced oxidative stress, photosynthetic recovery, and flavonoid-mediated antioxidant defense. This coordinated regulation collectively sustains growth vigor and enhances survival under seasonal inundation. Our findings demonstrate clear transcriptomic divergence underlying flooding tolerance among poplar cultivars, laying a theoretical foundation for the selection of flooding-tolerant varieties and the sustainable development of forestry in flood-prone regions. Furthermore, these results broaden the current knowledge of flooding stress biology in woody plants.

Salt stress is one of the main factors that affect both growth and development of plants. Maintaining K+/Na+ balance in the cytoplasm is important for metabolism as well as salt resistance in plants. In the present study, we monitored the growth (height and diameter) of transgenic Populus alba × P. berolinensis trees (ABJ01) carrying JERF36s gene (a tomato jasmonic/ethylene responsive factors gene) over 4 years, which showed faster growth and significant salt tolerance compared with non-transgenic poplar trees (9#). The expression of NHX1 and SOS1 genes that encode Na+/H+ antiporters in the vacuole and plasma membranes was measured in leaves under NaCl stress. Non-invasive micro-test techniques (NMT) were used to analyse ion flux of Na+, K+, and H+ in the root tip of seedlings under treatment with100 mM NaCl for 7, 15, and 30 days. Results showed that the expression of NHX1 and SOS1 was much higher in ABJ01 compared with 9#, and the Na+ efflux and H+ influx fluxes of root were remarkable higher in ABJ01 than in 9#, but K+ efflux exhibited lower level. All above suggest that salt stress induces NHX1 and SOS1 to a greater expression level in ABJ01, resulting in the accumulation of Na+/H+ antiporter to better maintain K+/Na+ balance in the cytoplasm of this enhanced salt resistant variety. This may help us to better understand the mechanism of transgenic poplars with improving salt tolerance by overexpressing JERF36s and could provide a basis for future breeding programs aimed at improving salt resistance in transgenic poplar.

Certain plant genotypes can achieve optimal growth under appropriate environmental conditions. Under high planting density conditions, plants undergo competition for uptake and utilization of light and nutrients. However, the relationship between whole-genome expression patterns and the planting density in perennial woody plants remains unknown. In this study, whole-genome RNA sequencing of poplar (Populus × euramericana) was carried out at three different sampling heights to determine gene expression patterns under high (HD) and low (LD) planting densities. As a result, 4,004 differentially expressed genes (DEGs) were detected between HD and LD, of which 2,300, 701, and 1,003 were detected at the three positions, upper, middle and bottom, respectively. Function annotation results further revealed that a large number of the DEGs were involved in distinct biological functions. There were significant changes in the expression of metabolism-related and stimulus-related genes in response to planting density. There were 37 DEGs that were found at all three positions and were subsequently screened. Several DEGs related to plant light responses and photosynthesis were observed at different positions. Meanwhile, numbers of genes related to auxin/indole-3-acetic acid, and carbon and nitrogen metabolism were also revealed, displaying overall trends of upregulation under HD. These findings provide a basis for identifying candidate genes related to planting density and could increase our molecular understanding of the effect of planting density on gene expression.

It is important to evaluate nitrogen use efficiency and nitrogen tolerance of trees in order to improve their productivity. In this study, both were evaluated for 338 Populus deltoides genotypes from six provenances. The plants were cultured under normal nitrogen (750 μM NH 4 NO 3 ) and low nitrogen (5 μM NH 4 NO 3 ) conditions for 3 months. Growth, chlorophyll content and glutamine synthetase activity of each genotype were measured. Under low nitrogen, heights, ground diameter, leaf area, leaf and root biomass, and chlorophyll contents were significantly lower than those under normal nitrogen level. Correlation analysis showed that nutrient distribution changed under different nitrogen treatments. There was a negative correlation between leaf traits and root biomass under normal nitrogen level, however, the correlation became positive in low nitrogen treatment. Moreover, with the decrease of nitrogen level, the negative correlation between leaf morphology and chlorophyll levels became weakened. The growth of the genotypes under the two treatments was evaluated by combining principal component analysis with a fuzzy mathematical membership function; the results showed that leaf traits accounted for a large proportion of the variation in the evaluation model. According to the results of comprehensive evaluation of plants under the two treatments, the 338 P. deltoides genotypes could be divided into nine categories, with wide genotypic diversity in nitrogen use efficiency and low nitrogen tolerance. As a result, 26 N-efficient genotypes and 24 N-inefficient genotypes were selected. By comparative analysis of their morphological and physiological traits under the two treatments, leaf traits could be significant indicators for nitrogen use efficiency and nitrogen tolerance, which is of considerable significance for breeding poplar varieties with high nitrogen use efficiencies.