Differences in carbon and nitrogen metabolism between male and female Populus cathayana in response to deficient nitrogen

Divergence of rhizosphere microbial communities between females and males of the dioecious Hippophae tibetana at different habitats

Females and males of dioecious plants have evolved sex-specific characteristics in terms of their morphological and physiological properties. However, little is known about the difference in rhizosphere microbes in dioecious plants. In this study, we used amplicon sequencing to analyze the differences in rhizosphere microbial diversity and community composition of males and females of dioecious Hippophae tibetana at different habitats, and their key factors in driving the differences were investigated. The results showed that there were differences in the diversity, community composition, and connectivity and complexity of the co-occurrence network of rhizosphere microbes between females and males of the dioecious H. tibetana at different habitats. Zoopagomycota is a unique phylum of rhizosphere fungi in the males of the dioecious H. tibetana, while Dependentiae is a unique phylum of rhizosphere bacteria in the females of the dioecious H. tibetana. Linear discriminant analysis effect size (LEfSe) analysis indicated significant enrichment of species at different levels, suggesting that these species could be potential biomarkers for females and males of H. tibetana. Spearman's analysis showed that the dominant genera of rhizosphere fungi were significantly positively correlated with soil physicochemical properties (total nitrogen and phosphorus; organic matter; available phosphorus, potassium and nitrogen; salt content; water content). PICRUSt and FUNGuild predictive analysis indicated that the function of rhizosphere fungi was different between females and males of the dioecious H. tibetana at different habitats, while metabolites were the dominant functions of rhizosphere bacteria in all samples. These results highlighted the sexual discrimination of rhizosphere microbes on the dioecious plants and provided important knowledge for females and males of the dioecious plant-microbe interaction.IMPORTANCEThis study explores the differences in rhizosphere microbes of dioecious Hippophae tibetana at different habitats and their key factors in driving the differences. Through employing amplicon sequencing techniques, we found that rhizosphere microbial communities and diversity were different between females and males of the dioecious H. tibetana at different habitats, and there notably existed unique phylum and potential biomarkers of rhizosphere microbes between females and males of the dioecious H. tibetana. Rhizosphere fungi were significantly positively correlated with soil physicochemical properties. This study reveals the differences in rhizosphere microbes of dioecious H. tibetana at different habitats and driving factors; it also contributes to our understanding of the dioecious plant-microbe interaction.

Sex-specific responses of Taxus mairei to UV-B radiation involved altering the interactions between the microbiota assembly and host secondary metabolism

BACKGROUND

To adapt to constantly changing environments, ancient gymnosperms have coevolved with diverse endophytic fungi that are essential for the fitness and adaptability of the plant host. However, the effect of sex on plant-endophyte interactions in response to environmental stressors remains unknown. RNA-seq integrated with ITS analysis was applied to reveal the potential mechanisms underlying the sex-specific responses of Taxus mairei to ultraviolet (UV)-B radiation.

RESULTS

Enrichment analysis suggested that sex influenced the expression of several genes related to the oxidation-reduction system, which might play potential roles in sex-mediated responses to UV-B radiations. ITS-seq analysis clarified the effects of UV-B radiation and sex on the composition of endophytic fungal communities. Sex influenced various secondary metabolic pathways, thereby providing chemicals for T. mairei host to produce attractants and/or inhibitors to filter microbial taxa. Analysis of fungal biomarkers suggested that UV-B radiation reduced the effect of sex on fungal communities. Moreover, Guignardia isolate #1 was purified to investigate the role of endophytic fungi in sex-mediated responses to UV-B radiation. Inoculation with spores produced by isolate #1 significantly altered various oxidation-reduction systems of the host by regulating the expression of APX2, GST7 NCED1, ZE1, CS1, and CM1.

CONCLUSION

These results revealed the roles of endophytic fungi in sex-mediated responses to UV-B radiation and provided novel insights into the sex-specific responses of Taxus trees to environmental stressors. Video Abstract.

Metabolomics analysis of different diameter classes of Taxus chinensis reveals that the resource allocation is related to carbon and nitrogen metabolism

Taxus chinensis (Taxus cuspidata Sieb. et Zucc.) is a traditional medicinal plant known for its anticancer substance paclitaxel, and its growth age is also an important factor affecting its medicinal value. However, how age affects the physiological and metabolic characteristics and active substances of T. chinensis is still unclear. In this study, carbon and nitrogen accumulation, contents of active substances and changes in primary metabolites in barks and annual leaves of T. chinensis of different diameter classes were investigated by using diameter classes instead of age. The results showed that leaves and barks of small diameter class (D1) had higher content of non-structural carbohydrates and C, which were effective in enhancing defense capacity, while N content was higher in medium (D2) and large diameter classes (D3). Active substances such as paclitaxel, baccatin III and cephalomannine also accumulated significantly in barks of large diameter classes. Moreover, 21 and 25 differential metabolites were identified in leaves and barks of different diameter classes, respectively. The differential metabolites were enhanced the TCA cycle and amino acid biosynthesis, accumulate metabolites such as organic acids, and promote the synthesis and accumulation of active substances such as paclitaxel in the medium and large diameter classes. These results revealed the carbon and nitrogen allocation mechanism of different diameter classes of T. chinensis, and its relationship with medicinal components, providing a guidance for the harvesting and utilization of wild T. chinensis.

Drought Stress Might Induce Sexual Spatial Segregation in Dioecious Populus euphratica-Insights from Long-Term Water Use Efficiency and Growth Rates

P. euphratica stands as the pioneering and dominant tree within desert riparian forests in arid and semi-arid regions. The aim of our work was to reveal why dioecious P. euphratica in natural desert riparian forests in the lower Tarim River exhibits sexual spatial distribution differences combined with field investigation, tree ring techniques, isotope analysis techniques, and statistical analyses. The results showed that P. euphratica was a male-biased population, with the operational sex ratio (OSR) exhibiting spatial distribution differences to variations in drought stress resulting from groundwater depth change. The highest OSR was observed under mild drought stress (groundwater depth of 6-7 m), and it was reduced under non-drought stress (groundwater depth below 6 m) or severe drought stress (groundwater depth exceeding 7 m). As drought stress escalated, the degradation and aging of the P. euphratica forest became more pronounced. Males exhibited significantly higher growth rates and WUEi than females under mild drought stress. However, under severe drought stress, males' growth rates significantly slowed down, accompanied by significantly lower WUEi than in females. This divergence determined the sexual spatial segregation of P. euphratica in the natural desert riparian forests of the lower Tarim River. Furthermore, the current ecological water conveyance project (EWCP) in the lower Tarim River was hard to fundamentally reverse the degradation and aging of the P. euphratica forest due to inadequate population regeneration. Consequently, we advocated for an optimized ecological water conveyance mode to restore, conserve, and rejuvenate natural P. euphratica forests.

Interspecific plant interaction structures the microbiomes of poplar-soil interface to alter nutrient cycling and utilization

Terrestrial plants can influence the growth and health of adjacent plants through interspecific interaction. Here, the mechanisms of interspecific plant interaction on microbial function and nutrient utilization in the plant-soil interface (non-rhizosphere soil, rhizosphere soil, and root) were studied by soybean- and potato-poplar intercropping. First, metagenomics showed that soybean- and potato-poplar intercropping influenced the composition and co-occurrence networks of microbial communities in different ecological niches, with higher stability of the microbial community in soybean intercropping. Second, the gene abundance related to carbon metabolism, nitrogen cycling, phosphorus cycling, and sulfur cycling was increased at the poplar-soil interface in soybean intercropping. Moreover, soybean intercropping increased soil nutrient content and enzymatic activity. It showed higher metabolic potential in nutrient metabolism and transportation. Third, functional microorganisms that influenced nutrient cycling and transportation in different intercropping have been identified, namely Acidobacteria, Sphingomonas, Gemmatimonadaceae, Alphaproteobacteria, and Bradyrhizobium. Therefore, intercropping can construct microbial communities to alter metabolic functions and improve nutrient cycling and absorption. Interspecific plant interactions to influence the microbiome were revealed, opening up a new way for the precise regulation of plant microbiome.IMPORTANCEPoplar has the characteristics of wide distribution, strong adaptability, and fast growth, which is an ideal tree species for timber forest. In this study, metagenomics and elemental analysis were used to comprehensively reveal the effects of interspecific plant interactions on microbial communities and functions in different ecological niches. It can provide a theoretical basis for the development and application of the precise management model in poplar.

Male, female, and mixed-sex poplar plantations support divergent soil microbial communities

Males and females of dioecious plants have sex-specific adaptations to diverse habitats. The effects of inter- and intrasexual interactions in poplar plantations on composition, structure, and function of soil microbiota have not been explored in degraded areas. We conducted a series of greenhouse and field experiments to investigate how belowground competition, soil microbial communities, and seasonal variation nitrogen content differ among female, male, and mixed-sex Populus cathayana plantations. In the greenhouse experiment, female neighbors suppressed the growth of males under optimal nitrogen conditions. However, male neighbors enhanced stable isotope ratio of nitrogen (δ15 N) of females under intersexual competition. In the field, the root length density, root area density, and biomass of fine roots were lower in female plantations than in male or mixed-sex plantations. Bacterial networks of female, male, and mixed-sex plantations were characterized by different composition of hub nodes, including connectors, modules, and network hubs. The sex composition of plantations altered bacterial and fungal community structures according to Bray-Curtis distances, with 44% and 65% of variance explained by the root biomass, respectively. The total soil nitrogen content of mixed-sex plantation was higher than that in female plantation in spring and summer. The mixed-sex plantation also had a higher β-1,4-N-acetyl-glucosaminidase activity in summer and a higher nitrification rate in autumn than the other two plantations. The seasonal soil N content, nitrification rate, and root distribution traits demonstrated spatiotemporal niche separation in the mixed-sex plantation. We argue that a strong female-female competition and limited nitrogen content could strongly impede plant growth and reduce the resistance of monosex plantations to climate change and the mixed-sex plantations constitutes a promising way to restore degraded land.

How does plant sex alter microbiota assembly in dioecious plants?

Plant microbiota can greatly impact plant growth, defense, and health in different environments. Thus, it might be evolutionarily beneficial for plants to be able to control processes related to microbiota assembly. Dioecious plant species display sexual dimorphism in morphology, physiology, and immunity. These differences imply that male and female individuals might differently regulate their microbiota, but the role of sex in microbiota assembly has been largely neglected so far. Here, we introduce the mechanism of how sex controls microbiota in plants analogically to the sex regulation of gut microbiota in animals, in particular in humans. We argue that plant sex imposes selective pressure on filtering and constructing microbiota in the rhizosphere, phyllosphere, and endosphere along the soil-plant continuum. Since male plants are more resistant than female plants to environmental stresses, we suggest that a male host forms more stable and resistant plant microbiota that cooperate more effectively with the host to resist stresses. Male and female plants can distinguish whether a plant is of the same or different sex, and males can alleviate stress-caused damage in females. The impact of a male host on microbiota would protect female plants from unfavorable environments.

Combining GS-assisted GWAS and transcriptome analysis to mine candidate genes for nitrogen utilization efficiency in Populus cathayana

BACKGROUND

Forest trees such as poplar, shrub willow, et al. are essential natural resources for sustainable and renewable energy production, and their wood can reduce dependence on fossil fuels and reduce environmental pollution. However, the productivity of forest trees is often limited by the availability of nitrogen (N), improving nitrogen use efficiency (NUE) is an important way to address it. Currently, NUE genetic resources are scarce in forest tree research, and more genetic resources are urgently needed.

RESULTS

Here, we performed genome-wide association studies (GWAS) using the mixed linear model (MLM) to identify genetic loci regulating growth traits in Populus cathayana at two N levels, and attempted to enhance the signal strength of single nucleotide polymorphism (SNP) detection by performing genome selection (GS) assistance GWAS. The results of the two GWAS analyses identified 55 and 40 SNPs that were respectively associated with plant height (PH) and ground diameter (GD), and 92 and 69 candidate genes, including 30 overlapping genes. The prediction accuracy of the GS model (rrBLUP) for phenotype exceeds 0.9. Transcriptome analysis of 13 genotypes under two N levels showed that genes related to carbon and N metabolism, amino acid metabolism, energy metabolism, and signal transduction were differentially expressed in the xylem of P. cathayana under N treatment. Furthermore, we observed strong regional patterns in gene expression levels of P. cathayana, with significant differences between different regions. Among them, P. cathayana in Longquan region exhibited the highest response to N. Finally, through weighted gene co-expression network analysis (WGCNA), we identified a module closely related to the N metabolic process and eight hub genes.

CONCLUSIONS

Integrating the GWAS, RNA-seq and WGCNA data, we ultimately identified four key regulatory genes (PtrNAC123, PtrNAC025, Potri.002G233100, and Potri.006G236200) involved in the wood formation process, and they may affect P. cathayana growth and wood formation by regulating nitrogen metabolism. This study will provide strong evidence for N regulation mechanisms, and reliable genetic resources for growth and NUE genetic improvement in poplar.

Molecular responses to salinity stress in Salix matsudana (Koidz) females and males

Sexual dimorphism has commonly been found in many species. The phenotypes of Salix matsudana females and males are different under salinity stress. An F₁ population was selected to compare the differences between males and females. As a result, males showed stronger roots and heavier dry weights than females. The unique molecular mechanisms of males and females under salinity stress were further analyzed based on the root transcriptome of males and females. Both males and females up-regulated systemic acquired resistance genes, such as ADH and oxygenase-related genes, to resist salt. Moreover, many other abiotic stress response genes were up-regulated in males to adjust to salinity stress, while females showed more down-regulation of nitrogen metabolism-related genes to decrease the harm from salinity stress. The research on salinity tolerance in Salix matsudana males and females would help to further understand sexual dimorphism under selection pressure and provide benefits to the ecological environment.

Populus root exudates are associated with rhizosphere microbial communities and symbiotic patterns

Introduction

Microbial communities in the plant rhizosphere are critical for nutrient cycling and ecosystem stability. However, how root exudates and soil physicochemical characteristics affect microbial community composition in Populus rhizosphere is not well understood.

Methods

This study measured soil physiochemistry properties and root exudates in a representative forest consists of four Populus species. The composition of rhizosphere bacterial and fungal communities was determined by metabolomics and high-throughput sequencing.

Results

Luvangetin, salicylic acid, gentisic acid, oleuropein, strigol, chrysin, and linoleic acid were the differential root exudates extracted in the rhizosphere of four Populus species, which explained 48.40, 82.80, 48.73, and 59.64% of the variance for the dominant and key bacterial or fungal communities, respectively. Data showed that differential root exudates were the main drivers of the changes in the rhizosphere microbial communities. Nitrosospira, Microvirga, Trichoderma, Cortinarius, and Beauveria were the keystone taxa in the rhizosphere microbial communities, and are thus important for maintaining a stable Populus microbial rhizosphere. The differential root exudates had strong impact on key bacteria than dominant bacteria, key fungi, and dominant fungi. Moreover, strigol had positively effects with bacteria, whereas phenolic compounds and chrysin were negatively correlated with rhizosphere microorganisms. The assembly process of the community structure (keystone taxa and bacterial dominant taxa) was mostly determined by stochastic processes.

Discussion

This study showed the association of rhizosphere microorganisms (dominant and keystone taxa) with differential root exudates in the rhizosphere of Populus plants, and revealed the assembly process of the dominant and keystone taxa. It provides a theoretical basis for the identification and utilization of beneficial microorganisms in Populus rhizosphere.

Plant sex affects plant-microbiome assemblies of dioecious Populus cathayana trees under different soil nitrogen conditions

BACKGROUND

Dioecious plants have coevolved with diverse plant microbiomes, which are crucial for the fitness and productivity of their host. Sexual dimorphism in morphology, physiology, or gene expression may relate to different microbial compositions that affect male and female fitness in different environments. However, sex-specific impacts on ecological processes that control the microbiome assembly are not well known. In this study, Populus cathayana males and females were planted in different nitrogen conditions. It was hypothesized that males and females differently affect bacterial and fungal communities in the rhizosphere soil, roots, old leaves, and young leaves. Physiological traits and transcriptome profiles of male and female plants were investigated to reveal potential mechanisms that control the microbiome assembly.

RESULTS

Our results showed strong niche differentiation that shapes microbial communities leading to a rapid loss of diversity along a decreasing pH gradient from the rhizosphere soil to leaves. Sex had different impacts on the microbial assembly in each niche. Especially fungal endophytes showed great differences in the community structure, keystone species, and community complexity between P. cathayana males and females. For example, the fungal co-occurrence network was more complex and the alpha diversity was significantly higher in young female leaves compared to young male leaves. Transcriptome profiles revealed substantial differences in plant-pathogen interactions and physiological traits that clearly demonstrated divergent internal environments for endophytes inhabiting males and females. Starch and pH of young leaves significantly affected the abundance of Proteobacteria, while tannin and pH of roots showed significant effects on the abundance of Chloroflexi, Actinobacteria, and Proteobacteria, and on the bacterial Shannon diversity.

CONCLUSION

Our results provided important knowledge for understanding sexual dimorphism that affects microbial assemblies, thus advancing our understanding of plant-microbiome interactions. Video Abstract.

Integrated transcriptome and plant growth substance profiles to identify the regulatory factors involved in floral sex differentiation in Zanthoxylum armatum DC

Zanthoxylum armatum is a prominent plant for food industries. Its male flowers often occur in gynogenesis plants; however, the potential mechanism remains poorly understood. Herein, a total of 26 floral sex differentiation stages were observed to select four vital phases to reveal key factors by using RNA-seq, phytohormones and carbohydrates investigation. The results showed that a selective abortion of stamen or pistil primordia could result in the floral sex differentiation in Z. armatum. Carbohydrates might collaborate with cytokinin to effect the male floral differentiation, whereas female floral differentiation was involved in SA, GA₁, and ABA biosynthesis and signal transduction pathways. Meanwhile, these endogenous regulators associated with reproductive growth might be integrated into ABCDE model to regulate the floral organ differentiation in Z. armatum. Furthermore, the 21 crucial candidates were identified in co-expression network, which would contribute to uncovering their roles in floral sex differentiation of Z. armatum in further studies. To the best of our knowledge, this study was the first comprehensive investigation to link floral sex differentiation with multi-level endogenous regulatory factors in Z. armatum. It also provided new insights to explore the regulatory mechanism of floral sex differentiation, which would be benefited to cultivate high-yield varieties in Z. armatum.

The transcription factor GNC optimizes nitrogen use efficiency and growth by up-regulating the expression of nitrate uptake and assimilation genes in poplar

Plants have evolved complex mechanisms to cope with the fluctuating environmental availability of nitrogen. However, potential genes modulating plant responses to nitrate are yet to be characterized. Here, a poplar GATA transcription factor gene PdGNC (GATA nitrate-inducible carbon-metabolism-involved) was found to be strongly induced by low nitrate. Overexpressing PdGNC in poplar clone 717-1B4 (P. tremula × alba) significantly improved nitrate uptake, remobilization, and assimilation with higher nitrogen use efficiency (NUE) and faster growth, particularly under low nitrate conditions. Conversely, CRISPR/Cas9-mediated poplar mutant gnc exhibited decreased nitrate uptake, relocation, and assimilation, combined with lower NUE and slower growth. Assays with yeast one-hybrid, electrophoretic mobility shift, and a dual-luciferase reporter showed that PdGNC directly activated the promoters of nitrogen pathway genes PdNRT2.4b, PdNR, PdNiR, and PdGS2, leading to a significant increase in nitrate utilization in poplar. As expected, the enhanced NUE promoted growth under low nitrate availability. Taken together, our data show that PdGNC plays an important role in the regulation of NUE and growth in poplar by improving nitrate acquisition, remobilization, and assimilation, and provide a promising strategy for molecular breeding to improve productivity under nitrogen limitation in trees.

Integrated DNA methylation, transcriptome and physiological analyses reveal new insights into superiority of poplars formed by interspecific grafting

Plant grafting has a long history and it is extensively employed to improve plant performance. In our previous research, reciprocal grafts of Populus cathayana Rehder (C) and Populus deltoides Bart. Ex Marsh (D) were generated. The results showed that interspecific grafting combinations (scion/rootstock: C/D and D/C) grew better than intraspecific grafting combinations (C/C and D/D). To further understand differences in molecular mechanisms between interspecific and intraspecific grafting, we performed an integrated analysis, including bisulfite sequencing, RNA sequencing and measurements of physiological indicators, to investigate leaves of different grafting combinations. We found that the difference at the genome-wide methylation level was greater in D/C vs D/D than in C/D vs C/C, but no difference was detected at the transcription level in D/C vs D/D. Furthermore, the grafting superiority of D/C vs D/D was not as strong as that of C/D vs C/C. These results may be associated with the different methylation forms, mCHH (71.76%) and mCG (57.16%), that accounted for the highest percentages in C/D vs C/C and D/C vs D/D, respectively. In addition, the interspecific grafting superiority was found mainly related to the process of photosynthesis, phytohormone signal transduction, biosynthesis of secondary metabolites, cell wall and transcriptional regulation based on both physiological and molecular results. Overall, the results indicated that the physiological and molecular phenotypes of grafted plants are affected by the interaction between scion and rootstock. Thus, our study provides a theoretical basis for developing suitable scion-rootstock combinations for grafted plants.

Stem xylem traits and wood formation affect sex-specific responses to drought and rewatering in Populus cathayana

The increased frequency and intensity of drought pose great threats to the survival of trees, especially in dioecious tree species with sexual differences in mortality and biased sex ratios. The sex-specific mechanisms underlying stem xylem anatomy and function and carbon metabolism in drought resistance and recovery were investigated in dioecious Populus cathayana Rehder. The sex-specific drought resistance and subsequent recovery were linked to the xylem anatomy and carbon metabolism. Females had a greater xylem vessel area per vessel, biomass and theoretically hydraulic efficiency under well-watered conditions. Conversely, males had a lower xylem lumen area, but greater vessel numbers, and a higher cell wall thickness, suggesting a theoretically conservative water-use strategy and drought resistance. The recovery of photosynthetic ability after drought in males was largely dependent on the recovery of xylem function and the regulation of the xylem carbohydrate metabolism. Additionally, the number of upregulated genes related to xylem cell wall biogenesis was greater in males relative to females under drought stress and subsequent rewatering, which facilitated drought resistance and xylem function restoration in males. These results suggested that sex-specific drought resistance and restoration were related to xylem anatomy and function, carbohydrate metabolism and cell turgor maintenance.

Integrative Metabolome and Transcriptome Analysis of Flavonoid Biosynthesis Genes in Broussonetia papyrifera Leaves From the Perspective of Sex Differentiation

Flavonoids are important secondary metabolites involved in plant development and environmental responses. Sex differences in flavonoids are common in plants. Broussonetia papyrifera is a dioecious plant that is rich in flavonoids. However, few studies have been done on its molecular mechanism, especially sex differences. In the present study, we performed an integrated transcriptomics and metabolomics analysis of the sex differences in the accumulation of flavonoids in B. papyrifera leaves at different developmental stages. In general, flavonoids accumulated gradually with developmental time, and the content in female plants was higher than that in male plants. The composition of flavonoids in female and male plants was similar, and 16 kinds of flavonoids accumulated after flowering. Correspondingly, a significant enrichment of differentially expressed genes and metabolites was observed in the flavonoid biosynthesis pathway. WGCNA and qRT-PCR analyses identified several key genes regulating the accumulation of flavonoids, such as those encoding CHS, CHI and DFR. In addition, 8 TFs were found to regulate flavonoid biosynthesis by promoting the expression of multiple structural genes. These findings provide insight into flavonoid biosynthesis in B. papyrifera associated molecular regulation.

Lack of coordination between stomatal and vein traits provides functional benefits to the dioecious tropical tree Myrsine coriacea

Climate change will affect the distribution of many tropical plant species. However, the understanding of how dioecious tropical species cope with different environmental conditions is still limited. To address this issue, we investigated how secondary trait attributes in populations of the dioecious tropical tree Myrsine coriacea change along an altitudinal gradient. Eighty individual plants (40 male and 40 female) were selected among seven natural populations. Leaf variation in morphological and stomatal traits, and carbon and nitrogen isotopic compositions were analyzed. Female plants had greater isotopic leaf carbon composition (δ¹³ C) and nitrogen content than male plants, increasing their carboxylation capacity. Plants of both sexes had smaller stomata, greater water-use efficiency (greater δ¹³ C), and greater nitrogen isotopic composition (δ¹⁵ N) at higher altitudes. They also showed lower δ¹⁵ N and had greater carbon: nitrogen ratios at lower altitudes. There was a lack of coordination between stomatal and vein traits, which was compensated for by variation in specific leaf areas. This mechanism was essential for increasing plant performance under the limiting conditions found by the species at higher altitudes.

Seed Quantity or Quality?-Reproductive Responses of Females of Two Dioecious Woody Species to Long-Term Fertilisation

Although seed quality and quantity, as well as reproductive performance are important life history stages of plants, little is known about the reproductive responses of trees to environmental changes such as increased anthropogenic deposition of nitrogen (N) and phosphorus (P). Dioecious plants are good models with which to test the environmental impact on female or male reproductive responses individually. We analysed effects of different long-term nutritional availability on the reproductive performance of two dioecious species (Taxus baccata L. and Juniperus communis L.) characterised by different life histories. By using pot experiments with vegetatively propagated plants grown in different fertilisation conditions, we observed an increase in plant growth and strobili production but a decrease in seed efficiency. Seeds produced by fertilised plants had greater seed mass. Fertiliser addition did not change C or N content nor the C/N ratio of T. baccata seeds, but increased N content and the N/P ratio; however, it did lower the C/N ratio in J. communis. Fertilisation did not change the metabolite profile in T. baccata but 18 metabolites were changed in J. communis. The study revealed new links between species life history, environmental changes, and reproduction. The findings imply that future environmental conditions may alter both seed productivity, and quality, as well as plant reproductive behaviour.

Sex-specific nitrogen allocation tradeoffs in the leaves of Populus cathayana cuttings under salt and drought stress

Nitrogen (N) partitioning within a leaf affects leaf photosynthesis and adaptation to environmental fluctuations. However, how plant sex influences leaf N allocation and its tradeoffs in acclimation to drought, excess salt and their combination remains unknown. Here, leaf N allocation between the photosynthetic and non-photosynthetic apparatus and among the components of the photosynthesis in Populus cathayana Rehder females and males were investigated under drought, salt and their combination to clarify the underlying mechanism. We found that males with a lower leaf N allocation (N_L) into non-protein N (N_np), showed a greater leaf N allocation into photosynthetic apparatus, especially into the carboxylation component under all treatments, and a greater leaf N allocation into cell wall under drought and salt stress alone, consequently causing higher photosynthetic N use efficiency (PNUE) and tolerance to stresses. Conversely, females had a greater leaf N allocation into N_np under all treatments than males and a lower leaf photosynthetic N (N_P) allocation. There was a tradeoff in leaf N allocation among photosynthetic apparatus (N_P/N_L), cell wall (N_CW/N_L) and N_np, which explained plant responses to drought, salt and their combination. Moreover, the leaf N allocation into the carboxylation component could explain the intersexual difference in responses to all treatments, while leaf cell wall N (N_CW) and N_np reflected intrasexual differences among treatments in both sexes. These findings indicate sex-specific strategies in coping with drought, salt and their combination that relate to leaf N allocation, which may contribute to sex-specific photosynthesis and niche segregation.

Role of female-predominant MYB39-bHLH13 complex in sexually dimorphic accumulation of taxol in Taxus media

Taxus trees are major natural sources for the extraction of taxol, an anti-cancer agent used worldwide. Taxus media is a dioecious woody tree with high taxol yield. However, the sexually dimorphic accumulation of taxoids in T. media is largely unknown. Our study revealed high accumulation of taxoids in female T. media trees using a UPLC-MS/MS method. Thereafter, many differential metabolites and genes between female and male T. media trees were identified using metabolomic and transcriptomic analyses, respectively. Most of the taxol-related genes were predominantly expressed in female trees. A female-specific R2R3-MYB transcription factor gene, TmMYB39, was identified. Furthermore, bimolecular fluorescence complementation and yeast two-hybrid assays suggested the potential interaction between TmMYB39 and TmbHLH13. Several taxol biosynthesis-related promoter sequences were isolated and used for the screening of MYB recognition elements. The electrophoretic mobility shift assay indicated that TmMYB39 could bind to the promoters of the GGPPS, T10OH, T13OH, and TBT genes. Interaction between TmMYB39 and TmbHLH13 transactivated the expression of the GGPPS and T10OH genes. TmMYB39 might function in the transcriptional regulation of taxol biosynthesis through an MYB-bHLH module. Our results give a potential explanation for the sexually dimorphic biosynthesis of taxol in T. media.

Morphological, physiological, and transcriptional responses to low nitrogen stress in Populus deltoides Marsh. clones with contrasting nitrogen use efficiency

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 NH₄NO₃) and normal N supply (750 μM NH₄NO₃). 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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07991-7.