Molecular mechanism of thiamine in mitigating drought stress in Chinese wingnut (Pterocarya stenoptera): Insights from transcriptomics

Urban garden plants are frequently affected by drought, which can hinder their growth, development, and greening effect. Previous studies have indicated that Chinese wingnut (Pterocarya stenoptera) responds to drought stress by increasing the expression of thiamine synthesis genes. In this study, it was found that exogenous thiamine can effectively alleviate the negative effects of drought stress on plants. Forward transcriptome sequencing and physiological tests were further conducted to reveal the molecular mechanism of thiamine in alleviating drought stress. Results showed that exogenous thiamine activated the expression of eight chlorophyll synthesis genes in Chinese wingnut under drought stress. Moreover, physiological indicators proved that chlorophyll content increased in leaves of Chinese wingnut with thiamine treatment under drought stress. Photosynthesis genes were also activated in Chinese wingnut treated with exogenous thiamine under drought stress, as supported by photosynthetic indicators PIabs and PItotal. Additionally, exogenous thiamine stimulated the expression of genes in the auxin-activated signaling pathway, thus attenuating the effects of drought stress. This study demonstrates the molecular mechanism of thiamine in mitigating the effects of drought stress on non-model woody plants lacking transgenic systems. This study also provides an effective method to mitigate the negative impacts of drought stress on plants.

Physiological and transcriptional changes provide insights into the effect of root waterlogging on the aboveground part of Pterocarya stenoptera

Pterocarya stenoptera is a tree species that occurs along rivers and has high tolerance to waterlogging. Identification of waterlogging response genes in the aboveground part of P. stenoptera will increase understanding of tolerance mechanisms under root waterlogging conditions. In this study, we employed four physiological indicators and comparative transcriptome sequencing to investigate the waterlogging tolerance mechanism in P. stenoptera. The physiological results showed that the aboveground part of P. stenoptera was not obviously affected by waterlogging. P. stenoptera enhanced waterlogging tolerance by increasing the synthesis of alpha-Linolenic acids and flavonoids and activating the jasmonic acid, ethylene, and auxin signaling pathways. Our results confirmed our hypothesis that P. stenoptera, a species that is widely distributed along rivers, has evolved a range of mechanisms in response to waterlogging. Our research will provide new insights for understanding the tolerance mechanism of species to waterlogging.

Comparative analysis of drought-responsive and -adaptive genes in Chinese wingnut (Pterocarya stenoptera C. DC)

Background

Drought is the main stress factor for the cultivation of Pterocarya stenoptera in urban areas, and this factor will cause its dehydration and affect its growth. Identifying drought-related genes will be useful for understanding the drought adaptation mechanism of P. stenoptera.

Results

We used physiological indicator detection, comparative transcriptome sequencing, and reanalysis on the results of previous landscape genomics studies to investigate the drought adaptation mechanism in P. stenoptera. The changes in malondialdehyde content showed that P. stenoptera was remarkably affected by drought stress, and the increase in soluble sugar content suggested its important role in response to drought stress. Results of comparative transcriptome sequencing showed that P. stenoptera initiated a series of programs, such as increasing the gene expression of unsaturated fatty acids, tyrosine, and plant pathogen resistance, to deal with the transient drought stress. According to the annotated results in a previous study, P. stenoptera adapts to the long-term differential drought stress by regulating the thickness of cell walls and expressing upper or lower limits of the downstream genes in the hormone signaling pathway. Through the comparative analysis of drought-responsive and -adaptive genes in P. stenoptera, this study supports the hypothesis that the environment-responsive genes (ERGs) introduced by the transient environmental stresses will be substantially more than the environment-adaptive genes (EAGs) in response to long-term differential environmental stresses, and the EAGs are not necessarily ERGs.

Conclusions

Our study identified drought-responsive and -adaptive genes in P. stenoptera and revealed that P. stenoptera increased the gene expression of unsaturated fatty acids, tyrosine, and plant pathogen resistance in response to transient drought stress. This study reveals the different adaptation mechanism of P. stenoptera under the transient and long-term differential drought stresses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07470-z.

Physiological analysis and transcriptome sequencing reveal the effects of drier air humidity stress on Pterocarya stenoptera

Identifying physiological and transcriptomic changes can provide insights into the effects of drier air humidity stress on plants. In this study, we selected 6-month-old seedlings of Pterocarya stenoptera as study materials and used physiological index detection and transcriptome sequencing to investigate the adaptation mechanism of P. stenoptera in response to drier air humidity stress. Proline content, and superoxide dismutase and peroxidase activities did not increase significantly under drier air humidity stress. The physiological results showed that the drier air humidity stress only had slight effects on P. stenoptera. However, transcriptome sequencing showed that P. stenoptera initiated a series of metabolic pathways including L-phenylalanine catabolic process, NAD biosynthetic process, ATP biosynthetic process, and thiamine metabolism under drier air humidity stress. The enriched Kyoto Encyclopedia of Genes and Genomes results at 2 and 4 weeks under the drier air humidity stress showed that the genes THI1 and THIC in thiamine metabolism exhibited significantly differential expression. Previous studies confirmed that the two genes can improve drought tolerance. Our results implicitly indicated that exogenous thiamine might improve drought tolerance and alleviate the yellowing of the P. stenoptera leaves. Our study provides insights into the adaptation mechanism of P. stenoptera in response to drier air humidity stress and important clues into the cultivation and management of P. stenoptera in northern cities in China.

Shifts in potential geographical distribution of Pterocarya stenoptera under climate change scenarios in China

Climate change poses a serious threat to biodiversity. Predicting the effects of climate change on the distribution of a species' habitat can help humans address the potential threats which may change the scope and distribution of species. Pterocarya stenoptera is a common fast-growing tree species often used in the ecological restoration of riverbanks and alpine forests in central and eastern China. Until now, the characteristics of the distribution of this species' habitat are poorly known as are the environmental factors that influence its preferred habitat. In the present study, the Maximum Entropy Modeling (Maxent) algorithm and the Genetic Algorithm for Ruleset Production (GARP) were used to establish the models for the potential distribution of this species by selecting 236 sites with known occurrences and 14 environmental variables. The results indicate that both models have good predictive power. Minimum temperature of coldest month (Bio6), mean temperature of warmest quarter (Bio10), annual precipitation (Bio12), and precipitation of driest month (Bio14) were important environmental variables influencing the prediction of the Maxent model. According to the models, the temperate and subtropical regions of eastern China had high environmental suitability for this species, where the species had been recorded. Under each climate change scenario, climatic suitability of the existing range of this species increased, and its climatic niche expanded geographically to the north and higher elevation. GARP predicted a more conservative expansion. The projected spatial and temporal patterns of P. stenoptera can provide reference for the development of forest management and protection strategies.

Characterization of the complete chloroplast genome of Pterocarya stenoptera, a tall deciduous tree of the family Juglandaceae

Pterocarya stenoptera, also called Chinese wingnut in China, is a tall deciduous tree of the walnut family (Juglandaceae). P. stenoptera is one of the most popular shade trees owing to its tall and graceful form and rapid growth rate. In the present study, the chloroplast genome of P. stenoptera was assembled and analyzed phylogenetically. The chloroplast genome of P. stenoptera is 160,212 bp in length, with a large single-copy region (LSC) of 88,724 bp, a small single-copy region (SSC) of 18,396 bp, and a pair of inverted repeat regions (IRs) of 26,046 bp, forming a typical quadripartite structure. A total of 130 genes are annotated from the chloroplast genome of P. stenoptera, including 82 protein-coding genes, 40 transfer RNA (tRNAs) genes, and 8 ribosomal RNA (rRNAs) genes. The GC content of the chloroplast genome is 36.2%. Phylogenetic analysis based on the common proteins from P. stenoptera and 14 related species confirmed the close relationship between Pterocarya and Juglans.

Molecular Phylogeography Analysis Reveals Population Dynamics and Genetic Divergence of a Widespread Tree Pterocarya stenoptera in China

The geological events, past climatic fluctuations, and river systems played key roles in the spatial distribution, population dynamics, and genetic differentiation of species. In this work, we selected Pterocarya stenoptera, a widespread tree species in China, to test the roles of these factors. Four noncoding spacers, eight microsatellite (simple sequence repeat) markers, and species distribution modeling were used to examine the phylogeographical pattern of P. stenoptera. Based on chloroplast DNA data, populations of P. stenoptera were clearly clustered into three groups. The divergence time of these groups fell into the stage of the Qinghai–Tibet Movement, 1.7–2.6 Ma. For simple sequence repeat data, only one western marginal population YNYB could be separated from other populations, whereas other populations were mixed together. Our results indicated that the environmental heterogeneity resulting from the Qinghai–Tibet movement might be response for this genetic divergence. The climatic fluctuations in the Pleistocene did not cause the substantial range shift of P. stenoptera, while the fluctuations affected its population size. Moreover, we also confirmed the river systems did not act as channels or barrier of dispersal for P. stenoptera.

Niche of main woody plant populations of Pterocarya stenoptera community in riparian zone of Lijiang River, China

To understand the niche characteristics of main woody species in Pterocarya stenoptera community, we investigated P. stenoptera communities in riparian zone of Lijiang River, China. The niche characteristics of main species in tree layers and shrub layers were quantified with the indices of Levins niche breadth, Shannon niche breadth, Schoener niche similarities and Pianka niche overlap. The results showed that P. stenoptera in the tree layer, and Ficus abelii and Morus alba in the shrub layer had higher niche breadth than other species. The species with larger importance values generally had larger niche breadth, but the rank orders of which were not exactly the same. The niche similarity of main populations in the tree layer was generally smaller than that in the shrub layer. The mean value of niche similarity of main populations in the tree layer and shrub layer was 0.151 and 0.236, respectively. There was a low degree of niche similarity among species within the community, indicating that they had a low similarity in resource use. The niche overlap of main populations in the tree layer was generally smaller than that in the shrub layer, with the mean value of niche overlap of main populations in the tree layer and shrub layer being 0.217 and 0.273, respectively. The niche overlap between the main species in the community was relatively lower. There was no significant correlation between niche breadth and niche similarity. The species with larger niche breadth often had more opportunities to overlap with other species. However, their overlap value was not necessarily larger. Larger niche similarity was often associated with higher degrees of niche overlap. The P. stenoptera community in riparian zone of Lijiang River was the climax community, the relationship among species was relatively stable, the population regeneration was very slow, and the development trend of this community was declining in the future.

Isolation and characterization of microsatellite loci from Pterocarya stenoptera (Juglandaceae)

PREMISE OF THE STUDY

Microsatellite markers of Pterocarya stenoptera (Juglandaceae) were developed for future studies on the population genetic diversity and spatial genetic structure of the species.

METHODS AND RESULTS

Based on Illumina sequencing of the transcriptome of P. stenoptera, a total of 2452 microsatellites were identified from 83,674 assembled unigenes. One hundred microsatellites were randomly selected to design amplification primer pairs. Of these, 15 were successfully amplified and displayed polymorphism. For these markers, the number of alleles per locus and population ranged from one to six. The levels of observed and expected heterozygosity varied from 0.000 to 1.000 and 0.000 to 0.718, respectively. Furthermore, all of the 15 loci were successfully cross-amplified in another congeneric species (P. hupehensis) and were demonstrated to be polymorphic.

CONCLUSIONS

The microsatellite loci described here can be used for future population genetic and landscape genetic studies on P. stenoptera.

Adaptive genetic differentiation in Pterocarya stenoptera (Juglandaceae) driven by multiple environmental variables were revealed by landscape genomics

BACKGROUND

The investigation of the genetic basis of local adaptation in non-model species is an interesting focus of evolutionary biologists and molecular ecologists. Identifying these adaptive genetic variabilities on the genome responsible can provide insight into the genetic mechanism of local adaptation.

RESULTS

We investigated the spatial distribution of genetic variation in 22 natural populations of Pterocarya stenoptera across its distribution area in China to provide insights into the complex interplay between multiple environmental variables and adaptive genetic differentiation. The Bayesian analysis of population structure showed that the 22 populations of P. stenoptera were subdivided into two groups. Redundancy analysis demonstrated that this genetic differentiation was caused by the divergent selection of environmental difference. A total of 44 outlier loci were mutually identified by Arlequin and BayeScan, 43 of which were environment-associated loci (EAL). The results of latent factor mixed model analysis showed that solar radiation in June (Sr6), minimum temperature of the coldest month (Bio6), temperature seasonality (Bio4), and water vapor pressure in January (Wvp1) were associated with the highest numbers of EAL. Sr6 was associated with the ecological habitat of "prefered light", and Bio6 and Wvp1 were associated with the ecological habitat of "warm and humid environment".

CONCLUSIONS

Our results provided empirical evidence that environmental variables related to the ecological habitats of species play key roles in driving adaptive differentiation of species genome.