Impact of polyploidy on plant tolerance to abiotic and biotic stresses

Harnessing cold adaptation for postglacial colonisation: Galactinol synthase expression and raffinose accumulation in a polyploid and its progenitors

Allotetraploid white clover (Trifolium repens) formed during the last glaciation through hybridisation of two European diploid progenitors from restricted niches: one coastal, the other alpine. Here, we examine which hybridisation-derived molecular events may have underpinned white clover's postglacial niche expansion. We compared the transcriptomic frost responses of white clovers (an inbred line and an alpine-adapted ecotype), extant descendants of its progenitor species and a resynthesised white clover neopolyploid to identify genes that were exclusively frost-induced in the alpine progenitor and its derived subgenomes. From these analyses we identified galactinol synthase, the rate-limiting enzyme in biosynthesis of the cryoprotectant raffinose, and found that the extant descendants of the alpine progenitor as well as the neopolyploid white clover rapidly accumulated significantly more galactinol and raffinose than the coastal progenitor under cold stress. The frost-induced galactinol synthase expression and rapid raffinose accumulation derived from the alpine progenitor likely provided an advantage during early postglacial colonisation for white clover compared to its coastal progenitor.

Investigating historical drivers of latitudinal gradients in polyploid plant biogeography: A multiclade perspective

PREMISE

The proportion of polyploid plants in a community increases with latitude, and different hypotheses have been proposed about which factors drive this pattern. Here, we aimed to understand the historical causes of the latitudinal polyploidy gradient using a combination of ancestral state reconstruction methods. Specifically, we assessed whether (1) polyploidization enables movement to higher latitudes (i.e., polyploidization precedes occurrences in higher latitudes) or (2) higher latitudes facilitate polyploidization (i.e., occurrence in higher latitudes precedes polyploidization).

METHODS

We reconstructed the ploidy states and ancestral niches of 1032 angiosperm species at four paleoclimatic time slices ranging from 3.3 million years ago to the present, comprising taxa from four well-represented clades: Onagraceae, Primulaceae, Solanum (Solanaceae), and Pooideae (Poaceae). We used ancestral niche reconstruction models alongside a customized discrete character evolution model to allow reconstruction of states at specific time slices. Patterns of latitudinal movement were reconstructed and compared in relation to inferred ploidy shifts.

RESULTS

No single hypothesis applied equally well across all analyzed clades. While significant differences in median latitudinal occurrence were detected in the largest clade, Poaceae, no significant differences were detected in latitudinal movement in any clade.

CONCLUSIONS

Our preliminary study is the first to attempt to connect ploidy changes to continuous latitudinal movement, but we cannot favor one hypothesis over another. Given that patterns seem to be clade-specific, more clades must be analyzed in future studies for generalities to be drawn.

Halophytes and heavy metals: A multi-omics approach to understand the role of gene and genome duplication in the abiotic stress tolerance of Cakile maritima

PREMISE

The origin of diversity is a fundamental biological question. Gene duplications are one mechanism that provides raw material for the emergence of novel traits, but evolutionary outcomes depend on which genes are retained and how they become functionalized. Yet, following different duplication types (polyploidy and tandem duplication), the events driving gene retention and functionalization remain poorly understood. Here we used Cakile maritima, a species that is tolerant to salt and heavy metals and shares an ancient whole-genome triplication with closely related salt-sensitive mustard crops (Brassica), as a model to explore the evolution of abiotic stress tolerance following polyploidy.

METHODS

Using a combination of ionomics, free amino acid profiling, and comparative genomics, we characterize aspects of salt stress response in C. maritima and identify retained duplicate genes that have likely enabled adaptation to salt and mild levels of cadmium.

RESULTS

Cakile maritima is tolerant to both cadmium and salt treatments through uptake of cadmium in the roots. Proline constitutes greater than 30% of the free amino acid pool in C. maritima and likely contributes to abiotic stress tolerance. We find duplicated gene families are enriched in metabolic and transport processes and identify key transport genes that may be involved in C. maritima abiotic stress tolerance.

CONCLUSIONS

These findings identify pathways and genes that could be used to enhance plant resilience and provide a putative understanding of the roles of duplication types and retention on the evolution of abiotic stress response.

Exploring the patterns of evolution: Core thoughts and focus on the saltational model

The Modern Synthesis, a pillar in biological thought, united Darwin's species origin concepts with Mendel's laws of character heredity, providing a comprehensive understanding of evolution within species. Highlighting phenotypic variation and natural selection, it elucidated the environment's role as a selective force, shaping populations over time. This framework integrated additional mechanisms, including genetic drift, random mutations, and gene flow, predicting their cumulative effects on microevolution and the emergence of new species. Beyond the Modern Synthesis, the Extended Evolutionary Synthesis expands perspectives by recognizing the role of developmental plasticity, non-genetic inheritance, and epigenetics. We suggest that these aspects coexist in the plant evolutionary process; in this context, we focus on the saltational model, emphasizing how saltation events, such as dichotomous saltation, chromosomal mutations, epigenetic phenomena, and polyploidy, contribute to rapid evolutionary changes. The saltational model proposes that certain evolutionary changes, such as the rise of new species, may result suddenly from single macromutations rather than from gradual changes in DNA sequences and allele frequencies within a species over time. These events, observed in domesticated and wild higher plants, provide well-defined mechanistic bases, revealing their profound impact on plant diversity and rapid evolutionary events. Notably, next-generation sequencing exposes the likely crucial role of allopolyploidy and autopolyploidy (saltational events) in generating new plant species, each characterized by distinct chromosomal complements. In conclusion, through this review, we offer a thorough exploration of the ongoing dissertation on the saltational model, elucidating its implications for our understanding of plant evolutionary processes and paving the way for continued research in this intriguing field.

The antagonistic relationship between apoptosis and polyploidy in development and cancer

One of the important functions of regulated cell death is to prevent cells from inappropriately acquiring extra copies of their genome, a state known as polyploidy. Apoptosis is the primary cell death mechanism that prevents polyploidy, and defects in this apoptotic response can result in polyploid cells whose subsequent error-prone chromosome segregation are a major contributor to genome instability and cancer progression. Conversely, some cells actively repress apoptosis to become polyploid as part of normal development or regeneration. Thus, although apoptosis prevents polyploidy, the polyploid state can actively repress apoptosis. In this review, we discuss progress in understanding the antagonistic relationship between apoptosis and polyploidy in development and cancer. Despite recent advances, a key conclusion is that much remains unknown about the mechanisms that link apoptosis to polyploid cell cycles. We suggest that drawing parallels between the regulation of apoptosis in development and cancer could help to fill this knowledge gap and lead to more effective therapies.

Neopolyploidy-induced changes in giant duckweed (Spirodela polyrhiza) alter herbivore preference and performance and plant population performance

PREMISE

Polyploidy is a widespread mutational process in angiosperms that may alter population performance of not only plants but also their interacting species. Yet, knowledge of whether polyploidy affects plant-herbivore dynamics is scarce. Here, we tested whether aphid herbivores exhibit preference for diploid or neopolyploid plants, whether polyploidy impacts plant and herbivore performance, and whether these interactions depend on the plant genetic background.

METHODS

Using independently synthesized neotetraploid strains paired with their diploid progenitors of greater duckweed (Spirodela polyrhiza), we evaluated the effect of neopolyploidy on duckweed's interaction with the water-lily aphid (Rhopalosiphum nymphaeae). Using paired-choice experiments, we evaluated feeding preference of the herbivore. We then evaluated the consequences of polyploidy on aphid and plant performance by measuring population growth over multiple generations.

RESULTS

Aphids preferred neopolyploids when plants were provided at equal abundances but not at equal surface areas, suggesting the role of plant population surface area in driving this preference. Additionally, neopolyploidy increased aphid population performance, but this result was dependent on the plant's genetic lineage. Lastly, the impact of herbivory on neopolyploid vs. diploid duckweed varied greatly with genetic lineage, where neopolyploids appeared to be variably tolerant compared to diploids, sometimes mirroring the effect on herbivore performance.

CONCLUSIONS

By experimentally testing the impacts of polyploidy on trophic species interactions, we showed that polyploidization can impact the preference and performance of herbivores on their plant hosts. These results have significant implications for the establishment and persistence of plants and herbivores in the face of plant polyploidy.

Polyploid Cancer Cell Models in Drosophila

Cells with an abnormal number of chromosomes have been found in more than 90% of solid tumors, and among these, polyploidy accounts for about 40%. Polyploidized cells most often have duplicate centrosomes as well as genomes, and thus their mitosis tends to promote merotelic spindle attachments and chromosomal instability, which produces a variety of aneuploid daughter cells. Polyploid cells have been found highly resistant to various stress and anticancer therapies, such as radiation and mitogenic inhibitors. In other words, common cancer therapies kill proliferative diploid cells, which make up the majority of cancer tissues, while polyploid cells, which lurk in smaller numbers, may survive. The surviving polyploid cells, prompted by acute environmental changes, begin to mitose with chromosomal instability, leading to an explosion of genetic heterogeneity and a concomitant cell competition and adaptive evolution. The result is a recurrence of the cancer during which the tenacious cells that survived treatment express malignant traits. Although the presence of polyploid cells in cancer tissues has been observed for more than 150 years, the function and exact role of these cells in cancer progression has remained elusive. For this reason, there is currently no effective therapeutic treatment directed against polyploid cells. This is due in part to the lack of suitable experimental models, but recently several models have become available to study polyploid cells in vivo. We propose that the experimental models in Drosophila, for which genetic techniques are highly developed, could be very useful in deciphering mechanisms of polyploidy and its role in cancer progression.

Genomic asymmetric epigenetic modification of transposable elements is involved in gene expression regulation of allopolyploid Brassica napus

Polyploids are common and have a wide geographical distribution and environmental adaptability. Allopolyploidy may lead to the activation of transposable elements (TE). However, the mechanism of epigenetic modification of TEs in the establishment and evolution of allopolyploids remains to be explored. We focused on the TEs of model allopolyploid Brassica napus (An An Cn Cn ), exploring the TE characteristics of the genome, epigenetic modifications of TEs during allopolyploidization, and regulation of gene expression by TE methylation. In B. napus, approximately 50% of the genome was composed of TEs. TEs increased with proximity to genes, especially DNA transposons. TE methylation levels were negatively correlated with gene expression, and changes in TE methylation levels were able to regulate the expression of neighboring genes related to responses to light intensity and stress, which promoted powerful adaptation of allopolyploids to new environments. TEs can be synergistically regulated by RNA-directed DNA methylation pathways and histone modifications. The epigenetic modification levels of TEs tended to be similar to those of the diploid parents during the genome evolution of B. napus. The TEs of the An subgenome were more likely to be modified, and the imbalance in TE number and epigenetic modification level in the An and Cn subgenomes may lead to the establishment of subgenome dominance. Our study analyzed the characteristics of TE location, DNA methylation, siRNA, and histone modification in B. napus and highlighted the importance of TE epigenetic modifications during the allopolyploidy process, providing support for revealing the mechanism of allopolyploid formation and evolution.

Synthetic polyploid induction influences morphological, physiological, and photosynthetic characteristics in Melissa officinalis L

Melissa officinalis L., a well-known herb with diverse industrial and ethnopharmacological properties. Although, there has been a significant lack in the breeding attempts of this invaluable herb. This study aimed to enhance the agronomical traits of M. officinalis through in vitro polyploidization. Nodal segments were micropropagated and subjected to oryzalin treatment at concentrations of 20, 40, and 60 mM for 24 and 48 hours. Flow cytometry, chromosome counting, and stomatal characteristics were employed to confirm the ploidy level of the surviving plants. The survival rate of the treated explants decreased exponentially with increasing oryzalin concentration and duration. The highest polyploid induction rate (8%) was achieved with 40 mM oryzalin treatment for 24 hours. The induced tetraploid plants exhibited vigorous growth, characterized by longer shoots, larger leaves, and a higher leaf count. Chlorophyll content and fluorescence parameters elucidated disparities in photosynthetic performance between diploid and tetraploid genotypes. Tetraploid plants demonstrated a 75% increase in average essential oil yield, attributed to the significantly larger size of peltate trichomes. Analysis of essential oil composition in diploid and tetraploid plants indicated the presence of three major components: geranial, neral, and citronellal. While citronellal remained consistent, geranial and neral increased by 11.06% and 9.49%, respectively, in the tetraploid population. This effective methodology, utilizing oryzalin as an anti-mitotic agent for polyploid induction in M. officinalis, resulted in a polyploid genotype with superior morpho-physiological traits. The polyploid lemon balm generated through this method has the potential to meet commercial demands and contribute significantly to the improvement of lemon balm cultivation.

Cytological observation and RNA-seq analysis reveal novel miRNAs high expression associated with the pollen fertility of neo-tetraploid rice

BACKGROUND

Neo-tetraploid rice lines exhibit high fertility and strong heterosis and harbor novel specific alleles, which are useful germplasm for polyploid rice breeding. However, the mechanism of the fertility associated with miRNAs remains unknown. In this study, a neo-tetraploid rice line, termed Huaduo21 (H21), was used. Cytological observation and RNA-sequencing were employed to identify the fertility-related miRNAs in neo-tetraploid rice.

RESULTS

H21 showed high pollen fertility (88.08%), a lower percentage of the pollen mother cell (PMC) abnormalities, and lower abnormalities during double fertilization and embryogenesis compared with autotetraploid rice. A total of 166 non-additive miRNAs and 3108 non-additive genes were detected between H21 and its parents. GO and KEGG analysis of non-additive genes revealed significant enrichments in the DNA replication, Chromosome and associated proteins, and Replication and repair pathways. Comprehensive multi-omics analysis identified 32 pairs of miRNA/target that were associated with the fertility in H21. Of these, osa-miR408-3p and osa-miR528-5p displayed high expression patterns, targeted the phytocyanin genes, and were associated with high pollen fertility. Suppression of osa-miR528-5p in Huaduo1 resulted in a low seed set and a decrease in the number of grains. Moreover, transgenic analysis implied that osa-MIR397b-p3, osa-miR5492, and osa-MIR5495-p5 might participate in the fertility of H21.

CONCLUSION

Taken together, the regulation network of fertility-related miRNAs-targets pairs might contribute to the high seed setting in neo-tetraploid rice. These findings enhance our understanding of the regulatory mechanisms of pollen fertility associated with miRNAs in neo-tetraploid rice.

The effect of induced polyploidy on phytochemistry, cellular organelles and the expression of genes involved in thymol and carvacrol biosynthetic pathway in thyme (Thymus vulgaris)

Induced polyploidy usually results in larger vegetative and reproductive plant organs. In order to study the effect of chromosome doubling on Thymus vulgaris, three levels of colchicine concentration including 0.1, 0.3 and 0.5% (w/v) were applied for 6, 12 and 24 hours on apical meristem of 2- and 4-leaf seedlings. Ploidy level was evaluated by flow cytometry and microscopic chromosome counting. Chemical composition of essential oils extracted by hydro-distillation was analyzed by gas Chromatography/mass spectrometry (GC/MS) and gas Chromatography (GC). The application of 0.3% colchicine at 4-leaf seedling for 6 hours resulted in the highest survival rate and the highest number of tetraploid plants. Cytogenetic and flow cytometry analyses confirmed the increase of chromosome number from 2n=2x=30 in diploids to 2n=4x=60 in induced tetraploids. Tetraploid plants had larger leaves, taller and thicker stems, dense branching, longer trichome, larger stomata, larger guard cells, and decreased number of stomata. The number of chloroplasts and mitochondria increased significantly in tetraploid plants by 1.66 and 1.63 times, respectively. The expression of CYP71D178, CYP71D180 and CYP71D181 increased in tetraploids by 3.27, 7.39 and 2.15 times, respectively, probably resulting in higher essential oil compounds, as tetraploids outyielded the diploid plants by 64.7% in essential oil, 40.9% in thymol and 18.6% in carvacrol content.

Cell Mutagenic Autopolyploidy Enhances Salinity Stress Tolerance in Leguminous Crops

Salinity stress affects plant growth and development by causing osmotic stress and nutrient imbalances through excess Na+, K+, and Cl- ion accumulations that induce toxic effects during germination, seedling development, vegetative growth, flowering, and fruit set. However, the effects of salt stress on growth and development processes, especially in polyploidized leguminous plants, remain unexplored and scantly reported compared to their diploid counterparts. This paper discusses the physiological and molecular response of legumes towards salinity stress-based osmotic and ionic imbalances in plant cells. A multigenic response involving various compatible solutes, osmolytes, ROS, polyamines, and antioxidant activity, together with genes encoding proteins involved in the signal transduction, regulation, and response mechanisms to this stress, were identified and discussed. This discussion reaffirms polyploidization as the driving force in plant evolution and adaptation to environmental stress constraints such as drought, feverish temperatures, and, in particular, salt stress. As a result, thorough physiological and molecular elucidation of the role of gene duplication through induced autopolyploidization and possible mechanisms regulating salinity stress tolerance in grain legumes must be further studied.

Polyploidy and diploidization in soybean

Polyploidy is widespread and particularly common in angiosperms. The prevalence of polyploidy in the plant suggests it as a crucial driver of diversification and speciation. The paleopolyploid soybean (Glycine max) is one of the most important crops of plant protein and oil for humans and livestock. Soybean experienced two rounds of whole genome duplication around 13 and 59 million years ago. Due to the relatively slow process of post-polyploid diploidization, most genes are present in multiple copies across the soybean genome. Growing evidence suggests that polyploidization and diploidization could cause rapid and dramatic changes in genomic structure and epigenetic modifications, including gene loss, transposon amplification, and reorganization of chromatin architecture. This review is focused on recent progresses about genetic and epigenetic changes during polyploidization and diploidization of soybean and represents the challenges and potentials for application of polyploidy in soybean breeding.

Evaluating the Differential Response of Transcription Factors in Diploid versus Autotetraploid Rice Leaves Subjected to Diverse Saline-Alkali Stresses

Saline-alkali stress is a significant abiotic stress factor that impacts plant growth, development, and crop yield. Consistent with the notion that genome-wide replication events can enhance plant stress resistance, autotetraploid rice exhibited a higher level of tolerance to saline-alkali stress than its donor counterparts, which is reflected by differential gene expression between autotetraploid and diploid rice in response to salt, alkali, and saline-alkali stress. In this study, we investigated the expression of the transcription factors (TFs) in the leaf tissues of autotetraploid and diploid rice under different types of saline-alkali stress. Transcriptome analysis identified a total of 1040 genes from 55 TF families that were altered in response to these stresses, with a significantly higher number in autotetraploid rice compared to diploid rice. Contrarily, under these stresses, the number of expressed TF genes in autotetraploid rice was greater than that in diploid rice for all three types of stress. In addition to the different numbers, the differentially expressed TF genes were found to be from significantly distinct TF families between autotetraploid and diploid rice genotypes. The GO enrichment analysis unraveled that all the DEGs were distributed with differentially biological functions in rice, in particular those that were enriched in the pathways of phytohormones and salt resistance, signal transduction, and physiological and biochemical metabolism in autotetraploid rice compared to its diploid counterpart. This may provide useful guidance for studying the biological roles of polyploidization in plant resilience in response to saline-alkali stress.

Hexaploid Salix rehderiana is more suitable for remediating lead contamination than diploids, especially male plants

Willows are promising candidates for phytoremediation, but the lead (Pb) phytoremediation potential of different willow ploidy and sex has not yet been exploited. In this study, the Pb uptake, translocation and detoxification capacities of hexaploid and diploid, female and male Salix rehderiana were investigated. The results showed that Pb treatment inhibited biomass accumulation and gas exchange, caused ultrastructural and oxidative damage, and induced antioxidant, phytohormonal and transcriptional regulation in S. rehderiana. Absorbed Pb was mainly accumulated in the roots with restricted root-to-shoot transport. Despite lower biomass, greater transpiration, phytohormonal and transcriptional regulation indicated that hexaploid S. rehderiana had higher tissue Pb concentration, total accumulated Pb amount (4.39 mg, 6.19 mg, 6.60 mg and 10.83 mg in diploid and hexaploid females and males, respectively) as well as bioconcentration factors and translocation factors (0.412, 0.593, 0.921 and 1.320 for bioconcentration factors in roots, and 0.029, 0.032, 0.035 and 0.047 for translocation factors in diploid and hexaploid females and males, respectively) than diploids. Higher soil urease and acid phosphatase activities also favored hexaploids to use more available N and P than diploids in Pb-contaminated soils. Additionally, hexaploid S. rehderiana had stronger antioxidant, phytohormonal and transcriptional responses, and displayed less morphological and ultrastructural damage than diploids after Pb treatment, suggesting that hexaploids have greater Pb uptake, translocation and detoxification capacities than diploids. Moreover, S. rehderiana males had greater Pb uptake and translocation abilities, as well as stronger antioxidant, phytohormonal, and transcriptional regulation mediated Pb detoxification capacities than females. Therefore, hexaploid S. rehderiana are superior to diploids, and males are better than females in Pb phytoremediation. This study provides novel and valuable insights for selecting better willow materials to mitigate Pb contamination.

Hydraulic trade-offs underlie enhanced performance of polyploid trees under soil water deficit

The relationships between aerial organ morpho-anatomy of woody polyploid plants with their functional hydraulics under water stress remain largely understudied. We evaluated growth-associated traits, aerial organ xylem anatomy, and physiological parameters of diploid, triploid, and tetraploid genotypes of atemoyas (Annona cherimola x Annona squamosa), which belong to the woody perennial genus Annona (Annonaceae), testing their performance under long-term soil water reduction. The contrasting phenotypes of vigorous triploids and dwarf tetraploids consistently showed stomatal size-density trade-off. The vessel elements in aerial organs were ∼1.5 times wider in polyploids compared with diploids, and triploids displayed the lowest vessel density. Plant hydraulic conductance was higher in well-irrigated diploids while their tolerance to drought was lower. The phenotypic disparity of atemoya polyploids associated with contrasting leaf and stem xylem porosity traits that coordinate to regulate water balances between the trees and the belowground and aboveground environments. Polyploid trees displayed better performance under soil water scarcity, presenting as more sustainable agricultural and forestry genotypes to cope with water stress.

Ecophysiological Differentiation among Two Resurrection Ferns and Their Allopolyploid Derivative

Theoretically, the coexistence of diploids and related polyploids is constrained by reproductive and competitive mechanisms. Although niche differentiation can explain the commonly observed co-occurrence of cytotypes, the underlying ecophysiological differentiation among cytotypes has hardly been studied. We compared the leaf functional traits of the allotetraploid resurrection fern Oeosporangium tinaei (HHPP) and its diploid parents, O. hispanicum (HH) and O. pteridioides (PP), coexisting in the same location. Our experimental results showed that all three species can recover physiological status after severe leaf dehydration, which confirms their 'resurrection' ability. However, compared with PP, HH had much higher investment per unit area of light-capturing surface, lower carbon assimilation rate per unit mass for the same midday water potential, higher non-enzymatic antioxidant capacity, higher carbon content, and lower contents of nitrogen, phosphorus, and other macronutrients. These traits allow HH to live in microhabitats with less availability of water and nutrients (rock crevices) and to have a greater capacity for resurrection. The higher assimilation capacity and lower antioxidant capacity of PP explain its more humid and nutrient-rich microhabitats (shallow soils). HHPP traits were mostly intermediate between those of HH and PP, and they allow the allotetraploid to occupy the free niche space left by the diploids.

Impact of Polyploidy Induction for Salinity Stress Mitigation in Soybean (Glycine max L. Merrill)

Polyploidy induction is recognized as one of the major evolutionary processes leading to remarkable morphological, physiological, and genetic variations in plants. Soybean (Glycine max L.), also known as soja bean or soya bean, is an annual leguminous crop of the pea family (Fabaceae) that shares a paleopolypoidy history, dating back to approximately 56.5 million years ago with other leguminous crops such as cowpea and other Glycine specific polyploids. This crop has been documented as one of the polyploid complex species among legumes whose gene evolution and resultant adaptive growth characteristics following induced polyploidization has not been fully explored. Furthermore, no successfully established in vivo or in vitro based polyploidy induction protocols have been reported to date, particularly, with the intention to develop mutant plants showing strong resistance to abiotic salinity stress. This review, therefore, describes the role of synthetic polyploid plant production in soybean for the mitigation of high soil salt stress levels and how this evolving approach could be used to further enhance the nutritional, pharmaceutical and economic industrial value of soybeans. This review also addresses the challenges involved during the polyploidization process.

The creation of autotetraploid provides insights into critical features of DNA methylome changes after genome doubling in water spinach (Ipomoea aquatica Forsk)

Water spinach (Ipomoea aquatica Forsk) is an essential green leafy vegetable in Asia. In this study, we induced autotetraploid water spinach by colchicine. Furthermore, DNA methylation and transcriptome of tetraploid and diploid were compared using Whole Genome Bisulfite Sequencing (WGBS) and RNA-sequencing techniques. Autotetraploid water spinach was created for the first time. Compared with the diploid parent, autotetraploid water spinach had wider leaves, thicker petioles and stems, thicker and shorter adventitious roots, longer stomas, and larger parenchyma cells. The whole genome methylation level of the autotetraploid was slightly higher than that of the diploid. Compared with the diploid, 12281 Differentially Methylated Regions (DMRs)were found in the autotetraploid, including 2356 hypermethylated and 1310 hypomethylated genes, mainly enriched in 'Arginine and Proline metabolism', 'beta - Alanine metabolism', 'Plant homone signal translation', 'Ribome', and 'Plant - pathgen interaction' pathways. Correlation analysis of transcriptome and DNA methylation data showed that 121 differentially expressed genes undergone differential methylation, related to four pathways 'Other types of O-glycan biosynthesis', 'Terpenoid backbone biosynthesis', 'Biosynthesis of secondary metabolites', and 'Metabolic paths'. This work obtained important autotetraploid resources of water spinach and revealed the genomic DNA methylation changes after genome doubling, being helpful for further studying the molecular mechanism of variations caused by polyploids of the Ipomoea genus.

Autotetraploidization Gives Rise to Differential Gene Expression in Response to Saline Stress in Rice

Plant polyploidization represents an effective means for plants to perpetuate their adaptive advantage in the face of environmental variation. Numerous studies have identified differential responsiveness to environmental cues between polyploids and their related diploids, and polyploids might better adapt to changing environments. However, the mechanism that underlies polyploidization contribution during abiotic stress remains hitherto obscure and needs more comprehensive assessment. In this study, we profile morphological and physiological characteristics, and genome-wide gene expression between an autotetraploid rice and its diploid donor plant following saline stress. The results show that the autotetraploid rice is more tolerant to saline stress than its diploid precursor. The physiological characteristics were rapidly responsive to saline stress in the first 24 h, during which the elevations in sodium ion, superoxide dismutase, peroxidase, and 1-aminocyclopropane-1-carboxylic acid were all significantly higher in the autotetraploid than in the diploid rice. Meanwhile, the genome-wide gene expression analysis revealed that the genes related to ionic transport, peroxidase activity, and phytohormone metabolism were differentially expressed in a significant manner between the autotetraploid and the diploid rice in response to saline stress. These findings support the hypothesis that diverse mechanisms exist between the autotetraploid rice and its diploid donor plant in response to saline stress, providing vital information for improving our understanding on the enhanced performance of polyploid plants in response to salt stress.