Analysis of DNA methylation related to rice adult plant resistance to bacterial blight based on methylation-sensitive AFLP (MSAP) analysis

Integrative transcriptome and WGCNA analysis reveal key genes mainly in response to Alternaria alternata in Populus simonii × P. nigra

In order to explore the molecular mechanisms of Populus simonii × P. nigra response to stress and screen for genes conferring resistance to Alternaria alternata, we carried out measurements of physiological and biochemical indices and transcriptomic sequence analysis of leaves of Populus simonii × P. nigra inoculated with A. alternata. The results showed that the variation trends of multiple hormone contents and enzyme activities were broadly similar at different time points, with H2O2, SA, JA, PPO, SOD, PAL and POD showing a trend of increasing and then decrease after inoculation with the pathogen. The contents of H2O2 peaked on the second day and subsequently declined. The contents of SA and JA, as well as the enzymatic activities of SOD, PAL, and POD, reached their maxima on the third day before exhibiting a downward tendency. In contrast, the activity of PPO peaked on the fourth day. Whereas ABA content continued to increase until the fifth day and CAT content decreased and then increased. We subsequently identified 14,997 differentially expressed genes (DEGs) among the transcriptomic sequences(|log2FoldChange| > 1 and FDR value < 0.05), with genes encoding members of the ERF, MYB, bZIP, and WRKY transcription factor families being differentially expressed. Gene modules that were significantly associated with the ABA, PAL, JA, and SOD activity were identified using weighted gene co-expression network analysis (WGCNA). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that these genes were mainly related to biological stress, signal transduction, cell wall, and photosynthesis. Within these modules, we also identified hub genes in the regulatory network, including GLK1/2 transcriptional activators, 14-3-3 proteins, cytosine 5 methyltransferases, and a variety of proteins associated with photosynthesis and respiration. This study showed that these hub genes, which play a pivotal role in the co-expression network, which may indicate a potential role in defense process of Populus simonii × P. nigra against A. alternata. Additionally, we analyzed the gene expression regulation and defense mechanisms of Populus simonii × P. nigra adversity stress, providing new insights into how plants respond to biological stress.

Epigenome editing for targeted DNA (de)methylation: a new perspective in modulating gene expression

Traditionally, it has been believed that inheritance is driven as phenotypic variations resulting from changes in DNA sequence. However, this paradigm has been challenged and redefined in the contemporary era of epigenetics. The changes in DNA methylation, histone modification, non-coding RNA biogenesis, and chromatin remodeling play crucial roles in genomic functions and regulation of gene expression. More importantly, some of these changes are inherited to the next generations as a part of epigenetic memory and play significant roles in gene expression. The sum total of all changes in DNA bases, histone proteins, and ncRNA biogenesis constitutes the epigenome. Continuous progress in deciphering epigenetic regulations and the existence of heritable epigenetic/epiallelic variations associated with trait of interest enables to deploy epigenome editing tools to modulate gene expression. DNA methylation marks can be utilized in epigenome editing for the manipulation of gene expression. Initially, genome/epigenome editing technologies relied on zinc-finger protein or transcriptional activator-like effector protein. However, the discovery of clustered regulatory interspaced short palindromic repeats CRISPR)/deadCRISPR-associated protein 9 (dCas9) enabled epigenome editing to be more specific/efficient for targeted DNA (de)methylation. One of the major concerns has been the off-target effects, wherein epigenome editing may unintentionally modify gene/regulatory element which may cause unintended change/harmful effects. Moreover, epigenome editing of germline cell raises several ethical/safety issues. This review focuses on the recent developments in epigenome editing tools/techniques, technological limitations, and future perspectives of this emerging technology in therapeutics for human diseases as well as plant improvement to achieve sustainable developmental goals.

Analysis of the Genetic Diversity in Tea Plant Germplasm in Fujian Province Based on Restriction Site-Associated DNA Sequencing

Fujian province, an important tea-producing area in China, has abundant tea cultivars. To investigate the genetic relationships of tea plant cultivars in Fujian province and the characteristics of the tea plant varieties, a total of 70 tea cultivars from Fujian and other 12 provinces in China were subjected to restriction site-associated DNA sequencing (RAD-seq). A total of 60,258,975 single nucleotide polymorphism (SNP) sites were obtained. These 70 tea plant cultivars were divided into three groups based on analyzing the phylogenetic tree, principal component, and population structure. Selection pressure analysis indicated that nucleotide diversity was high in Southern China and genetically distinct from cultivars of Fujian tea plant cultivars, according to selection pressure analysis. The selected genes have significant enrichment in pathways associated with metabolism, photosynthesis, and respiration. There were ten characteristic volatiles screened by gas chromatography-mass spectrometry (GC-MS) coupled with multivariate statistical methods, among which the differences in the contents of methyl salicylate, 3-carene, cis-3-hexen-1-ol, (E)-4-hexen-1-ol, and 3-methylbutyraldehyde can be used as reference indicators of the geographical distribution of tea plants. Furthermore, a metabolome genome-wide association study (mGWAS) revealed that 438 candidate genes were related to the aroma metabolic pathway. Further analysis showed that 31 genes of all the selected genes were screened and revealed the reasons for the genetic differences in aroma among tea plant cultivars in Fujian and Southern China. These results reveal the genetic diversity in the Fujian tea plants as well as a theoretical basis for the conservation, development, and utilization of the Fujian highly aromatic tea plant cultivars.

Genome-wide DNA methylation analysis reveals layer-specific methylation patterns in deer antler tissue

This paper explored using of deer antlers as a model for studying rapid growth and cartilage formation in mammals. The genes and regulatory mechanisms involved in antler chondrogenesis are poorly understood, however, previous research has suggested that DNA methylation played a key role in antler regeneration. By using fluorescence-labeled methylation-sensitive amplified polymorphism (F-MSAP), this study measured DNA methylation levels in cartilage (CA) and reserve mesenchyme (RM) cells and tissues. Results showed that RM cells (RMCs) DNA methylation levels were significantly lower than those of CA, suggesting that DNA demethylation may be involved in antler fast cartilage differentiation. The study also identified 20 methylated fragments specific to RMCs or CA using the methylation-sensitive amplified polymorphism (MSAP) technique and confirmed these findings using southern blot analysis. The data provide the first experimental evidence of a link between epigenetic regulation and rapid cartilage differentiation in antlers.

The challenge of managing yellow rust (Puccinia striiformis f.sp. tritici) in winter wheat: how combined climate and pathogen stressors impact variability in genotype reactions

Despite the ongoing evolution of wheat pathogens due to the selection pressures of agro-ecological conditions, many studies have often overlooked the combined impact of both biotic and abiotic factors on disease occurrence. From 2016 to 2023, a comprehensive screening of obligate pathogens, including B. graminis f. sp. tritici, P. graminis f. sp. tritici, P. triticina, and P. striiformis f. sp. tritici, was carried out. This screening was conducted on a phenotyping platform encompassing 2715 winter wheat genotypes and their wild relatives, both with and without resistant genes (Lr, Yr, and Sr) for rust diseases. The data were analyzed using PCAmix, best subsets regression, and linear regression modeling. The findings from this study reveal that the plant reactions to leaf and yellow rust infections is far from straightforward. It is heavily influenced not only by prevalent rust races and climatic factors that impact pathogen life cycles but also by variations in the susceptibility reactions of wheat genotypes to the broader agro-ecological conditions. We also observed a tendency for leaf rust and yellow rust to coexist within the same host plant, even though yellow rust is typically considered more aggressive. We reported for the first time genes related to yellow rust resistance breakdown in Serbia in 2023. Lastly, we underscored the importance of investigating resistance responses to rust diseases not exclusively through the interrelation between resistance genes and pathogen virulence, but also by considering how plants respond to the combined stresses of abiotic and biotic factors. Consequently, our study sets the groundwork for further research into how plants respond to multiple stressors and contributes for further investigations related with effective integrated rust management.

Comparative DNA Methylome of Phytoplasma Associated Retrograde Metamorphosis in Sesame (Sesamum indicum L.)

Phytoplasma-associated diseases such as phyllody and little leaf are critical threats to sesame cultivation worldwide. The mechanism of the dramatic conversion of flowers to leafy structures leading to yield losses and the drastic reduction in leaf size due to Phytoplasma infection remains yet to be identified. Cytosine methylation profiles of healthy and infected sesame plants studied using Whole Genome Bisulfite Sequencing (WGBS) and Quantitative analysis of DNA methylation with the real-time PCR (qAMP) technique revealed altered DNA methylation patterns upon infection. Phyllody was associated with global cytosine hypomethylation, though predominantly in the CHH (where H = A, T or C) context. Interestingly, comparable cytosine methylation levels were observed between healthy and little leaf-affected plant samples in CG, CHG and CHH contexts. Among the different genomic fractions, the highest number of differentially methylated Cytosines was found in the intergenic regions, followed by promoter, exonic and intronic regions in decreasing order. Further, most of the differentially methylated genes were hypomethylated and were mainly associated with development and defense-related processes. Loci for STOREKEEPER protein-like, a DNA-binding protein and PP2-B15, an F-Box protein, responsible for plugging sieve plates to maintain turgor pressure within the sieve tubes were found to be hypomethylated by WGBS, which was confirmed by methylation-dependent restriction digestion and qPCR. Likewise, serine/threonine-protein phosphatase-7 homolog, a positive regulator of cryptochrome signaling involved in hypocotyl and cotyledon growth and probable O-methyltransferase 3 locus were determined to be hypermethylated. Phytoplasma infection-associated global differential methylation as well as the defense and development-related loci reported here for the first time significantly elucidate the mechanism of phytoplasma-associated disease development.

Exploring japonica rice epigenetic diversity in the main production regions of Heilongjiang Province

As a major epigenetic modification, DNA methylation plays an important role in coordinating plant responses to environmental changes. Methylation-sensitive amplified polymorphism (MSAP) technology was used in this study to investigate the epigenetic diversity of fifty japonica rice samples from five regions in Heilongjiang Province, China. In addition, the phenotypic indicators of japonica rice samples and the environmental conditions of the sampling sites were investigated and analysed. Based on the MSAP analysis technique, using eight pairs of selective primers, we identified a total of 551 amplified loci, of which 267 (48.5%) were classified as methylation loci. The methylation status and levels of the japonica rice genome in different regions differed significantly (p < 0.05). The results of the analysis of molecular variance (AMOVA) revealed that most of the molecular variation (91%) came from within the groups (regions) and was caused by individual variation within the region. Furthermore, the results of principal coordinates analysis (PCoA), cluster analysis, and population structure analysis indicated that there was no obvious correlation between the epigenetic differences and geographical locations, which may have been due to the limited range of sampling sites. When environmental factors, phenotypic indicators, and epigenetic data analysis are combined, it is easy to conclude that japonica rice grown in the same latitudinal region has increased epigenetic and phenotypic similarities due to similar climatic conditions and production practices.

Auxin drives tomato spotted wilt virus (TSWV) resistance through epigenetic regulation of auxin response factor ARF8 expression in tomato

Tomato spotted wilt virus (TSWV) causes severe losses of tomato crops worldwide. To cope dynamically with such a threat, plants deploy strategies acting at the molecular and the epigenetic levels. We found that tomato symptoms progress in a specific-genotype-manner upon TSWV infection. Susceptible genotypes showed within the Auxin Response Factor (ARF8) promoter coupled to enhanced expression of miRNA167a, reduced ARF8 gene and decreased levels of the hormone auxin. This constitutes a deliberate attempt of TSWV to disrupt plant growth to promote spread in sensitive cultivars. Epigenetic regulation through the level of cytosine methylation and the miR167a-ARF8 module are part of a complex network modulating auxin-triggered synthesis and shaping tomato responses to TSWV. Furthermore, modulation of miR167a-ARF8 regulatory module could be applied in tomato-resistance breeding programs.

Assessment of natural DNA methylation variation and its association with economically important traits in dolichos bean (Lablab purpureus L. Var. Lignosus) using AMP-PCR assay

As a prelude to exploit DNA methylation-induced variation, we hypothesized the existence of substantial natural DNA methylation variation and its association with economically important traits in dolichos bean, and tested it using amplified methylation polymorphism-polymerase chain reaction (AMP-PCR) assay. DNA methylation patterns such as internal, external, full and non-methylation were amplified in a set of 64 genotypes using 26 customized randomly amplified polymorphic DNA (RAPD) primers containing 5'CCGG3' sequence. The 64 genotypes included 60 germplasm accessions (GA), two advanced breeding lines (ABLs) and two released varieties. The ABLs and released varieties are referred to as improved germplasm accessions (IGA) in this study. The association of DNA methylation patterns with economically important traits such as days to 50% flowering, raceme length, fresh pods plant^-1, fresh pod yield plant^-1 and 100-fresh seed weight was explored. At least 50 genotypes were polymorphic for DNA methylation patterns at 10 loci generated by seven of the 26 RAPD primers. The GA and IGA differed significantly for total, full and external methylation and the frequency of methylation was higher in GA compared to that in IGA. The genotypes with external methylation produced longer racemes than those with full, internal and non-methylation in that order at polymorphic RAPD-11-242 locus. High pod yielding genotypes had significantly lower frequency of full methylation than low yielding ones. On the contrary, the genotypes that produced heavier fresh seeds harboured higher frequencies of total and externally methylated loci than those that produced lighter fresh seeds.

Methylome and transcriptome analyses of soybean response to bean pyralid larvae

BACKGROUND

Bean pyralid is one of the major leaf-feeding insects that affect soybean crops. DNA methylation can control the networks of gene expressions, and it plays an important role in responses to biotic stress. However, at present the genome-wide DNA methylation profile of the soybean resistance to bean pyralid has not been reported so far.

RESULTS

Using whole-genome bisulfite sequencing (WGBS) and RNA-sequencing (RNA-seq), we analyzed the highly resistant material (Gantai-2-2, HRK) and highly susceptible material (Wan82-178, HSK), under bean pyralid larvae feeding 0 h and 48 h, to clarify the molecular mechanism of the soybean resistance and explore its insect-resistant genes. We identified 2194, 6872, 39,704 and 40,018 differentially methylated regions (DMRs), as well as 497, 1594, 9596 and 9554 differentially methylated genes (DMGs) in the HRK0/HRK48, HSK0/HSK48, HSK0/HRK0 and HSK48/HRK48 comparisons, respectively. Through the analysis of global methylation and transcription, 265 differentially expressed genes (DEGs) were negatively correlated with DMGs, there were 34, 49, 141 and 116 negatively correlated genes in the HRK0/HRK48, HSK0/HSK48, HSK0/HRK0 and HSK48/HRK48, respectively. The MapMan cluster analysis showed that 114 negatively correlated genes were clustered in 24 pathways, such as protein biosynthesis and modification; primary metabolism; secondary metabolism; cell cycle, cell structure and component; RNA biosynthesis and processing, and so on. Moreover, CRK40; CRK62; STK; MAPK9; L-type lectin-domain containing receptor kinase VIII.2; CesA; CSI1; fimbrin-1; KIN-14B; KIN-14 N; KIN-4A; cytochrome P450 81E8; BEE1; ERF; bHLH25; bHLH79; GATA26, were likely regulatory genes involved in the soybean responses to bean pyralid larvae. Finally, 5 DMRs were further validated that the genome-wide DNA data were reliable through PS-PCR and 5 DEGs were confirmed the relationship between DNA methylation and gene expression by qRT-PCR. The results showed an excellent agreement with deep sequencing.

CONCLUSIONS

Genome-wide DNA methylation profile of soybean response to bean pyralid was obtained for the first time. Several specific DMGs which participated in protein kinase, cell and organelle, flavonoid biosynthesis and transcription factor were further identified to be likely associated with soybean response to bean pyralid. Our data will provide better understanding of DNA methylation alteration and their potential role in soybean insect resistance.

Differential DNA methylation between long-winged and short-winged adults of Nilaparvata lugens

Nilaparvata lugens, a catastrophic rice pest in South East Asia, has adults with wing dimorphism. DNA methylation has been proved to play an important role in regulation of phenotype differentiation in insects. In this study, methylation sensitive amplification polymorphism (MSAP) was used to investigate the cytosine methylation state at CCGG sites in macropterous male adults (MMA) and brachypterous male adults (BMA) of brown planthopper. In MMA, the fully methylated ratio was 2.96%, hemi-methylated ratio 3.83% and total methylated ratio 6.79%. In BMA, they were 5.53%, 4.19% and 9.72%, respectively. There were significant differences in the methylation of the target sites (CCGG) between MMA and BMA (ØST = 0.2614, P = 0.0354). Based the PCoA results, a much clear separation were also shown between MMA and BMA along the first coordinate (38.8% of variance explained). We also cloned and got nine satisfactory sequences with different methylation states between MMA and BMA. Two of them have similarity with male-specific sequence in chromosome Y and lipophorin receptor gene in N. lugens, respectively. The result showed that the methylation patterns and levels were different between two wing phenotypes of N. lugens, and will facilitate research on the epigenetic mechanism of insect wing dimorphism.

Identification of a Novel NtLRR-RLK and Biological Pathways That Contribute to Tolerance of TMV in Nicotiana tabacum

Tobacco mosaic virus (TMV) infection can causes serious damage to tobacco crops. To explore the approach of preventing TMV infection of plants, two tobacco cultivars with different resistances to TMV were used to analyze transcription profiling before and after TMV infection. The involvement of biological pathways differed between the tolerant variety (Yuyan8) and the susceptible variety (NC89). In particular, the plant-virus interaction pathway was rapidly activated in Yuyan8, and specific resistance genes were enriched. Liquid chromatography tandem mass spectrometry analysis detected large quantities of antiviral substances in the tolerant Yuyan8. A novel Nicotiana tabacum leucine-rich repeat receptor kinase (NtLRR-RLK) gene was identified as being methylated and this was verified using bisulfite sequencing. Transient expression of TMV-green fluorescent protein in pRNAi-NtLRR-RLK transgenic plants confirmed that NtLRR-RLK was important for susceptibility to TMV. The specific protein interaction map generated from our study revealed that levels of BIP1, E3 ubiquitin ligase, and LRR-RLK were significantly elevated, and all were represented at node positions in the protein interaction map. The same expression tendency of these proteins was also found in pRNAi-NtLRR-RLK transgenic plants at 24 h after TMV inoculation. These data suggested that specific genes in the infection process can activate the immune signal cascade through different resistance genes, and the integration of signal pathways could produce resistance to the virus. These results contribute to the overall understanding of the molecular basis of plant resistance to TMV and in the long term could identify new strategies for prevention and control virus infection.

Changes in DNA Methylation in Response to 6-Benzylaminopurine Affect Allele-Specific Gene Expression in Populus Tomentosa

Cytokinins play important roles in the growth and development of plants. Physiological and photosynthetic characteristics are common indicators to measure the growth and development in plants. However, few reports have described the molecular mechanisms of physiological and photosynthetic changes in response to cytokinin, particularly in woody plants. DNA methylation is an essential epigenetic modification that dynamically regulates gene expression in response to the external environment. In this study, we examined genome-wide DNA methylation variation and transcriptional variation in poplar (Populus tomentosa) after short-term treatment with the synthetic cytokinin 6-benzylaminopurine (6-BA). We identified 460 significantly differentially methylated regions (DMRs) in response to 6-BA treatment. Transcriptome analysis showed that 339 protein-coding genes, 262 long non-coding RNAs (lncRNAs), and 15,793 24-nt small interfering RNAs (siRNAs) were differentially expressed under 6-BA treatment. Among these, 79% were differentially expressed between alleles in P. tomentosa, and 102,819 allele-specific expression (ASE) loci in 19,200 genes were detected showing differences in ASE levels after 6-BA treatment. Combined DNA methylation and gene expression analysis demonstrated that DNA methylation plays an important role in regulating allele-specific gene expression. To further investigate the relationship between these 6-BA-responsive genes and phenotypic variation, we performed SNP analysis of 460 6-BA-responsive DMRs via re-sequencing using a natural population of P. tomentosa, and we identified 206 SNPs that were significantly associated with growth and wood properties. Association analysis indicated that 53% of loci with allele-specific expression had primarily dominant effects on poplar traits. Our comprehensive analyses of P. tomentosa DNA methylation and the regulation of allele-specific gene expression suggest that DNA methylation is an important regulator of imbalanced expression between allelic loci.

DNA Methylation Changes Induced by Cold in Psychrophilic and Psychrotolerant Naganishia Yeast Species

The involvement of DNA methylation in the response to cold stress of two different yeast species (Naganishia antarctica, psychrophilic, and Naganishia albida, psychrotolerant), exhibiting different temperature aptitudes, has been studied. Consecutive incubations at respective optimum temperatures, at 4 °C (cold stress) and at optimum temperatures again, were performed. After Methylation Sensitive Amplified Polymorphism (MSAP) fingerprints a total of 550 and 423 clear and reproducible fragments were amplified from N. antarctica and N. albida strains, respectively. The two Naganishia strains showed a different response in terms of level of DNA methylation during cold stress and recovery from cold stress. The percentage of total methylated fragments in psychrophilic N. antarctica did not show any significant change. On the contrary, the methylation of psychrotolerant N. albida exhibited a nonsignificant increase during the incubation at 4 °C and continued during the recovery step, showing a significant difference if compared with control condition, resembling an uncontrolled response to cold stress. A total of 12 polymorphic fragments were selected, cloned, and sequenced. Four fragments were associated to genes encoding for elongation factor G and for chitin synthase export chaperon. To the best of our knowledge, this is the first study on DNA methylation in the response to cold stress carried out by comparing a psychrophilic and a psychrotolerant yeast species.

DNA Methylation Profile of β-1,3-Glucanase and Chitinase Genes in Flax Shows Specificity Towards Fusarium Oxysporum Strains Differing in Pathogenicity

Most losses in flax (Linum usitatissimum L.) crops are caused by fungal infections. The new epigenetic approach to improve plant resistance requires broadening the knowledge about the influence of pathogenic and non-pathogenic Fusarium oxysporum strains on changes in the profile of DNA methylation. Two contrasting effects on the levels of methylation in flax have been detected for both types of Fusarium strain infection: Genome-wide hypermethylation and hypomethylation of resistance-related genes (β-1,3-glucanase and chitinase). Despite the differences in methylation profile, the expression of these genes increased. Plants pretreated with the non-pathogenic strain memorize the hypomethylation pattern and then react more efficiently upon pathogen infection. The peak of demethylation correlates with the alteration in gene expression induced by the non-pathogenic strain. In the case of pathogen infection, the expression peak lags behind the gene demethylation. Dynamic changes in tetramer methylation induced by both pathogenic and non-pathogenic Fusarium strains are dependent on the ratio between the level of methyltransferase and demethylase gene expression. Infection with both Fusarium strains suppressed methyltransferase expression and increased the demethylase (demeter) transcript level. The obtained results provide important new information about changes in methylation profile and thus expression regulation of pathogenesis-related genes in the flax plant response to stressors.

Physiological, epigenetic and genetic regulation in some olive cultivars under salt stress

Cultivated olive, a typical fruit crop species of the semi-arid regions, could successfully face the new scenarios driven by the climate change through the selection of tolerant varieties to salt and drought stresses. In the present work, multidisciplinary approaches, including physiological, epigenetic and genetic studies, have been applied to clarify the salt tolerance mechanisms in olive. Four varieties (Koroneiki, Royal de Cazorla, Arbequina and Picual) and a related form (O. europaea subsp. cuspidata) were grown in a hydroponic system under different salt concentrations from zero to 200 mM. In order to verify the plant response under salt stress, photosynthesis, gas exchange and relative water content were measured at different time points, whereas chlorophyll and leaf concentration of Na+, K+ and Ca2+ ions, were quantified at 43 and 60 days after treatment, when stress symptoms became prominent. Methylation sensitive amplification polymorphism (MSAP) technique was used to assess the effects of salt stress on plant DNA methylation. Several fragments resulted differentially methylated among genotypes, treatments and time points. Real time quantitative PCR (RT-qPCR) analysis revealed significant expression changes related to plant response to salinity. Four genes (OePIP1.1, OePetD, OePI4Kg4 and OeXyla) were identified, as well as multiple retrotransposon elements usually targeted by methylation under stress conditions.

The contrasting response to drought and waterlogging is underpinned by divergent DNA methylation programs associated with transcript accumulation in sesame

DNA methylation is a heritable epigenetic mechanism that participates in gene regulation under abiotic stresses in plants. Sesame (Sesamum indicum) is typically considered a drought-tolerant crop but highly susceptible to waterlogging, probably because of its origin in Africa or India. Understanding DNA methylation patterns under drought and waterlogging conditions can provide insights into the regulatory mechanisms underlying sesame contrasting responses to these abiotic stresses. We combined Methylation-Sensitive Amplified Polymorphism and transcriptome analyses to profile cytosine methylation patterns, transcript accumulation, and their interplay in drought-tolerant and waterlogging-tolerant sesame genotypes. Drought stress strongly induced de novo methylation (DNM) whereas most of the loci were demethylated (DM) during the recovery phase. In contrast, waterlogging stress decreased the level of methylation but during the recovery phase, both DM and DNM were concomitantly deployed. In both stresses, the levels of the differentially accumulated transcripts (DATs) highly correlated with the methylation patterns. We observed that DM was associated with an increase of DAT levels while DNM was correlated with a decrease of DAT levels. Altogether, sesame has divergent epigenetic programs that respond to drought and waterlogging stresses and an interplay among DNA methylation and transcript accumulation may partly modulate the contrasting responses to these stresses.

Genome-wide DNA methylation analysis of the regenerative and non-regenerative tissues in sika deer (Cervus nippon)

Deer antlers, the secondary organs of deer, are a unique model to study regeneration of organ/tissue in mammals. Pedicle periosteum (PP) is the key tissue type for antler regeneration. Based on our previous study, the DNA methylation was found to be the basic molecular mechanism underlying the antler regeneration. In this study, we compare the genome-wide DNA methylation level in regenerative tissues (the potentiated PP of antler, muscle, heart and liver) and non-regenerative tissue (the dormant PP) of deer by the fluorescence-labeled methylation-sensitive amplified polymorphism (F-MSAP) method. Our results showed that DNA methylation level was significantly lower in the regenerative tissues compared to the non-regenerative tissue (P < 0.05). Furthermore, 26 T-DMRs which displayed different methylated status in regenerative and non-regenerative tissues were identified by the MSAP method, and were further confirmed by Southern blot analysis. Taken together, our data suggest that DNA methylation, an important epigenetic regulation mechanism, may play an important role in the mammalian tissue/organ regeneration.

Genome-wide epigenetic variation among ash trees differing in susceptibility to a fungal disease

Background

European ash trees (Fraxinus excelsior) are currently threatened by ash dieback (ADB) caused by the fungus Hymenoscyphus fraxineus but a small percentage of the population possesses natural low susceptibility. The genome of a European ash tree has recently been sequenced. Here, we present whole genome DNA methylation data for two F. excelsior genotypes with high susceptibility to ADB, and two genotypes with low susceptibility, each clonally replicated. We also include two genotypes of Manchurian ash (F. mandshurica), an ash species which has co-evolved with H. fraxineus and also has low susceptibility to ADB.

Results

In F. excelsior, we find an average methylation level of 76.2% in the CG context, 52.0% in the CHG context, and 13.9% in the CHH context; similar levels to those of tomato. We find higher methylation in transposable elements as opposed to non-mobile elements, and high densities of Non-Differentially Methylation Positions (N-DMPs) in genes with housekeeping functions. Of genes putatively duplicated in whole genome duplication (WGD) events, an average of 25.9% are differentially methylated in at least one cytosine context, potentially indicative of unequal silencing. Variability in methylation patterns exists among clonal replicates, and this is only slightly less than the variability found between different genotypes. Of twenty genes previously found to have expression levels associated with ADB susceptibility, we find only two of these have differential methylation between high and low susceptibility F. excelsior trees. In addition, we identify 1683 significant Differentially Methylated Regions (DMRs) (q-value< 0.001) between the high and low susceptibility genotypes of F. excelsior trees, of which 665 remain significant when F. mandshurica samples are added to the low susceptibility group.

Conclusions

We find a higher frequency of differentially methylated WGD-derived gene duplicates in ash than other plant species previously studied. We also identify a set of genes with differential methylation between genotypes and species with high versus low susceptibility to ADB. This provides valuable foundational data for future work on the role that epigenetics may play in gene dosage compensation and susceptibility to ADB in ash.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4874-8) contains supplementary material, which is available to authorized users.

Compositional shifts in root-associated bacterial and archaeal microbiota track the plant life cycle in field-grown rice

Bacterial communities associated with roots impact the health and nutrition of the host plant. The dynamics of these microbial assemblies over the plant life cycle are, however, not well understood. Here, we use dense temporal sampling of 1,510 samples from root spatial compartments to characterize the bacterial and archaeal components of the root-associated microbiota of field grown rice (Oryza sativa) over the course of 3 consecutive growing seasons, as well as 2 sites in diverse geographic regions. The root microbiota was found to be highly dynamic during the vegetative phase of plant growth and then stabilized compositionally for the remainder of the life cycle. Bacterial and archaeal taxa conserved between field sites were defined as predictive features of rice plant age by modeling using a random forest approach. The age-prediction models revealed that drought-stressed plants have developmentally immature microbiota compared to unstressed plants. Further, by using genotypes with varying developmental rates, we show that shifts in the microbiome are correlated with rates of developmental transitions rather than age alone, such that different microbiota compositions reflect juvenile and adult life stages. These results suggest a model for successional dynamics of the root-associated microbiota over the plant life cycle.

Plant roots are colonized by complex communities of bacterial and archaeal microbiota from the soil, with the potential to affect plant nutrition and fitness. Although root-associated microbes are known to have the potential to be utilized to promote crop productivity, their exploitation has been hindered by a lack of understanding of the compositional dynamics of these communities. Here we investigate temporal changes in the root-associated bacterial and archaeal communities throughout the plant life cycle in field-grown rice over multiple seasons and locations. Our results indicate that root microbiota composition varies with both chronological age and the developmental stage of the plants. We find that a major compositional shift correlates with the transition to reproductive growth, suggestive of distinct root microbiota associations for the juvenile and adult plant phases. The results from this study highlight dynamic relationships between plant growth and associated microbiota that should be considered in strategies for the successful manipulation of microbial communities to enhance crop performance.

Genome-wide analysis of DNA methylation in five tissues of sika deer (Cervus nippon)

DNA methylation plays an important role in regulating gene expression during tissue development and differentiation in eukaryotes. In contrast to domestic animals, epigenetic studies have been seldom conducted in wild animals. In the present study, we conducted the genome-wide profiling of DNA methylation for five tissues of sika deer using the fluorescence-labeled methylation-sensitive amplified polymorphism (F-MSAP) technique. Overall, a total of 104,131 fragments were amplified including 41,951 methylated fragments using 32 pairs of selected primers. The average incidence of DNA methylation was approximately 38.18% in muscle, 40.32% in heart, 41.86% in liver, 41.20% in lung, and 41.68% in kidney, respectively. Also, the significant differences of the DNA methylation levels were found between the different tissue types (P<0.05), which indicates that the differences of genome-wide DNA methylation levels may be related to gene expression during tissue development and differentiation. In addition, 37 tissue-specific differentially methylated regions (T-DMRs) were identified and recovered by MSAP in five tissues, and were further confirmed by Southern blot analysis. Our study presents the first look at the T-DMRs in sika deer and represents an initial step towards understanding of epigenetic regulatory mechanism underlying tissue development and differentiation in sika deer.

Changes in the DNA methylation pattern of the host male gametophyte of viroid-infected cucumber plants

Eukaryotic organisms exposed to adverse conditions are required to show a certain degree of transcriptional plasticity in order to cope successfully with stress. Epigenetic regulation of the genome is a key regulatory mechanism allowing dynamic changes of the transcriptional status of the plant in response to stress. The Hop stunt viroid (HSVd) induces the demethylation of ribosomal RNA (rRNA) in cucumber (Cucumis sativus) leaves, leading to increasing transcription rates of rRNA. In addition to the clear alterations observed in vegetative tissues, HSVd infection is also associated with drastic changes in gametophyte development. To examine the basis of viroid-induced alterations in reproductive tissues, we analysed the cellular and molecular consequences of HSVd infection in the male gametophyte of cucumber plants. Our results indicate that in the pollen grain, accumulation of HSVd RNA induces a decondensation of the generative nucleus that correlates with a dynamic demethylation of repetitive regions in the cucumber genome that include rRNA genes and transposable elements (TEs). We therefore propose that HSVd infection impairs the epigenetic control of rRNA genes and TEs in gametic cells of cucumber, a phenomenon thus far unknown to occur in this reproductive tissue as a consequence of pathogen infection.

Stable methylation of a non-coding RNA gene regulates gene expression in response to abiotic stress in Populus simonii

DNA methylation plays important roles in responses to environmental stimuli. However, in perennial plants, the roles of DNA methylation in stress-specific adaptions to different abiotic stresses remain unclear. Here, we present a systematic, comparative analysis of the methylome and gene expression in poplar under cold, osmotic, heat, and salt stress conditions from 3h to 24h. Comparison of the stress responses revealed different patterns of cytosine methylation in response to the four abiotic stresses. We isolated and sequenced 1376 stress-specific differentially methylated regions (SDMRs); annotation revealed that these SDMRs represent 1123 genes encoding proteins, 16 miRNA genes, and 17 long non-coding RNA (lncRNA) genes. The SDMR162 region, consisting of Psi-MIR396e and PsiLNCRNA00268512, is regulated by epigenetic pathways and we speculate that PsiLNCRNA00268512 regulates miR396e levels by acting as a target mimic. The ratios of methylated cytosine declined to ~35.1% after 1 month of recovery from abiotic stress and to ~15.3% after 6 months. Among methylated miRNA genes, only expression of the methylation-regulated gene MIRNA6445a showed long-term stability. Our data provide a strong basis for future work and improve our understanding of the effect of epigenetic regulation of non-coding RNA expression, which will enable in-depth functional analysis.

Methylation of miRNA genes in the response to temperature stress in Populus simonii

DNA methylation and miRNAs provide crucial regulation of the transcriptional and post-transcriptional responses to abiotic stress. In this study, we used methylation-sensitive amplification polymorphisms to identify 1066 sites that were differentially methylated in response to temperature stress in Populus simonii. Among these loci, BLAST searches of miRBase identified seven miRNA genes. Expression analysis by quantitative real-time PCR suggested that the methylation pattern of these miRNA genes probably influences their expression. Annotation of these miRNA genes in the sequenced genome of Populus trichocarpa found three target genes (Potri.007G090400, Potri.014G042200, and Potri.010G176000) for the miRNAs produced from five genes (Ptc-MIR396e and g, Ptc-MIR156i and j, and Ptc-MIR390c) respectively. The products of these target genes function in lipid metabolism to deplete lipid peroxide. We also constructed a network based on the interactions between DNA methylation and miRNAs, miRNAs and target genes, and the products of target genes and the metabolic factors that they affect, including H2O2, malondialdehyde, catalase (CAT), and superoxide dismutase. Our results suggested that DNA methylation probably regulates the expression of miRNA genes, thus affecting expression of their target genes, likely through the gene-silencing function of miRNAs, to maintain cell survival under abiotic stress conditions.

Inheritance and variation of Cytosine methylation in three populus allotriploid populations with different heterozygosity

DNA methylation is an epigenetic mechanism with the potential to regulate gene expression and affect plant phenotypes. Both hybridization and genome doubling may affect the DNA methylation status of newly formed allopolyploid plants. Previous studies demonstrated that changes in cytosine methylation levels and patterns were different among individual hybrid plant, therefore, studies investigating the characteristics of variation in cytosine methylation status must be conducted at the population level to avoid sampling error. In the present study, an F1 hybrid diploid population and three allotriploid populations with different heterozygosity [originating from first-division restitution (FDR), second-division restitution (SDR), and post-meiotic restitution (PMR) 2n eggs of the same female parent] were used to investigate cytosine methylation inheritance and variation relative to their common parents using methylation-sensitive amplification polymorphism (MSAP). The variation in cytosine methylation in individuals in each population exhibited substantial differences, confirming the necessity of population epigenetics. The total methylation levels of the diploid population were significantly higher than in the parents, but those of the three allotriploid populations were significantly lower than in the parents, indicating that both hybridization and polyploidization contributed to cytosine methylation variation. The vast majority of methylated status could be inherited from the parents, and the average percentages of non-additive variation were 6.29, 3.27, 5.49 and 5.07% in the diploid, FDR, SDR and PMR progeny populations, respectively. This study lays a foundation for further research on population epigenetics in allopolyploids.

DNA methylation and transcriptomic changes in response to different lights and stresses in 7B-1 male-sterile tomato

We reported earlier that 7B-1 mutant in tomato (Solanum lycopersicum L., cv. Rutgers), an ABA overproducer, is defective in blue light (B) signaling leading to B-specific resistance to abiotic and biotic stresses. Using a methylation-sensitive amplified polymorphism (MSAP) assay, a number of genes were identified, which were differentially methylated between 7B-1 and its wild type (WT) seedlings in white (W), blue (B), red (R) lights and dark (D) or in response to exogenous ABA and mannitol-induced stresses. The genomic methylation level was almost similar in different lights between 7B-1 and WT seedlings, while significant differences were observed in response to stresses in D, but not B. Using a cDNA-AFLP assay, several transcripts were identified, which were differentially regulated between 7B-1 and WT by B or D or in response to stresses. Blue light receptors cryptochrome 1 and 2 (CRY1 and CRY2) and phototropin 1 and 2 (PHOT1 and PHOT2) were not affected by the 7B-1 mutation at the transcriptional level, instead the mutation had likely affected downstream components of the light signaling pathway. 5-azacytidine (5-azaC) induced DNA hypomethylation, inhibited stem elongation and differentially regulated the expression of a number of genes in 7B-1. In addition, it was shown that mir167 and mir390 were tightly linked to auxin signaling pathway in 5-azaC-treated 7B-1 seedlings via the regulation of auxin-response factor (ARF) transcripts. Our data showed that DNA methylation remodeling is an active epigenetic response to different lights and stresses in 7B-1 and WT, and highlighted the differences in epigenetic and transcriptional regulation of light and stress responses between 7B-1 and WT. Furthermore, it shed lights on the crosstalk between DNA hypomethylation and miRNA regulation of ARFs expression. This information could also be used as a benchmark for future studies of male-sterility in other crops.

Epi-fingerprinting and epi-interventions for improved crop production and food quality

Increasing crop production at a time of rapid climate change represents the greatest challenge facing contemporary agricultural research. Our understanding of the genetic control of yield derives from controlled field experiments designed to minimize environmental variance. In spite of these efforts there is substantial residual variability among plants attributable to Genotype × Environment interactions. Recent advances in the field of epigenetics have revealed a plethora of gene control mechanisms that could account for much of this unassigned variation. These systems act as a regulatory interface between the perception of the environment and associated alterations in gene expression. Direct intervention of epigenetic control systems hold the enticing promise of creating new sources of variability that could enhance crop performance. Equally, understanding the relationship between various epigenetic states and responses of the crop to specific aspects of the growing environment (epigenetic fingerprinting) could allow for a more tailored approach to plant agronomy. In this review, we explore the many ways in which epigenetic interventions and epigenetic fingerprinting can be deployed for the improvement of crop production and quality.

Iron deficiency in barley plants: phytosiderophore release, iron translocation, and DNA methylation

All living organisms require iron (Fe) to carry out many crucial metabolic pathways. Despite its high concentrations in the geosphere, Fe bio-availability to plant roots can be very scarce. To cope with Fe shortage, plants can activate different strategies. For these reasons, we investigated Fe deficient Hordeum vulgare L. plants by monitoring growth, phytosiderophores (PS) release, iron content, and translocation, and DNA methylation, with respect to Fe sufficient ones. Reductions of plant growth, roots to shoots Fe translocation, and increases in PS release were found. Experiments on DNA methylation highlighted significant differences between fully and hemy-methylated sequences in Fe deficient plants, with respect to Fe sufficient plants. Eleven DNA bands differently methylated were found in starved plants. Of these, five sequences showed significant alignment to barley genes encoding for a glucosyltransferase, a putative acyl carrier protein, a peroxidase, a β-glucosidase and a transcription factor containing a Homeodomin. A resupply experiment was carried out on starved barley re-fed at 13 days after sowing (DAS), and it showed that plants did not recover after Fe addition. In fact, Fe absorption and root to shoot translocation capacities were impaired. In addition, resupplied barley showed DNA methylation/demethylation patterns very similar to that of barley grown in Fe deprivation. This last finding is very encouraging because it indicates as these variations/modifications could be transmitted to progenies.

Limited DNA methylation variation and the transcription of MET1 and DDM1 in the genus Chrysanthemum (Asteraceae): following the track of polyploidy

Polyploidy has been recognized as a widespread and common phenomenon among flowering plants. DNA-5'-CCGG site cytosine methylation (C-methylation) is one of the major and immediate epigenetic responses of the plant genome. Elucidating the ways in which altered C-methylation patterns, either at the whole genomic level or at specific sites can affect genome stability in polyploidy will require substantial additional investigation. Methylation sensitive amplification polymorphism profiling was used to evaluate variation in C-methylation among a set of 20 Chrysanthemum species and their close relatives of varying ploidy levels from diploid to decaploid. The range in relative C-methylation level was within 10%, and there was no significant difference neither between different ploidy levels nor between different species in the same ploidy level (U-values < 1.96). The transcript abundances of MET1 and DDM1 genes, which both involved in the regulation of C-methylation at CpG sites, were enhanced with increased ploidy level, but only MET1 was positively correlated with the nuclear DNA content. Considering the key role and efficiency of MET1 in maintaining CpG methylation, the limited variation observed with respect to C-methylation may reflect a balance between the increased activity of MET1 in the higher ploidy genomes and the larger number of CpG dinucleotide sites available for methylation.

Characterization of in vitro haploid and doubled haploid Chrysanthemum morifolium plants via unfertilized ovule culture for phenotypical traits and DNA methylation pattern

Chrysanthemum is one of important ornamental species in the world. Its highly heterozygous state complicates molecular analysis, so it is of interest to derive haploid forms. A total of 2579 non-fertilized chrysanthemum ovules pollinated by Argyranthemum frutescens were cultured in vitro to isolate haploid progeny. One single regenerant emerged from each of three of the 105 calli produced. Chromosome counts and microsatellite fingerprinting showed that only one of the regenerants was a true haploid. Nine doubled haploid derivatives were subsequently generated by colchicine treatment of 80 in vitro cultured haploid nodal segments. Morphological screening showed that the haploid plant was shorter than the doubled haploids, and developed smaller leaves, flowers, and stomata. An in vitro pollen germination test showed that few of the haploid's pollen were able to germinate and those which did so were abnormal. Both the haploid and the doubled haploids produced yellow flowers, whereas those of the maternal parental cultivar were mauve. Methylation-sensitive amplification polymorphism (MSAP) profiling was further used to detect alterations in cytosine methylation caused by the haploidization and/or the chromosome doubling processes. While 52.2% of the resulting amplified fragments were cytosine methylated in the maternal parent's genome, the corresponding proportions for the haploid's and doubled haploids' genomes were, respectively, 47.0 and 51.7%, demonstrating a reduction in global cytosine methylation caused by haploidization and a partial recovery following chromosome doubling.

DNA methylation levels analysis in four tissues of sea cucumber Apostichopus japonicus based on fluorescence-labeled methylation-sensitive amplified polymorphism (F-MSAP) during aestivation

DNA methylation plays an important role in regulating transcriptional change in response to environmental stimuli. In the present study, DNA methylation levels of tissues of the sea cucumber Apostichopus japonicus were analyzed by the fluorescence-labeled methylation-sensitive amplified polymorphism (F-MSAP) technique over three stages of the aestivation cycle. Overall, a total of 26,963 fragments were amplified including 9112 methylated fragments among four sea cucumber tissues using 18 pairs of selective primers. Results indicated an average DNA methylation level of 33.79% for A. japonicus. The incidence of DNA methylation was different across tissue types in the non-aestivation stage: intestine (30.16%), respiratory tree (27.61%), muscle (27.94%) and body wall (56.25%). Our results show that hypermethylation accompanied deep-aestivation in A. japonicus, which suggests that DNA methylation may have an important role in regulating global transcriptional suppression during aestivation. Further analysis indicated that the main DNA modification sites were focused on intestine and respiratory tree tissues and that full-methylation but not hemi-methylation levels exhibited significant increases in the deep-aestivation stage.

Roles, and establishment, maintenance and erasing of the epigenetic cytosine methylation marks in plants

Heritable information in plants consists of genomic information in DNA sequence and epigenetic information superimposed on DNA sequence. The latter is in the form of cytosine methylation at CG, CHG and CHH elements (where H = A, T orC) and a variety of histone modifications in nucleosomes. The epialleles arising from cytosine methylation marks on the nuclear genomic loci have better heritability than the epiallelic variation due to chromatin marks. Phenotypic variation is increased manifold by epiallele comprised methylomes. Plants (angiosperms) have highly conserved genetic mechanisms to establish, maintain or erase cytosine methylation from epialleles. The methylation marks in plants fluctuate according to the cell/tissue/organ in the vegetative and reproductive phases of plant life cycle. They also change according to environment. Epialleles arise by gain or loss of cytosine methylation marks on genes. The changes occur due to the imperfection of the processes that establish and maintain the marks and on account of spontaneous and stress imposed removal of marks. Cytosine methylation pattern acquired in response to abiotic or biotic stress is often inherited over one to several subsequent generations.Cytosine methylation marks affect physiological functions of plants via their effect(s) on gene expression levels. They also repress transposable elements that are abundantly present in plant genomes. The density of their distribution along chromosome lengths affects meiotic recombination rate, while their removal increases mutation rate. Transposon activation due to loss of methylation causes rearrangements such that new gene regulatory networks arise and genes for microRNAs may originate. Cytosine methylation dynamics contribute to evolutionary changes. This review presents and discusses the available evidence on origin, removal and roles of cytosine methylation and on related processes, such as RNA directed DNA methylation, imprinting, paramutation and transgenerational memory in plants.

Pleiotropic phenotypes of the salt-tolerant and cytosine hypomethylated leafless inflorescence, evergreen dwarf and irregular leaf lamina mutants of Catharanthus roseus possessing Mendelian inheritance

In Catharanthus roseus, three morphological cum salt-tolerant chemically induced mutants of Mendelian inheritance and their wild-type parent cv Nirmal were characterized for overall cytosine methylation at DNA repeats, expression of 119 protein coding and seven miRNA-coding genes and 50 quantitative traits. The mutants, named after their principal morphological feature(s), were leafless inflorescence (lli), evergreen dwarf (egd) and irregular leaf lamina (ill). The Southern-blot analysis of MspI digested DNAs of mutants probed with centromeric and 5S and 18S rDNA probes indicated that, in comparison to wild type, the mutants were extensively demethylated at cytosine sites. Among the 126 genes investigated for transcriptional expression, 85 were upregulated and 41 were downregulated in mutants. All of the five genes known to be stress responsive had increased expression in mutants. Several miRNA genes showed either increased or decreased expression in mutants. The C. roseus counterparts of CMT3, DRM2 and RDR2 were downregulated in mutants. Among the cell, organ and plant size, photosynthesis and metabolism related traits studied, 28 traits were similarly affected in mutants as compared to wild type. Each of the mutants also expressed some traits distinctively. The egd mutant possessed superior photosynthesis and water retention abilities. Biomass was hyperaccumulated in roots, stems, leaves and seeds of the lli mutant. The ill mutant was richest in the pharmaceutical alkaloids catharanthine, vindoline, vincristine and vinblastine. The nature of mutations, origins of mutant phenotypes and evolutionary importance of these mutants are discussed.

Cytoplasmic effects on DNA methylation between male sterile lines and the maintainer in wheat (Triticum aestivum L.)

Male sterile cytoplasm plays an important role in hybrid wheat, and three-line system including male sterile (A line), its maintainer (B line) and restoring (R line) has played a major role in wheat hybrid production. It is well known that DNA methylation plays an important role in gene expression regulation during biological development in wheat. However, no reports are available on DNA methylation affected by different male sterile cytoplasms in hybrid wheat. We employed a methylation-sensitive amplified polymorphism technique to characterize nuclear DNA methylation in three male sterile cytoplasms. A and B lines share the same nucleus, but have different cytoplasms which is male sterile for the A and fertile for the B. The results revealed a relationship of DNA methylation at these sites specifically with male sterile cytoplasms, as well as male sterility, since the only difference between the A lines and B line was the cytoplasm. The DNA methylation was markedly affected by male sterile cytoplasms. K-type cytoplasm affected the methylation to a much greater degree than T-type and S-type cytoplasms, as indicated by the ratio of methylated sites, ratio of fully methylated sites, and polymorphism between A lines and B line for these cytoplasms. The genetic distance between the cytoplasm and nucleus for the K-type is much greater than for the T- and S-types because the former is between Aegilops genus and Triticum genus and the latter is within Triticum genus between Triticum spelta and Triticum timopheevii species. Thus, this difference in genetic distance may be responsible for the variation in methylation that we observed.

Transgenerational variations in DNA methylation induced by drought stress in two rice varieties with distinguished difference to drought resistance

Adverse environmental conditions have large impacts on plant growth and crop production. One of the crucial mechanisms that plants use in variable and stressful natural environments is gene expression modulation through epigenetic modification. In this study, two rice varieties with different drought resistance levels were cultivated under drought stress from tilling stage to seed filling stage for six successive generations. The variations in DNA methylation of the original generation (G0) and the sixth generation (G6) of these two varieties in normal condition (CK) and under drought stress (DT) at seedling stage were assessed by using Methylation Sensitive Amplification Polymorphism (MSAP) method. The results revealed that drought stress had a cumulative effect on the DNA methylation pattern of both varieties, but these two varieties had different responses to drought stress in DNA methylation. The DNA methylation levels of II-32B (sensitive) and Huhan-3 (resistant) were around 39% and 32%, respectively. Genome-wide DNA methylation variations among generations or treatments accounted for around 13.1% of total MSAP loci in II-32B, but was only approximately 1.3% in Huhan-3. In II-32B, 27.6% of total differentially methylated loci (DML) were directly induced by drought stress and 3.2% of total DML stably transmitted their changed DNA methylation status to the next generation. In Huhan-3, the numbers were 48.8% and 29.8%, respectively. Therefore, entrainment had greater effect on Huhan-3 than on II-32B. Sequence analysis revealed that the DML were widely distributed on all 12 rice chromosomes and that it mainly occurred on the gene’s promoter and exon region. Some genes with DML respond to environmental stresses. The inheritance of epigenetic variations induced by drought stress may provide a new way to develop drought resistant rice varieties.

A pathogenic non-coding RNA induces changes in dynamic DNA methylation of ribosomal RNA genes in host plants

Viroids are plant-pathogenic non-coding RNAs able to interfere with as yet poorly known host-regulatory pathways and to cause alterations recognized as diseases. The way in which these RNAs coerce the host to express symptoms remains to be totally deciphered. In recent years, diverse studies have proposed a close interplay between viroid-induced pathogenesis and RNA silencing, supporting the belief that viroid-derived small RNAs mediate the post-transcriptional cleavage of endogenous mRNAs by acting as elicitors of symptoms expression. Although the evidence supporting the role of viroid-derived small RNAs in pathogenesis is robust, the possibility that this phenomenon can be a more complex process, also involving viroid-induced alterations in plant gene expression at transcriptional levels, has been considered. Here we show that plants infected with the ‘Hop stunt viroid’ accumulate high levels of sRNAs derived from ribosomal transcripts. This effect was correlated with an increase in the transcription of ribosomal RNA (rRNA) precursors during infection. We observed that the transcriptional reactivation of rRNA genes correlates with a modification of DNA methylation in their promoter region and revealed that some rRNA genes are demethylated and transcriptionally reactivated during infection. This study reports a previously unknown mechanism associated with viroid (or any other pathogenic RNA) infection in plants providing new insights into aspects of host alterations induced by the viroid infectious cycle.

Do transgenesis and marker-assisted backcross breeding produce substantially equivalent plants? A comparative study of transgenic and backcross rice carrying bacterial blight resistant gene Xa21

Background

The potential impact of genetically modified (GM) plants on human health has attracted much attention worldwide, and the issue remains controversial. This is in sharp contrast to the broad acceptance of plants produced by breeding through Marker Assisted Backcrossing (MAB).

Results

Focusing on transcriptome variation and perturbation to signaling pathways, we assessed the molecular and biological aspects of substantial equivalence, a general principle for food safety endorsed by the Food and Agricultural Organization and the World Health Organization, between a transgenic crop and a plant from MAB breeding. We compared a transgenic rice line (DXT) and a MAB rice line (DXB), both of which contain the gene Xa21 providing resistance to bacterial leaf blight. By using Next-Generation sequencing data of DXT, DXB and their parental line (D62B), we compared the transcriptome variation of DXT and DXB. Remarkably, DXT had 43% fewer differentially expressed genes (DEGs) than DXB. The genes exclusively expressed in DXT and in DXB have pathogen and stress defense functions. Functional categories of DEGs in DXT were comparable to that in DXB, and seven of the eleven pathways significantly affected by transgenesis were also perturbed by MAB breeding.

Conclusions

These results indicated that the transgenic rice and rice from MAB breeding are substantial equivalent at the transcriptome level, and paved a way for further study of transgenic rice, e.g., understanding the chemical and nutritional properties of the DEGs identified in the current study.

Ecological Epigenetics: Beyond MS-AFLP

Ecological Epigenetics studies the relationship between epigenetic variation and ecologically relevant phenotypic variation. As molecular epigenetic mechanisms often control gene expression, even across generations, they may impact many evolutionary processes. Multiple molecular epigenetic mechanisms exist, but methylation of DNA so far has dominated the Ecological Epigenetic literature. There are several molecular techniques used to screen methylation of DNA; here, we focus on the most common technique, methylation-sensitive-AFLP (MS-AFLP), which is used to identify genome-wide methylation patterns. We review studies that used MS-AFLP to address ecological questions, that describe which taxa have been investigated, and that identify general trends in the field. We then discuss, noting the general themes, four studies across taxa that demonstrate characteristics that increase the inferences that can be made from MS-AFLP data; we suggest that future MS-AFLP studies should incorporate these methods and techniques. We then review the short-comings of MS-AFLP and suggest alternative techniques that might address some of these limitations. Finally, we make specific suggestions for future research on MS-AFLP and identify questions that are most compelling and tractable in the short term.

Cytosine methylation alteration in natural populations of Leymus chinensis induced by multiple abiotic stresses

Background

Human activity has a profound effect on the global environment and caused frequent occurrence of climatic fluctuations. To survive, plants need to adapt to the changing environmental conditions through altering their morphological and physiological traits. One known mechanism for phenotypic innovation to be achieved is environment-induced rapid yet inheritable epigenetic changes. Therefore, the use of molecular techniques to address the epigenetic mechanisms underpinning stress adaptation in plants is an important and challenging topic in biological research. In this study, we investigated the impact of warming, nitrogen (N) addition, and warming+nitrogen (N) addition stresses on the cytosine methylation status of Leymus chinensis Tzvel. at the population level by using the amplified fragment length polymorphism (AFLP), methylation-sensitive amplified polymorphism (MSAP) and retrotransposon based sequence-specific amplification polymorphism (SSAP) techniques.

Methodology/Principal Findings

Our results showed that, although the percentages of cytosine methylation changes in SSAP are significantly higher than those in MSAP, all the treatment groups showed similar alteration patterns of hypermethylation and hypomethylation. It meant that the abiotic stresses have induced the alterations in cytosine methylation patterns, and the levels of cytosine methylation changes around the transposable element are higher than the other genomic regions. In addition, the identification and analysis of differentially methylated loci (DML) indicated that the abiotic stresses have also caused targeted methylation changes at specific loci and these DML might have contributed to the capability of plants in adaptation to the abiotic stresses.

Conclusions/Significance

Our results demonstrated that abiotic stresses related to global warming and nitrogen deposition readily evoke alterations of cytosine methylation, and which may provide a molecular basis for rapid adaptation by the affected plant populations to the changed environments.

Molecular and phenotypic characterization of seedling and adult plant leaf rust resistance in a world wheat collection

Genetic resistance is the most effective approach to managing wheat leaf rust. The aim of this study was to characterize seedling and adult plant leaf rust resistance of a world wheat collection. Using controlled inoculation with ten races of Puccinia triticina, 14 seedling resistance genes were determined or postulated to be present in the collection. Lr1, Lr3, Lr10 and Lr20 were the most prevalent genes around the world while Lr9, Lr14b, Lr3ka and/or Lr30 and Lr26 were rare. To confirm some gene postulations, the collection was screened with gene-specific molecular markers for Lr1, Lr10, Lr21 and Lr34. Although possessing the Lr1 and/or Lr10 gene-specific marker, 51 accessions showed unexpected high infection types to P. triticina race BBBD. The collection was tested in the field, where rust resistance ranged from nearly immune or highly resistant with severity of 1 % and resistant host response to highly susceptible with severity of 84 % and susceptible host response. The majority of the accessions possessing the adult plant resistance (APR) gene Lr34 had a maximum rust severity of 0-35 %, similar to or better than accession RL6058, a Thatcher-Lr34 near-isogenic line. Many accessions displayed an immune response or a high level of resistance under field conditions, likely as a result of synergy between APR genes or between APR and seedling resistance genes. However, accessions with three or more seedling resistance genes had an overall lower field severity than those with two or fewer. Immune or highly resistant accessions are potential sources for improvement of leaf rust resistance. In addition, some lines were postulated to have known but unidentified genes/alleles or novel genes, also constituting potentially important sources of novel resistance.

Genic DNA methylation changes during in vitro organogenesis: organ specificity and conservation between parental lines of epialleles

During differentiation, in vitro organogenesis calls for the adjustment of the gene expression program toward a new fate. The role of epigenetic mechanisms including DNA methylation is suggested but little is known about the loci affected by DNA methylation changes, particularly in agronomic plants for witch in vitro technologies are useful such as sugar beet. Here, three pairs of organogenic and non-organogenic in vitro cell lines originating from different sugar beet (Beta vulgaris altissima) cultivars were used to assess the dynamics of DNA methylation at the global or genic levels during shoot or root regeneration. The restriction landmark genome scanning for methylation approach was applied to provide a direct quantitative epigenetic assessment of several CG methylated genes without prior knowledge of gene sequence that is particularly adapted for studies on crop plants without a fully sequenced genome. The cloned sequences had putative roles in cell proliferation, differentiation or unknown functions and displayed organ-specific DNA polymorphism for methylation and changes in expression during in vitro organogenesis. Among them, a potential ubiquitin extension protein 6 (UBI6) was shown, in different cultivars, to exhibit repeatable variations of DNA methylation and gene expression during shoot regeneration. In addition, abnormal development and callogenesis were observed in a T-DNA insertion mutant (ubi6) for a homologous sequence in Arabidopsis. Our data showed that DNA methylation is changed in an organ-specific way for genes exhibiting variations of expression and playing potential role during organogenesis. These epialleles could be conserved between parental lines opening perspectives for molecular markers.

Sex-specific DNA methylation and gene expression in andromonoecious poplar

The andromonoecious poplar is an exceptional model system for studying sex-specific flower development in dioecious plants. There is increasing evidence that epigenetic regulation, particularly DNA methylation, is an important regulatory factor during flower development. Here, methylation-sensitive amplified polymorphism (MSAP) was used to screen for sex-specific DNA methylation alterations in the andromonoecious poplar. The sequences of 27 sex-specific amplified fragments were obtained from DNA prepared from sex-specific flower tissues. PtGT2, PtPAL3, and PtCER4, which are homologous to MF26, MF29, and MF35, respectively, were cloned as candidate genes. Expression analysis and DNA methylation pattern profiling of the three candidate genes revealed that gene expression upregulation was always associated with gene body methylation. The results suggested that DNA methylation sites have the potential to regulate the genes' transcript levels. These three genes were shown to play important roles during different phases of flower development. This study will help to provide candidates for future experiments aimed at understanding the mechanism, whereby DNA methylation regulates gene expression in poplar.

KEY MESSAGES

We report the first screen for sex-specific DNA methylation alterations in the andromonoecious poplar. 27 sex-specific methylation sites were identified. The gene expression levels and DNA methylation patterns were detected for three candidate genes.