A major challenge for plants in a rapidly changing climate is to adapt to rising temperatures. Some plants adapt to temperature conditions by generating an epigenetic memory that can be transmitted both meiotically and mitotically. Such epigenetic memories may increase phenotypic variation to global warming and provide time for adaptation to occur through classical genetic selection. The goal of this study was to understand how warmer temperature conditions experienced during sexual and asexual reproduction affect the transcriptomes of different strawberry (Fragaria vesca) ecotypes. We let four European F. vesca ecotypes reproduce at two contrasting temperatures (18 and 28°C), either asexually through stolon formation for several generations, or sexually by seeds (achenes). We then analyzed the transcriptome of unfolding leaves, with emphasis on differential expression of genes belonging to the epigenetic machinery. For asexually reproduced plants we found a general transcriptomic response to temperature conditions but for sexually reproduced plants we found less significant responses. We predicted several splicing isoforms for important genes (e.g. a SOC1, LHY, and SVP homolog), and found significantly more differentially presented splicing event variants following asexual vs. sexual reproduction. This difference could be due to the stochastic character of recombination during meiosis or to differential creation or erasure of epigenetic marks during embryogenesis and seed development. Strikingly, very few differentially expressed genes were shared between ecotypes, perhaps because ecotypes differ greatly both genetically and epigenetically. Genes related to the epigenetic machinery were predominantly upregulated at 28°C during asexual reproduction but downregulated after sexual reproduction, indicating that temperature-induced change affects the epigenetic machinery differently during the two types of reproduction.

Plants must adapt with increasing speed to global warming to maintain their fitness. One rapid adaptation mechanism is epigenetic memory, which may provide organisms sufficient time to adapt to climate change. We studied how the perennial Fragaria vesca adapted to warmer temperatures (28°C vs. 18°C) over three asexual generations. Differences in flowering time, stolon number, and petiole length were induced by warmer temperature in one or more ecotypes after three asexual generations and persisted in a common garden environment. Induced methylome changes differed between the four ecotypes from Norway, Iceland, Italy, and Spain, but shared methylome responses were also identified. Most differentially methylated regions (DMRs) occurred in the CHG context, and most CHG and CHH DMRs were hypermethylated at the warmer temperature. In eight CHG DMR peaks, a highly similar methylation pattern could be observed between ecotypes. On average, 13% of the differentially methylated genes between ecotypes also showed a temperature-induced change in gene expression. We observed ecotype-specific methylation and expression patterns for genes related to gibberellin metabolism, flowering time, and epigenetic mechanisms. Furthermore, we observed a negative correlation with gene expression when repetitive elements were found near (±2 kb) or inside genes. In conclusion, lasting phenotypic changes indicative of an epigenetic memory were induced by warmer temperature and were accompanied by changes in DNA methylation patterns. Both shared methylation patterns and transcriptome differences between F. vesca accessions were observed, indicating that DNA methylation may be involved in both general and ecotype-specific phenotypic variation.

Temperature conditions experienced during embryogenesis and seed development may induce epigenetic changes that increase phenotypic variation in plants. Here we investigate if embryogenesis and seed development at two different temperatures (28 vs. 18°C) result in lasting phenotypic effects and DNA methylation changes in woodland strawberry (Fragaria vesca). Using five European ecotypes from Spain (ES12), Iceland (ICE2), Italy (IT4), and Norway (NOR2 and NOR29), we found statistically significant differences between plants from seeds produced at 18 or 28°C in three of four phenotypic features investigated under common garden conditions. This indicates the establishment of a temperature‐induced epigenetic memory‐like response during embryogenesis and seed development. The memory effect was significant in two ecotypes: in NOR2 flowering time, number of growth points and petiole length were affected, and in ES12 number of growth points was affected. This indicates that genetic differences between ecotypes in their epigenetic machinery, or other allelic differences, impact this type of plasticity. We observed statistically significant differences between ecotypes in DNA methylation marks in repetitive elements, pseudogenes, and genic elements. Leaf transcriptomes were also affected by embryonic temperature in an ecotype‐specific manner. Although we observed significant and lasting phenotypic change in at least some ecotypes, there was considerable variation in DNA methylation between individual plants within each temperature treatment. This within‐treatment variability in DNA methylation marks in F. vesca progeny may partly be a result of allelic redistribution from recombination during meiosis and subsequent epigenetic reprogramming during embryogenesis.

The influence of nitrogen on wood formation is well established. To gain insight into the underlying molecular mechanism, we first identified genes in 14 gene families that are involved in nitrogen uptake and metabolism in European aspen (Populus tremula L.) genome annotation. Gene expression data from a de novo RNA sequencing (RNA-seq) analysis and data available from the AspWood database (plantgenie.org) provided putative candidate genes for the uptake of nitrate, ammonium and amino acids from the xylem sap as well as their further assimilation in the secondary xylem tissues of the stem. For a population-wide analysis of the nitrogen-related genes, we utilized RNA-seq data from the cambial region of the stems of 5-year-old aspen trees, representing 99 natural aspen accessions, and compared the expression of the nitrogen-related genes to stem diameter. Novel regulatory interactions were identified in expression quantitative loci and co-expression network analyses in these data. The expression of certain nitrate and amino acid transporters correlated negatively with stem diameter, suggesting that excessive nitrogen retrieval from the xylem sap suppresses radial growth of the stem. The expression of a glutamine synthetase correlated with the expression of these transporters, a link further supported by increased plant growth in transgenic glutamine synthetase overexpressing trees. This study provides insight into the genetic basis of nitrogen uptake and assimilation and its connection to wood formation, providing interesting targets for improving nitrogen-use efficiency and growth of aspen trees.

Plants must quickly adapt to a changing environment in order to maintain their fitness. One rapid adaptation mechanism that promotes plasticity is epigenetic memory, which may provide long-lived organisms the precious time needed to adapt to climate change. In this study, we used the perennial plant Fragaria vesca as a model to determine how the methylome and transcriptome adapt to elevated temperatures (28 vs. 18 °C) over three asexual generations. Changes in flowering time, stolon number, and petiole length were induced in responses to temperature treatment in one or more ecotypes after three asexual generations in a manner indicative of an epigenetic memory. Induced methylome changes differed between four different ecotypes from Norway, Iceland, Italy, and Spain, but there were also some shared responses. Elevated temperature conditions induced significant phenotypic and methylation changes, particularly in the Norwegian ecotype. Most of the differentially methylated regions (DMRs) were in the CHG context, and most CHG and CHH DMRs were hypermethylated. Notably, the four ecotypes shared only eight CHG DMR peaks. Several differentially methylated genes (DMGs) also showed a change in gene expression. Ecotype-specific methylation and expression patterns were observed for genes related to gibberellin metabolism, flowering time, epigenetics. Furthermore, when repetitive elements (REs) were found near (±2 kb) or inside a gene, they showed a negative correlation with gene expression. In conclusion, phenotypic changes induced by elevated temperatures during asexual reproduction were accompanied by changes in DNA methylation patterns. Also, positional influences of REs impacted gene expression, indicating that DNA methylation may be involved in both general and ecotype-specific phenotypic plasticity in F. vesca .

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are key long-chain omega-3 fatty acids in fish nutrition, but their differential effects on Atlantic salmon under unpredictable chronic stress (UCS) remain unclear. This study compared hepatic responses to DHA- and EPA-rich diets under unstressed and UCS conditions. Atlantic salmon post-smolts were fed a low-EPA+DHA, DHA-rich, or EPA-rich diet for 10 weeks, followed by 3 weeks of UCS. Liver transcriptomes were analyzed by RNA sequencing, and selected genes were validated by quantitative reverse transcription PCR. Growth did not differ among dietary groups. Under unstressed conditions, the DHA-rich diet induced more differentially expressed genes than the EPA-rich diet (67 vs. 29) and affected pathways related to fatty acid metabolism, autophagy, cholesterol homeostasis, and antioxidant defense. After UCS, the EPA-rich diet induced a broader hepatic transcriptional response than the DHA-rich diet (205 vs. 57 differentially expressed genes), with only 12 genes shared between the two comparisons. Both diets affected fatty acid- and steroid-biosynthesis-related pathways, while gene-level responses were diet-specific. These findings reveal distinct, stress-dependent hepatic responses to dietary DHA and EPA and may inform future optimization of their nutritional provision in Atlantic salmon production.