Plant epigenetics: phenotypic and functional diversity beyond the DNA sequence

Epigenetics Regulation in Responses to Abiotic Factors in Plant Species: A Systematic Review

Plants have several mechanisms to adapt or acclimate to environmental stress. Morphological, physiological, or genetic changes are examples of complex plant responses. In recent years, our understanding of the role of epigenetic regulation, which encompasses changes that do not alter the DNA sequence, as an adaptive mechanism in response to stressful conditions has advanced significantly. Some studies elucidated and synthesized epigenetic mechanisms and their relationships with environmental change, while others explored the interplay between epigenetic modifications and environmental shifts, aiming to deepen our understanding of these complex processes. In this study, we performed a systematic review of the literature to analyze the progression of epigenetics studies on plant species' responses to abiotic factors. We also aimed to identify the most studied species, the type of abiotic factor studied, and the epigenetic technique most used in the scientific literature. For this, a search for articles in databases was carried out, and after analyzing them using pre-established inclusion criteria, a total of 401 studies were found. The most studied species were Arabidopsis thaliana and Oryza sativa, highlighting the gap in studies of non-economic and tropical plant species. Methylome DNA sequencing is the main technique used for the detection of epigenetic interactions in published studies. Furthermore, most studies sought to understand the plant responses to abiotic changes in temperature, water, and salinity. It is worth emphasizing further research is necessary to establish a correlation between epigenetic responses and abiotic factors, such as extreme temperatures and light, associated with climate change.

Chloroplast DNA methylation in the kelp Saccharina latissima is determined by origin and possibly influenced by cultivation

DNA cytosine methylation is an important epigenetic mechanism in genomic DNA. In most land plants, it is absent in the chloroplast DNA. We detected methylation in the chloroplast DNA of the kelp Saccharina latissima, a non-model macroalgal species of high ecological and economic importance. Since the functional role of the chloroplast methylome is yet largely unknown, this fundamental research assessed the chloroplast DNA cytosine methylation in wild and laboratory raised kelp from different climatic origins (High-Arctic at 79° N, and temperate at 54° N), and in laboratory samples from these origins raised at different temperatures (5, 10 and 15°C). Results suggest genome-wide differences in methylated sites and methylation level between the origins, while rearing temperature had only weak effects on the chloroplast methylome. Our findings point at the importance of matching conditions to origin in restoration and cultivation processes to be valid even on plastid level.

Grafting based DNA methylation alteration of snoRNAs in upland cotton (Gossypium L.)

The effects of grafting in response to various biotic and abiotic stressors have been studied, however, the methylation status of small nucleolar RNA (snoRNA) genes in heterograft and homograft cotton needs investigation. This study was undertaken to determine grafting effects on DNA methylation of snoRNA genes in Upland cotton. Rootstocks used were Pima 3-79 (Gossypium barbadense acc. Pima 3-79) and Texas Marker-1 (G. hirsutum acc. TM-1), representing two different species with different fiber properties, adaptations, and morphologies. The methylation ratio and differently methylated cytosines (DMCs) of 10935 snoRNA genes in mature seeds of heterograft and homograft cotton samples were studied using the whole genome bisulfite sequencing method. Seedling vigor and seed weight were studied to investigate phenotype alterations that might be associated with altered methylation levels among grafts. Statistically significant DMC differences among gene elements of snoRNA genes and between homograft and heterograft cotton samples were identified in the absence of DNA sequence alterations. DNA methylation alterations of snoRNA genes associated with seedling vigor and 100 seed weight. The majority of snoRNA genes showed higher numbers of mCG + mCHG-DMCs with increased methylation levels in heterograft, while there were higher numbers of mCG + mCHG-DMCs with decreased methylation levels in homograft. Since snoRNAs regulate essential genes for plant growth and development and plant adaptation to different habitats or extreme environments, their altered methylation levels should be related with plant physiology.

High-quality haplotype-resolved genome assembly for ring-cup oak (Quercus glauca) provides insight into oaks demographic dynamics

Quercus section Cyclobalanopsis represents a dominant woody lineage in East Asian evergreen broadleaved forests. Regardless of its ecological and economic importance, little is known about the genomes of species in this unique oak lineage. Quercus glauca is one of the most widespread tree species in the section Cyclobalanopsis. In this study, a high-quality haplotype-resolved reference genome was assembled for Q. glauca from PacBio HiFi and Hi-C reads. The genome size, contig N50, and scaffold N50 measured 902.88, 7.60, and 69.28 Mb, respectively, for haplotype1, and 913.28, 7.20, and 71.53 Mb, respectively, for haplotype2. A total of 37,457 and 38,311 protein-coding genes were predicted in haplotype1 and haplotype2, respectively. Homologous chromosomes in the Q. glauca genome had excellent gene pair collinearity. The number of R-genes in Q. glauca was similar to most East Asian oaks but less than oak species from Europe and America. Abundant structural variation in the Q. glauca genome could contribute to environmental stress tolerance in Q. glauca. Sections Cyclobalanopsis and Cerris diverged in the Oligocene, in agreement with fossil records for section Cyclobalanopsis, which document its presence in East Asia since the early Miocene. The demographic dynamics of closely related oak species were largely similar. The high-quality reference genome provided here for the most widespread species in section Cyclobalanopsis will serve as an essential genomic resource for evolutionary studies of key oak lineages while also supporting studies of interspecific introgression, local adaptation, and speciation in oaks.

The sugar kelp Saccharina latissima I: recent advances in a changing climate

BACKGROUND

The sugar kelp Saccharina latissima is a Laminariales species widely distributed in the Northern Hemisphere. Its physiology and ecology have been studied since the 1960s, given its ecological relevance on western temperate coasts. However, research interest has been rising recently, driven mainly by reports of negative impacts of anthropogenically induced environmental change and by the increased commercial interest in cultivating the species, with several industrial applications for the resulting biomass.

SCOPE

We used a variety of sources published between 2009 to May 2023 (but including some earlier literature where required), to provide a comprehensive review of the ecology, physiology, biochemical and molecular biology of S. latissima. In so doing we aimed to better understand the species' response to stressors in natural communities, but also inform the sustainable cultivation of the species.

CONCLUSION

Due to its wide distribution, S. latissima has developed a variety of physiological and biochemical mechanisms to adjust to environmental changes, including adjustments in photosynthetic parameters, modulation of osmolytes and antioxidants, reprogramming of gene expression and epigenetic modifications, among others summarized in this review. This is particularly important because massive changes in the abundance and distribution of S. latissima have already been observed. Namely, presence and abundance of S. latissima has significantly decreased at the rear edges on both sides of the Atlantic, and increased in abundance at the polar regions. These changes were mainly caused by climate change and will therefore be increasingly evident in the future. Recent developments in genomics, transcriptomics and epigenomics have clarified the existence of genetic differentiation along its distributional range with implications in the fitness at some locations. The complex biotic and abiotic interactions unraveled here demonstrated the cascading effects the disappearance of a kelp forest can have in a marine ecosystem. We show how S. latissima is an excellent model to study acclimation and adaptation to environmental variability and how to predict future distribution and persistence under climate change.

EasyDAM_V4: Guided-GAN-based cross-species data labeling for fruit detection with significant shape difference

Traditional agriculture is gradually being combined with artificial intelligence technology. High-performance fruit detection technology is an important basic technology in the practical application of modern smart orchards and has great application value. At this stage, fruit detection models need to rely on a large number of labeled datasets to support the training and learning of detection models, resulting in higher manual labeling costs. Our previous work uses a generative adversarial network to translate the source domain to the target fruit images. Thus, automatic labeling is performed on the actual dataset in the target domain. However, the method still does not achieve satisfactory results for translating fruits with significant shape variance. Therefore, this study proposes an improved fruit automatic labeling method, EasyDAM_V4, which introduces the Across-CycleGAN fruit translation model to achieve spanning translation between phenotypic features such as fruit shape, texture, and color to reduce domain differences effectively. We validated the proposed method using pear fruit as the source domain and three fruits with large phenotypic differences, namely pitaya, eggplant, and cucumber, as the target domain. The results show that the EasyDAM_V4 method achieves substantial cross-fruit shape translation, and the average accuracy of labeling reached 87.8, 87.0, and 80.7% for the three types of target domain datasets, respectively. Therefore, this research method can improve the applicability of the automatic labeling process even if significant shape variance exists between the source and target domain.

Phenotypic and genetic characterization of an Avena sativa L. germplasm collection of diverse origin: implications for food-oat breeding in Chile

Oats are known for their nutritional value and also for their beneficial properties on human health, such as the reduction of cholesterol levels and risk of coronary heart disease; they are an important export product for Chile. During the last decade (2010-2022) over 90% of the oat cultivated area in Chile has been covered with Avena sativa L. cv. Supernova INIA. This lack of genetic diversity in a context of climate change could limit the long-term possibility of growing oats in Chile. The present study is a phenotypic and genetic analysis of 132 oat cultivars and pure lines of diverse origin that can be considered as potential breeding material. The germplasm was evaluated for 28 traits and analyzed with 14 SSR markers. The effects of genotypes on phenotype were significant over all traits (P ≤ 0.05). Most traits exhibited moderate to high broad-sense heritability with exceptions such as yield (H2 = 0.27) and hulls staining (H2 = 0.32). Significant undesirable correlations between traits were generally of small biological importance, which is auspicious for achieving breeding objectives. Some of the heritability data and correlations provided here have not been previously reported. The overall phenotypic diversity was high (H' = 0.68 ± 0.18). The germplasm was grouped into three phenotypic clusters, differing in their qualities for breeding. Twenty-six genotypes outperforming Supernova INIA were identified for breeding of conventional food-oats. The genetic diversity of the germplasm was moderate on average (He = 0.58 ± 0.03), varying between 0.32 (AM22) and 0.77 (AME178). Two genetic subpopulations supported by the Structure algorithm exhibited a genetic distance of 0.24, showing low divergence of the germplasm. The diversity and phenotypic values found in this collection of oat genotypes are promising with respect to obtaining genetic gain in the short term in breeding programs. However, the similar genetic diversity, higher phenotypic diversity, and better phenotypic performance of the germplasm created in Chile compared to foreign germplasm suggest that germplasm harboring new genetic diversity will be key to favor yield and quality in new oat cultivars in the long term.

Epigenetic weapons in plant-herbivore interactions: Sulforaphane disrupts histone deacetylases, gene expression, and larval development in Spodoptera exigua while the specialist feeder Trichoplusia ni is largely resistant to these effects

Cruciferous plants produce sulforaphane (SFN), an inhibitor of nuclear histone deacetylases (HDACs). In humans and other mammals, the consumption of SFN alters enzyme activities, DNA-histone binding, and gene expression within minutes. However, the ability of SFN to act as an HDAC inhibitor in nature, disrupting the epigenetic machinery of insects feeding on these plants, has not been explored. Here, we demonstrate that SFN consumed in the diet inhibits the activity of HDAC enzymes and slows the development of the generalist grazer Spodoptera exigua, in a dose-dependent fashion. After consuming SFN for seven days, the activities of HDAC enzymes in S. exigua were reduced by 50%. Similarly, larval mass was reduced by 50% and pupation was delayed by 2-5 days, with no additional mortality. Similar results were obtained when SFN was applied topically to eggs. RNA-seq analyses confirm that SFN altered the expression of thousands of genes in S. exigua. Genes associated with energy conversion pathways were significantly downregulated while those encoding for ribosomal proteins were dramatically upregulated in response to the consumption of SFN. In contrast, the co-evolved specialist feeder Trichoplusia ni was not negatively impacted by SFN, whether it was consumed in their diet at natural concentrations or applied topically to eggs. The activities of HDAC enzymes were not inhibited and development was not disrupted. In fact, SFN exposure sometimes accelerated T. ni development. RNA-seq analyses revealed that the consumption of SFN alters gene expression in T. ni in similar ways, but to a lesser degree, compared to S. exigua. This apparent resistance of T. ni can be overwhelmed by unnaturally high levels of SFN or by exposure to more powerful pharmaceutical HDAC inhibitors. These results demonstrate that dietary SFN interferes with the epigenetic machinery of insects, supporting the hypothesis that plant-derived HDAC inhibitors serve as "epigenetic weapons" against herbivores.

Herbivory induced methylation changes in the Lombardy poplar: A comparison of results obtained by epiGBS and WGBS

DNA cytosine methylation is an epigenetic mechanism involved in regulation of plant responses to biotic and abiotic stress and its ability to change can vary with the sequence context in which a cytosine appears (CpG, CHG, CHH, where H = Adenine, Thymine, Cytosine). Quantification of DNA methylation in model plant species is frequently addressed by Whole Genome Bisulfite Sequencing (WGBS), which requires a good-quality reference genome. Reduced Representation Bisulfite Sequencing (RRBS) is a cost-effective potential alternative for ecological research with limited genomic resources and large experimental designs. In this study, we provide for the first time a comprehensive comparison between the outputs of RRBS and WGBS to characterize DNA methylation changes in response to a given environmental factor. In particular, we used epiGBS (recently optimized RRBS) and WGBS to assess global and sequence-specific differential methylation after insect and artificial herbivory in clones of Populus nigra cv. 'italica'. We found that, after any of the two herbivory treatments, global methylation percentage increased in CHH, and the shift was detected as statistically significant only by epiGBS. As regards to loci-specific differential methylation induced by herbivory (cytosines in epiGBS and regions in WGBS), both techniques indicated the specificity of the response elicited by insect and artificial herbivory, together with higher frequency of hypo-methylation in CpG and hyper-methylation in CHH. Methylation changes were mainly found in gene bodies and intergenic regions when present at CpG and CHG and in transposable elements and intergenic regions at CHH context. Thus, epiGBS succeeded to characterize global, genome-wide methylation changes in response to herbivory in the Lombardy poplar. Our results support that epiGBS could be particularly useful in large experimental designs aimed to explore epigenetic changes of non-model plant species in response to multiple environmental factors.

Exploring the crop epigenome: a comparison of DNA methylation profiling techniques

Epigenetic modifications play a vital role in the preservation of genome integrity and in the regulation of gene expression. DNA methylation, one of the key mechanisms of epigenetic control, impacts growth, development, stress response and adaptability of all organisms, including plants. The detection of DNA methylation marks is crucial for understanding the mechanisms underlying these processes and for developing strategies to improve productivity and stress resistance of crop plants. There are different methods for detecting plant DNA methylation, such as bisulfite sequencing, methylation-sensitive amplified polymorphism, genome-wide DNA methylation analysis, methylated DNA immunoprecipitation sequencing, reduced representation bisulfite sequencing, MS and immuno-based techniques. These profiling approaches vary in many aspects, including DNA input, resolution, genomic region coverage, and bioinformatics analysis. Selecting an appropriate methylation screening approach requires an understanding of all these techniques. This review provides an overview of DNA methylation profiling methods in crop plants, along with comparisons of the efficacy of these techniques between model and crop plants. The strengths and limitations of each methodological approach are outlined, and the importance of considering both technical and biological factors are highlighted. Additionally, methods for modulating DNA methylation in model and crop species are presented. Overall, this review will assist scientists in making informed decisions when selecting an appropriate DNA methylation profiling method.

Differences by origin in methylome suggest eco-phenotypes in the kelp Saccharina latissima

Most kelp species are of high ecological and economic importance worldwide, but are highly susceptible to rising ocean temperatures due to their sessile lifestyle. Due to interference with reproduction, development and growth, natural kelp forests have vanished in multiple regions after extreme summer heat waves. Furthermore, increasing temperatures are likely to decrease biomass production and, thus, reduce production security of farmed kelp. Epigenetic variation, and cytosine methylation as a heritable epigenetic trait, is a rapid means of acclimation and adaptation to environmental conditions, including temperature. While the first methylome of brown macroalgae has been recently described in the kelp Saccharina japonica, its functional relevance and contribution to environmental acclimation is currently unknown. The main objective of our study was to identify the importance of the methylome in the congener kelp species Saccharina latissima for temperature acclimation. Our study is the first to compare DNA methylation in kelp between wild populations of different latitudinal origin, and the first to investigate the effect of cultivation and rearing temperature on genome-wide cytosine methylation. Origin appears to determine many traits in kelp, but it is unknown to what extent the effects of thermal acclimation may be overruled by lab-related acclimation. Our results suggest that seaweed hatchery conditions have strong effects on the methylome and, thus, putatively on the epigenetically controlled characteristics of young kelp sporophytes. However, culture origin could best explain epigenetic differences in our samples suggesting that epigenetic mechanisms contribute to local adaptation of eco-phenotypes. Our study is a first step to understand whether DNA methylation marks (via their effect on gene regulation) may be used as biological regulators to enhance production security and kelp restoration success under rising temperatures, and highlights the importance to match hatchery conditions to origin.

Epigenetic variation: A major player in facilitating plant fitness under changing environmental conditions

Recent research in plant epigenetics has increased our understanding of how epigenetic variability can contribute to adaptive phenotypic plasticity in natural populations. Studies show that environmental changes induce epigenetic switches either independently or in complementation with the genetic variation. Although most of the induced epigenetic variability gets reset between generations and is short-lived, some variation becomes transgenerational and results in heritable phenotypic traits. The short-term epigenetic responses provide the first tier of transient plasticity required for local adaptations while transgenerational epigenetic changes contribute to stress memory and help the plants respond better to recurring or long-term stresses. These transgenerational epigenetic variations translate into an additional tier of diversity which results in stable epialleles. In recent years, studies have been conducted on epigenetic variation in natural populations related to various biological processes, ecological factors, communities, and habitats. With the advent of advanced NGS-based technologies, epigenetic studies targeting plants in diverse environments have increased manifold to enhance our understanding of epigenetic responses to environmental stimuli in facilitating plant fitness. Taking all points together in a frame, the present review is a compilation of present-day knowledge and understanding of the role of epigenetics and its fitness benefits in diverse ecological systems in natural populations.

Machine learning: its challenges and opportunities in plant system biology

Sequencing technologies are evolving at a rapid pace, enabling the generation of massive amounts of data in multiple dimensions (e.g., genomics, epigenomics, transcriptomic, metabolomics, proteomics, and single-cell omics) in plants. To provide comprehensive insights into the complexity of plant biological systems, it is important to integrate different omics datasets. Although recent advances in computational analytical pipelines have enabled efficient and high-quality exploration and exploitation of single omics data, the integration of multidimensional, heterogenous, and large datasets (i.e., multi-omics) remains a challenge. In this regard, machine learning (ML) offers promising approaches to integrate large datasets and to recognize fine-grained patterns and relationships. Nevertheless, they require rigorous optimizations to process multi-omics-derived datasets. In this review, we discuss the main concepts of machine learning as well as the key challenges and solutions related to the big data derived from plant system biology. We also provide in-depth insight into the principles of data integration using ML, as well as challenges and opportunities in different contexts including multi-omics, single-cell omics, protein function, and protein-protein interaction. KEY POINTS: • The key challenges and solutions related to the big data derived from plant system biology have been highlighted. • Different methods of data integration have been discussed. • Challenges and opportunities of the application of machine learning in plant system biology have been highlighted and discussed.

Genetic and Epigenetic Differentiation Across Intertidal Gradients in the Foundation Plant Spartina alterniflora

Ecological genomics approaches have informed us about the structure of genetic diversity in natural populations that might underlie patterns in trait variation. However, we still know surprisingly little about the mechanisms that permit organisms to adapt to variable environmental conditions. The salt marsh foundation plant Spartina alterniflora exhibits a dramatic range in phenotype that is associated with a pronounced intertidal environmental gradient across a narrow spatial scale. Both genetic and non-genetic molecular mechanisms might underlie this phenotypic variation. To investigate both, we used epigenotyping-by-sequencing (epiGBS) to evaluate the make-up of natural populations across the intertidal environmental gradient. Based on recent findings, we expected that both DNA sequence and DNA methylation diversity would be explained by source population and habitat within populations. However, we predicted that epigenetic variation might be more strongly associated with habitat since similar epigenetic modifications could be rapidly elicited across different genetic backgrounds by similar environmental conditions. Overall, with PERMANOVA we found that population of origin explained a significant amount of the genetic (8.6%) and epigenetic (3.2%) variance. In addition, we found that a small but significant amount of genetic and epigenetic variance (<1%) was explained by habitat within populations. The interaction of population and habitat explained an additional 2.9% of the genetic variance and 1.4% of the epigenetic variance. By examining genetic and epigenetic variation within the same fragments (variation in close-cis), we found that population explained epigenetic variation in 9.2% of 8,960 tested loci, even after accounting for differences in the DNA sequence of the fragment. Habitat alone explained very little (<0.1%) of the variation in these close-cis comparisons, but the interaction of population and habitat explained 2.1% of the epigenetic variation in these loci. Using multiple matrix regression with randomization (MMRR) we found that phenotypic differences in natural populations were correlated with epigenetic and environmental differences even when accounting for genetic differences. Our results support the contention that sequence variation explains most of the variation in DNA methylation, but we have provided evidence that DNA methylation distinctly contributes to plant responses in natural populations.

Genetic and Epigenetic Signatures Associated with the Divergence of Aquilegia Species

Widely grown in the Northern Hemisphere, the genus Aquilegia (columbine) is a model system in adaptive radiation research. While morphological variations between species have been associated with environmental factors, such as pollinators, how genetic and epigenetic factors are involved in the rapid divergence in this genus remains under investigated. In this study, we surveyed the genomes and DNA methylomes of ten Aquilegia species, representative of the Asian, European and North American lineages. Our analyses of the phylogeny and population structure revealed high genetic and DNA methylomic divergence across these three lineages. By multi-level genome-wide scanning, we identified candidate genes exhibiting lineage-specific genetic or epigenetic variation patterns that were signatures of inter-specific divergence. We demonstrated that these species-specific genetic variations and epigenetic variabilities are partially independent and are both functionally related to various biological processes vital to adaptation, including stress tolerance, cell reproduction and DNA repair. Our study provides an exploratory overview of how genetic and epigenetic signatures are associated with the diversification of the Aquilegia species.

Gene-body methylation in plants: mechanisms, functions and important implications for understanding evolutionary processes

Gene body methylation (gbM) is an epigenetic mark where gene exons are methylated in the CG context only, as opposed to CHG and CHH contexts (where H stands for A, C, or T). CG methylation is transmitted transgenerationally in plants, opening the possibility that gbM may be shaped by adaptation. This presupposes, however, that gbM has a function that affects phenotype, which has been a topic of debate in the literature. Here, we review our current knowledge of gbM in plants. We start by presenting the well-elucidated mechanisms of plant gbM establishment and maintenance. We then review more controversial topics: the evolution of gbM and the potential selective pressures that act on it. Finally, we discuss the potential functions of gbM that may affect organismal phenotypes: gene expression stabilization and upregulation, inhibition of aberrant transcription (reverse and internal), prevention of aberrant intron retention, and protection against TE insertions. To bolster the review of these topics, we include novel analyses to assess the effect of gbM on transcripts. Overall, a growing body of literature finds that gbM correlates with levels and patterns of gene expression. It is not clear, however, if this is a causal relationship. Altogether, functional work suggests that the effects of gbM, if any, must be relatively small, but there is nonetheless evidence that it is shaped by natural selection. We conclude by discussing the potential adaptive character of gbM and its implications for an updated view of the mechanisms of adaptation in plants.

Epigenetic regulation of thermomorphogenesis in Arabidopsis thaliana

Temperature is a key factor in determining plant growth and development, geographical distribution, and seasonal behavior. Plants accurately sense subtle changes in ambient temperature and alter their growth and development accordingly to improve their chances of survival and successful propagation. Thermomorphogenesis encompasses a variety of morphological changes that help plants acclimate to warm environmental temperatures. Revealing the molecular mechanism of thermomorphogenesis is important for breeding thermo-tolerant crops and ensuring food security under global climate change. Plant adaptation to elevated ambient temperature is regulated by multiple signaling pathways and epigenetic mechanisms such as histone modifications, histone variants, and non-coding RNAs. In this review, we summarize recent advances in the mechanism of epigenetic regulation during thermomorphogenesis with a focus on the model plant Arabidopsis thaliana and briefly discuss future prospects for this field.

Can Forest Trees Cope with Climate Change?-Effects of DNA Methylation on Gene Expression and Adaptation to Environmental Change

Epigenetic modifications, including chromatin modifications and DNA methylation, play key roles in regulating gene expression in both plants and animals. Transmission of epigenetic markers is important for some genes to maintain specific expression patterns and preserve the status quo of the cell. This article provides a review of existing research and the current state of knowledge about DNA methylation in trees in the context of global climate change, along with references to the potential of epigenome editing tools and the possibility of their use for forest tree research. Epigenetic modifications, including DNA methylation, are involved in evolutionary processes, developmental processes, and environmental interactions. Thus, the implications of epigenetics are important for adaptation and phenotypic plasticity because they provide the potential for tree conservation in forest ecosystems exposed to adverse conditions resulting from global warming and regional climate fluctuations.

Protein Crotonylation Expert Review: A New Lens to Take Post-Translational Modifications and Cell Biology to New Heights

Genome regulation, temporal and spatial variations in cell function, continues to puzzle and interest life scientists who aim to unravel the molecular basis of human health and disease, not to mention plant biology and ecosystem diversity. Despite important advances in epigenomics and protein post-translational modifications over the past decade, there is a need for new conceptual lenses to understand biological mechanisms that can help unravel the fundamental regulatory questions in genomes and the cell. To these ends, lys crotonylation (Kcr) is a reversible protein modification catalyzed by protein crotonyl transferases and decrotonylases. First identified on histones, Kcr regulates cellular processes at the chromatin level. Research thus far has revealed that Kcr marks promoter sites of active genes and potential enhancers. Eventually, Kcr on a number of nonhistone proteins was reported. The abundance of Kcr on ribosomal and myofilament proteins indicates its functional roles in protein synthesis and muscle contraction. Kcr has also been associated with pluripotency, spermiogenesis, and DNA repair. In plants, large-scale mass spectrometry-based experiments validated the roles of Kcr in photosynthesis. In this expert review, we present the latest thinking and findings on lys crotonylation with an eye to regulation of cell biology. We discuss the enrichment techniques, putative biological functions, and challenges associated with studying this protein modification with vast biological implications. Finally, we reflect on the future outlook about the broader relevance of Kcr in animals, microbes, and plant species.