Complex evolutionary history and diverse domain organization of SET proteins suggest divergent regulatory interactions

H3K36 methyltransferase GhKMT3;1a and GhKMT3;2a promote flowering in upland cotton

BACKGROUND

The SET domain group (SDG) genes encode histone lysine methyltransferases, which regulate gene transcription by altering chromatin structure and play pivotal roles in plant flowering determination. However, few studies have investigated their role in the regulation of flowering in upland cotton.

RESULTS

A total of 86 SDG genes were identified through genome-wide analysis in upland cotton (Gossypium hirsutum). These genes were unevenly distributed across 25 chromosomes. Cluster analysis revealed that the 86 GhSDGs were divided into seven main branches. RNA-seq data and qRT‒PCR analysis revealed that lysine methyltransferase 3 (KMT3) genes were expressed at high levels in stamens, pistils and other floral organs. Using virus-induced gene silencing (VIGS), functional characterization of GhKMT3;1a and GhKMT3;2a revealed that, compared with those of the controls, the GhKMT3;1a- and GhKMT3;2a-silenced plants exhibited later budding and flowering and lower plant heightwere shorter. In addition, the expression of flowering-related genes (GhAP1, GhSOC1 and GhFT) significantly decreased and the expression level of GhSVP significantly increased in the GhKMT3;1a- and GhKMT3;2a-silenced plants compared with the control plants.

CONCLUSION

A total of 86 SDG genes were identified in upland cotton, among which GhKMT3;1a and GhKMT3;2a might regulate flowering by affecting the expression of GhAP1, GhSOC1, GhFT and GhSVP. These findings will provide genetic resources for advanced molecular breeding in the future.

Molecular mechanisms and regulation of recombination frequency and distribution in plants

KEY MESSAGE

Recent developments in understanding the distribution and distinctive features of recombination hotspots are reviewed and approaches are proposed to increase recombination frequency in coldspot regions. Recombination events during meiosis provide the foundation and premise for creating new varieties of crops. The frequency of recombination in different genomic regions differs across eukaryote species, with recombination generally occurring more frequently at the ends of chromosomes. In most crop species, recombination is rare in centromeric regions. If a desired gene variant is linked in repulsion with an undesired variant of a second gene in a region with a low recombination rate, obtaining a recombinant plant combining two favorable alleles will be challenging. Traditional crop breeding involves combining desirable genes from parental plants into offspring. Therefore, understanding the mechanisms of recombination and factors affecting the occurrence of meiotic recombination is important for crop breeding. Here, we review chromosome recombination types, recombination mechanisms, genes and proteins involved in the meiotic recombination process, recombination hotspots and their regulation systems and discuss how to increase recombination frequency in recombination coldspot regions.

Case report: De novo variant of SETD1A causes infantile epileptic spasms syndrome

Infantile epileptic spasms syndrome (IESS) is one of the most common epileptic encephalopathies of infancy, with typical clinical features defined by a triad of epileptic spasms, hypsarrhythmia, and developmental delay. Genetic factors are important causes of IESS. The SETD1A (SET Domain Containing 1A) gene encodes a histone lysine methyltransferase that activates gene transcription through histone H3 lysine K4 methylation. Mutations in the SETD1A gene have been associated with schizophrenia, and some have been reported to cause seizures. Herein, we report a case of IESS caused by a SETD1A gene mutation. Video electroencephalography showed hypsarrhythmia. No specific findings were obtained after brain MRI and metabolic work-up. The seizures disappeared after treatment with adrenocorticotropic hormone, vitamin B6, and valproic acid during hospitalization. Genetic testing revealed that the child had a variant (NM_014712.3:c.3005_3,006 delAG, p.Glu1002Glyfs*20) in exon 12 of the SETD1A gene, representing a de novo mutation. There have been no previous reports on the SETD1A gene causing infantile spasms. We also summarize the existing literature on SETD1A gene-related epilepsy to provide a reference for clinical diagnosis and treatment.

Dynamics of epigenetic control in plants via SET domain containing proteins: Structural and functional insights

Plants control expression of their genes in a way that involves manipulating the chromatin structural dynamics in order to adapt to environmental changes and carry out developmental processes. Histone modifications like histone methylation are significant epigenetic marks which profoundly and globally modify chromatin, potentially affecting the expression of several genes. Methylation of histones is catalyzed by histone lysine methyltransferases (HKMTs), that features an evolutionary conserved domain known as SET [Su(var)3-9, E(Z), Trithorax]. This methylation is directed at particular lysine (K) residues on H3 or H4 histone. Plant SET domain group (SDG) proteins are categorized into different classes that have been conserved through evolution, and each class have specificity that influences how the chromatin structure operates. The domains discovered in plant SET domain proteins have typically been linked to protein-protein interactions, suggesting that majority of the SDGs function in complexes. Additionally, SDG-mediated histone mark deposition also affects alternative splicing events. In present review, we discussed the diversity of SDGs in plants including their structural properties. Additionally, we have provided comprehensive summary of the functions of the SDG-domain containing proteins in plant developmental processes and response to environmental stimuli have also been highlighted.

Neurobehavioral characteristics of mice with SETD5 mutations as models of IDD23 and KBG syndromes

Genomic analysis has revealed that the genes for various chromatin regulators are mutated in many individuals with neurodevelopmental disorders (NDDs), emphasizing the important role of chromatin regulation in nervous system development and function. Chromatin regulation is mediated by writers, readers, and erasers of histone and DNA modifications, with such proteins being defined by specific domains. One of these domains is the SET domain, which is present in enzymes that catalyze histone methylation. Heterozygous loss-of-function mutations of the SETD5 (SET domain containing 5) gene have been identified in individuals with an NDD designated IDD23 (intellectual developmental disorder, autosomal dominant 23). KBG syndrome (named after the initials of the last names of the first three families identified with the condition) is characterized by features that either overlap with or are distinct from those of IDD23 and was initially thought to be caused only by mutations in the ANKRD11 (ankyrin repeat domain containing 11) gene. However, recent studies have identified SETD5 mutations in some KBG syndrome patients without ANKRD11 mutations. Here we summarize the neurobehavioral characterization of Setd5 ^+/- mice performed by four independent research groups, compare IDD23 and KBG phenotypes, and address the utility and future development of mouse models for elucidation of the mechanisms underlying NDD pathogenesis, with a focus on SETD5 and its related proteins.

Large-scale analyses of angiosperm Flowering Locus T genes reveal duplication and functional divergence in monocots

FLOWERING LOCUS T (FT) are well-known key genes for initiating flowering in plants. Delineating the evolutionary history and functional diversity of FT genes is important for understanding the diversification of flowering time and how plants adapt to the changing surroundings. We performed a comprehensive phylogenetic analysis of FT genes in 47 sequenced flowering plants and the 1,000 Plant Transcriptomes (1KP) database with a focus on monocots, especially cereals. We revealed the evolutionary history of FT genes. The FT genes in monocots can be divided into three clades (I, II, and III), whereas only one monophyletic group was detected in early angiosperms, magnoliids, and eudicots. Multiple rounds of whole-genome duplications (WGD) events followed by gene retention contributed to the expansion and variation of FT genes in monocots. Amino acid sites in the clade II and III genes were preferentially under high positive selection, and some sites located in vital domain regions are known to change functions when mutated. Clade II and clade III genes exhibited high variability in important regions and functional divergence compared with clade I genes; thus, clade I is more conserved than clade II and III. Genes in clade I displayed higher expression levels in studied organs and tissues than the clade II and III genes. The co-expression modules showed that some of the FT genes might have experienced neofunctionalization and subfunctionalization, such as the acquisition of environmental resistance. Overall, FT genes in monocots might form three clades by the ancient gene duplication, and each clade was subsequently subjected to different selection pressures and amino acid substitutions, which eventually led to different expression patterns and functional diversification. Our study provides a global picture of FT genes' evolution in monocots, paving a road for investigating FT genes' function in future.

Identification of epigenetic histone modifications and analysis of histone lysine methyltransferases in Alexandrium pacificum

Alexandrium pacificum is a toxic dinoflagellate that can cause harmful algal blooms (HABs). The molecular mechanisms of HABs are still poorly understood, especially at the epigenetics level. Organism growth and metabolic processes are affected by histone modifications, an important mode of epigenetic regulation. In this study, various types of modifications, including methylation, acetylation, ubiquitination, and phosphorylation in A. pacificum cells were identified by using pan-antibodies, mass spectrometry, and an H3 modification multiplex assay kit. The modification abundance of H3K4me2 and H3K27me3 of A. pacificum varied under different growth conditions detected by Western blots. A class of SET domain genes (SDGs) encoding histone lysine methyltransferase was analyzed. A total of 179 SDG members were identified in A. pacificum, of which 53 sequences encoding complete proteins were classified into three categories by phylogenetic analysis, conserved domains and motifs analysis. Expression analysis and real-time polymerase chain reaction validation showed that the expressions of some SDGs were significantly influenced by light, nitrogen, phosphorus and manganese supplements. The results revealed that histone lysine methylation played an important role in responding to HABs inducing conditions. This study provided useful information for the further exploration of the role and regulatory mechanism of SDGs in the rapid growth of A. pacificum.

Transcription-coupled and epigenome-encoded mechanisms direct H3K4 methylation

Mono-, di-, and trimethylation of histone H3 lysine 4 (H3K4me1/2/3) are associated with transcription, yet it remains controversial whether H3K4me1/2/3 promote or result from transcription. Our previous characterizations of Arabidopsis H3K4 demethylases suggest roles for H3K4me1 in transcription. However, the control of H3K4me1 remains unexplored in Arabidopsis, in which no methyltransferase for H3K4me1 has been identified. Here, we identify three Arabidopsis methyltransferases that direct H3K4me1. Analyses of their genome-wide localization using ChIP-seq and machine learning reveal that one of the enzymes cooperates with the transcription machinery, while the other two are associated with specific histone modifications and DNA sequences. Importantly, these two types of localization patterns are also found for the other H3K4 methyltransferases in Arabidopsis and mice. These results suggest that H3K4me1/2/3 are established and maintained via interplay with transcription as well as inputs from other chromatin features, presumably enabling elaborate gene control.

Genome-wide identification, classification and expression analysis of the JmjC domain-containing histone demethylase gene family in Jatropha curcas L

JmjC domain-containing proteins, an important family of histone lysine demethylase, play significant roles in maintaining the homeostasis of histone methylation. In this study, we comprehensively analyzed the JmjC domain-containing gene family in Jatropha curcas and found 20 JmjC domain-containing genes (JcJMJ genes). Phylogenetic analysis revealed that these JcJMJ genes can be classified into five major subgroups, and genes in each subgroup had similar motif and domain composition. Cis-regulatory element analysis showed that the number and types of cis-regulatory elements owned by the promoter of JcJMJ genes in different subgroup were significantly different. Moreover, miRNA target prediction result revealed a complicated miRNA-mediated post-transcriptional regulatory network, in which JcJMJ genes were regulated by different numbers and types of miRNAs. Further analysis of the tissue and stress expression profiles showed that many JcJMJ genes had tissue and stress expression specificity. All these results provided valuable information for understanding the evolution of JcJMJ genes and the complex transcriptional and post transcriptional regulation involved, and laid the foundation for further functional analysis of JcJMJ genes.

Phylogenetic profiling resolves early emergence of PRC2 and illuminates its functional core

This study strengthens the support for PRC2 emergence before the diversification of eukaryotes, detects a common presence of E(z) and ESC, indicating a conserved core, identifies diverse VEFS-Box Su(z)12 candidate proteins, and proposes a substrate specificity shift during E(z) evolution.

Polycomb repressive complex 2 (PRC2) is involved in maintaining transcriptionally silent chromatin states through methylating lysine 27 of histone H3 by the catalytic subunit enhancer of zeste [E(z)]. Here, we report the diversity of PRC2 core subunit proteins in different eukaryotic supergroups with emphasis on the early-diverged lineages and explore the molecular evolution of PRC2 subunits by phylogenetics. For the first time, we identify the putative ortholog of E(z) in Discoba, a lineage hypothetically proximal to the eukaryotic root, strongly supporting emergence of PRC2 before the diversification of eukaryotes. Analyzing 283 species, we robustly detect a common presence of E(z) and ESC, indicating a conserved functional core. Full-length Su(z)12 orthologs were identified in some lineages and species only, indicating, nonexclusively, high divergence of VEFS-Box–containing Su(z)12-like proteins, functional convergence of sequence-unrelated proteins, or Su(z)12 dispensability. Our results trace E(z) evolution within the SET-domain protein family, proposing a substrate specificity shift during E(z) evolution based on SET-domain and H3 histone interaction prediction.

Identification and analysis of sucrose synthase gene family associated with polysaccharide biosynthesis in Dendrobium catenatum by transcriptomic analysis

Background

Dendrobium catenatum is a valuable traditional medicinal herb with high commercial value. D. catenatum stems contain abundant polysaccharides which are one of the main bioactive components. However, although some genes related to the synthesis of the polysaccharides have been reported, more key genes need to be further elucidated.

Results

In this study, the contents of polysaccharides and mannose in D. catenatum stems at four developmental stages were compared, and the stems' transcriptomes were analyzed to explore the synthesis mechanism of the polysaccharides. Many genes involved in starch and sucrose metabolisms were identified by KEGG pathway analysis. Further analysis found that sucrose synthase (SUS; EC 2.4.1.13) gene maybe participated in the polysaccharide synthesis. Hence, we further investigated the genomic characteristics and evolution relationships of the SUS family in plants. The result suggested that the SUS gene of D. catenatum (DcSUS) had undergone the expansion characterized by tandem duplication which might be related to the enrichment of the polysaccharides in D. catenatum stems. Moreover, expression analyses of the DcSUS displayed significant divergent patterns in different tissues and could be divided into two main groups in the stems with four developmental stages.

Conclusion

In general, our results revealed that DcSUS is likely involved in the metabolic process of the stem polysaccharides, providing crucial clues for exploiting the key genes associated with the polysaccharide synthesis.

Comprehensive Analysis of the SUV Gene Family in Allopolyploid Brassica napus and Its Diploid Ancestors

SUV (the Suppressor of variegation [Su(var)] homologs and related) gene family is a subgroup of the SET gene family. According to the SRA domain and WIYLD domain distributions, it can be divided into two categories, namely SUVH (the Suppressor of variegation [Su(var)] homologs) and SUVR (the Suppressor of variegation [Su(var)] related). In this study, 139 SUV genes were identified in allopolyploid Brassica napus and its diploid ancestors, and their evolutionary relationships, protein properties, gene structures, motif distributions, transposable elements, cis-acting elements and gene expression patterns were analyzed. Our results showed that the SUV gene family of B. napus was amplified during allopolyploidization, in which the segmental duplication and TRD played critical roles. After the separation of Brassica and Arabidopsis lineages, orthologous gene analysis showed that many SUV genes were lost during the evolutionary process in B. rapa, B. oleracea and B. napus. The analysis of the gene and protein structures and expression patterns of 30 orthologous gene pairs which may have evolutionary relationships showed that most of them were conserved in gene structures and protein motifs, but only four gene pairs had the same expression patterns.

The Natural Antisense Transcript DONE40 Derived from the lncRNA ENOD40 Locus Interacts with SET Domain Protein ASHR3 During Inception of Symbiosis in Arachis hypogaea

The long noncoding RNA ENOD40 is required for cortical cell division during root nodule symbiosis (RNS) of legumes, though it is not essential for actinorhizal RNS. Our objective was to understand whether ENOD40 was required for aeschynomenoid nodule formation in Arachis hypogaea. AhENOD40 express from chromosome 5 (chr5) (AhENOD40-1) and chr15 (AhENOD40-2) during symbiosis, and RNA interference of these transcripts drastically affected nodulation, indicating the importance of ENOD40 in A. hypogaea. Furthermore, we demonstrated several distinct characteristics of ENOD40. (i) Natural antisense transcript (NAT) of ENOD40 was detected from the AhENOD40-1 locus (designated as NAT-AhDONE40). (ii) Both AhENOD40-1 and AhENOD40-2 had two exons, whereas NAT-AhDONE40 was monoexonic. Reverse-transcription quantitative PCR analysis indicated both sense and antisense transcripts to be present in both cytoplasm and nucleus, and their expression increased with the progress of symbiosis. (iii) RNA pull-down from whole cell extracts of infected roots at 4 days postinfection indicated NAT-AhDONE40 to interact with the SET (Su(var)3-9, enhancer of Zeste and Trithorax) domain containing absent small homeotic disc (ASH) family protein AhASHR3 and this interaction was further validated using RNA immunoprecipitation and electrophoretic mobility shift assay. (iv) Chromatin immunoprecipitation assays indicate deposition of ASHR3-specific histone marks H3K36me3 and H3K4me3 in both of the ENOD40 loci during the progress of symbiosis. ASHR3 is known for its role in optimizing cell proliferation and reprogramming. Because both ASHR3 and ENOD40 from legumes cluster away from those in actinorhizal plants and other nonlegumes in phylogenetic distance trees, we hypothesize that the interaction of DONE40 with ASHR3 could have evolved for adapting the nodule organogenesis program for legumes.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

A single amino acid residue substitution in BraA04g017190.3C, a histone methyltransferase, results in premature bolting in Chinese cabbage (Brassica rapa L. ssp. Pekinensis)

BACKGROUND

Flowering is an important inflection point in the transformation from vegetative to reproductive growth, and premature bolting severely decreases crop yield and quality.

RESULTS

In this study, a stable early-bolting mutant, ebm3, was identified in an ethyl methanesulfonate (EMS)-mutagenized population of a Chinese cabbage doubled haploid (DH) line 'FT'. Compared with 'FT', ebm3 showed early bolting under natural cultivation in autumn, and curled leaves. Genetic analysis showed that the early-bolting phenotype was controlled by a single recessive nuclear gene. Modified MutMap sequencing, genotyping analyses and allelism test provide strong evidence that BrEBM3 (BraA04g017190.3 C), encoding the histone methyltransferase CURLY LEAF (CLF), was the strongly candidate gene of the emb3. A C to T base substitution in the 14th exon of BrEBM3 resulted in an amino acid change (S to F) and the early-bolting phenotype of emb3. The mutation occurred in the SET domain (Suppressor of protein-effect variegation 3-9, Enhancer-of-zeste, Trithorax), which catalyzes site- and state-specific lysine methylation in histones. Tissue-specific expression analysis showed that BrEBM3 was highly expressed in the flower and bud. Promoter activity assay confirmed that BrEBM3 promoter was active in inflorescences. Subcellular localization analysis revealed that BrEBM3 localized in the nucleus. Transcriptomic studies supported that BrEBM3 mutation might repress H3K27me3 deposition and activate expression of the AGAMOUS (AG) and AGAMOUS-like (AGL) loci, resulting in early flowering.

CONCLUSIONS

Our study revealed that an EMS-induced early-bolting mutant ebm3 in Chinese cabbage was caused by a nonsynonymous mutation in BraA04g017190.3 C, encoding the histone methyltransferase CLF. These results improve our knowledge of the genetic and genomic resources of bolting and flowering, and may be beneficial to the genetic improvement of Chinese cabbage.

Computational Identification of Functional Centers in Complex Proteins: A Step-by-Step Guide With Examples

In proteins, functional centers consist of the key amino acids required to perform molecular functions such as catalysis, ligand-binding, hormone- and gas-sensing. These centers are often embedded within complex multi-domain proteins and can perform important cellular signaling functions that enable fine-tuning of temporal and spatial regulation of signaling molecules and networks. To discover hidden functional centers, we have developed a protocol that consists of the following sequential steps. The first is the assembly of a search motif based on the key amino acids in the functional center followed by querying proteomes of interest with the assembled motif. The second consists of a structural assessment of proteins that harbor the motif. This approach, that relies on the application of computational tools for the analysis of data in public repositories and the biological interpretation of the search results, has to-date uncovered several novel functional centers in complex proteins. Here, we use recent examples to describe a step-by-step guide that details the workflow of this approach and supplement with notes, recommendations and cautions to make this protocol robust and widely applicable for the discovery of hidden functional centers.

Methyltransferase SET domain family and its relationship with cardiovascular development and diseases

Abnormal epigenetic modification is closely related to the occurrence and development of cardiovascular diseases. The SET domain (SETD) family is an important epigenetic modifying enzyme containing SETD. They mainly affect gene expression by methylating H3K4, H3K9, H3K36 and H4K20. Additionally, the SETD family catalyzes the methylation of non-histone proteins, thereby affects the signal transduction of signal transduction and activator of transcription (STAT) 1, Wnt/β-catenin, hypoxia-inducible factor (HIF)-1α and Hippo/YAP pathways. The SETD family has the following regulatory effects on cardiovascular development and diseases: regulating coronary artery formation and cardiac development; protecting cardiac tissue from ischemia reperfusion injury; regulating inflammation, oxidative stress and apoptosis in cardiovascular complications of diabetes; participating in the formation of pulmonary hypertension; regulating thrombosis, cardiac hypertrophy and arrhythmia. This article summarizes the basic structures, expression regulation mechanisms and the role of existing SETD family members in cardiovascular development and diseases, in order to provide a basis for understanding the molecular mechanism of cardiovascular disease and exploring the therapeutic targets.

The ancient wave of polyploidization events in flowering plants and their facilitated adaptation to environmental stress

Flowering plants, or angiosperms, consist of more than 300,000 species, far more than any other land plant lineages. The accumulated evidence indicates that multiple ancient polyploidy events occurred around 100 to 120 million years ago during the Cretaceous and drove the early diversification of four major clades of angiosperms: gamma whole-genome triplication in the common ancestor of core eudicots, tau whole-genome duplication during the early diversification of monocots, lambda whole-genome duplication during the early diversification of magnoliids, and pi whole-genome duplication in the Nymphaeales lineage. These four polyploidy events have played essential roles in the adaptive evolution and diversification of major clades of flowering plants. Here, we specifically review the current understanding of this wave of ancient whole-genome duplications and their evolutionary significance. Notably, although these ancient whole-genome duplications occurred independently, they have contributed to the expansion of many stress-related genes (e.g., heat shock transcription factors and Arabidopsis response regulators)，and these genes could have been selected for by global environmental changes in the Cretaceous. Therefore, this ancient wave of paleopolyploidy events could have significantly contributed to the adaptation of angiosperms to environmental changes, and potentially promoted the wide diversification of flowering plants.

Writing and Reading Histone H3 Lysine 9 Methylation in Arabidopsis

In eukaryotes, histone H3 lysine 9 methylation (H3K9me) mediates the silencing of invasive and repetitive sequences by preventing the expression of aberrant gene products and the activation of transposition. In Arabidopsis, while it is well known that dimethylation of histone H3 at lysine 9 (H3K9me2) is maintained through a feedback loop between H3K9me2 and DNA methylation, the details of the H3K9me2-dependent silencing pathway have not been fully elucidated. Recently, the regulation and the function of H3K9 methylation have been extensively characterized. In this review, we summarize work from the recent studies regarding the regulation of H3K9me2, emphasizing the process of deposition and reading and the biological significance of H3K9me2 in Arabidopsis.

The function of histone lysine methylation related SET domain group proteins in plants

Histone methylation, which is mediated by the histone lysine (K) methyltransferases (HKMTases), is a mechanism associated with many pathways in eukaryotes. Most HKMTases have a conserved SET (Su(var) 3-9,E(z),Trithorax) domain, while the HKMTases with SET domains are called the SET domain group (SDG) proteins. In plants, only SDG proteins can work as HKMTases. In this review, we introduced the classification of SDG family proteins in plants and the structural characteristics of each subfamily, surmise the functions of SDG family members in plant growth and development processes, including pollen and female gametophyte development, flowering, plant morphology and the responses to stresses. This review will help researchers better understand the SDG proteins and histone methylation in plants and lay a basic foundation for further studies on SDG proteins.

Protein methylome analysis in Arabidopsis reveals regulation in RNA-related processes

Protein methylation has been proposed as an important post-translational modification, which occurs predominantly on lysine and arginine residues. Recent discoveries have revealed that protein methylation is also present on non-histones besides histones, and plays critical roles in regulating protein stability and function. However, proteome-wide identification of methylated proteins in plants remains unexplored. Here, we present the first global survey of monomethyl arginine, symmetric and asymmetric dimethyl arginine, and monomethyl, dimethyl, trimethyl lysine modifications in the proteomes of 10-day-old Arabidopsis seedlings through a combination of immunoaffinity purification and mass spectrometry analysis. In total, we identified 617 methylation sites which mapped to 412 proteins, with 263 proteins harboring 381 lysine methylation sites and 149 proteins harboring 236 arginine methylation sites. Among them, 607 methylation sites on 408 proteins were novel findings. Motif analysis revealed that glycine preferentially flanked methylated arginine residues, whereas aspartate and glutamate enriched around mono- and dimethylated lysine sites. Methylated proteins were involved in a variety of metabolic processes, showing significant enrichment in RNA-related metabolic pathways including spliceosome, RNA transport, and ribosome. Our data provide a global view of methylated non-histone proteins in Arabidopsis, laying foundations for elucidating the biological function of protein methylation in plants. SIGNIFICANCE: Protein methylation has emerged as a common and important modification both in eukaryotes and prokaryotes. The identification of methylated sites/peptides is fundamental for further functional analysis of protein methylation. This study was the first proteome-scale identification of lysine and arginine methylation in plants. We found that methylation occurred widely on non-histone proteins in Arabidopsis and was involved in diverse biological functions. The results provide foundations for the investigation of the protein methylome in Arabidopsis and provide powerful resources for the functional analysis of protein methylation in plants.

Comparative and evolutionary analyses of the divergence of plant oligosaccharyltransferase STT3 isoforms

STT3 is a catalytic subunit of hetero-oligomeric oligosaccharyltransferase (OST), which is important for asparagine-linked glycosylation. In mammals and plants, OSTs with different STT3 isoforms exhibit distinct levels of enzymatic efficiency or different responses to stressors. Although two different STT3 isoforms have been identified in both plants and animals, it remains unclear whether these isoforms result from gene duplication in an ancestral eukaryote. Furthermore, the molecular mechanisms underlying the functional divergences between the two STT3 isoforms in plant have not been well elucidated. Here, we conducted phylogenetic analysis of the major evolutionary node species and suggested that gene duplications of STT3 may have occurred independently in animals and plants. Across land plants, the exon-intron structure differed between the two STT3 isoforms, but was highly conserved for each isoform. Most angiosperm STT3a genes had 23 exons with intron phase 0, while STT3b genes had 6 exons with intron phase 2. Characteristic motifs (motif 18 and 19) of STT3s were mapped to different structure domains in the plant STT3 proteins. These two motifs overlap with regions of high nonsynonymous-to-synonymous substitution rates, suggesting the regions may be related to functional difference between STT3a and STT3b. In addition, promoter elements and gene expression profiles were different between the two isoforms, indicating expression pattern divergence of the two genes. Collectively, the identified differences may result in the functional divergence of plant STT3s.

New Perspectives on Plant Adenylyl Cyclases

It is increasingly clear that plant genomes encode numerous complex multidomain proteins that harbor functional adenylyl cyclase (AC) centers. These AC containing proteins have well-documented roles in development and responses to the environment. However, it is only for a few of these proteins that we are beginning to understand the intramolecular mechanisms that govern their cellular and biological functions, as detailed characterizations are biochemically and structurally challenging given that these poorly conserved AC centers typically constitute only a small fraction (<10%) of complex plant proteins. Here, we offer fresh perspectives on their seemingly cryptic activities specifically showing evidence for the presence of multiple functional AC centers in a single protein and linking their catalytic strengths to the Mg2+/Mn2+-binding amino acids. We used a previously described computational approach to identify candidate multidomain proteins from Arabidopsis thaliana that contain multiple AC centers and show, using an Arabidopsis leucine-rich repeat containing protein (TAIR ID: At3g14460; AtLRRAC1) as example, biochemical evidence for multienzymatic activities. Importantly, all AC-containing fragments of this protein can complement the AC-deficient mutant cyaA in Escherichia coli, while structural modeling coupled with molecular docking simulations supports catalytic feasibility albeit to varying degrees as determined by the frequency of suitable substrate binding poses predicted for the AC sites. This statistic correlates well with the enzymatic assays, which implied that the greatly reduced AC activities is due to the absence of the negatively charged [DE] amino acids previously assigned to cation-, in particular Mg2+/Mn2+-binding roles in ACs.

Engineering meiotic recombination pathways in rice

In the last 15 years, outstanding progress has been made in understanding the function of meiotic genes in the model dicot and monocot plants Arabidopsis and rice (Oryza sativa L.), respectively. This knowledge allowed to modulate meiotic recombination in Arabidopsis and, more recently, in rice. For instance, the overall frequency of crossovers (COs) has been stimulated 2.3- and 3.2-fold through the inactivation of the rice FANCM and RECQ4 DNA helicases, respectively, two genes involved in the repair of DNA double-strand breaks (DSBs) as noncrossovers (NCOs) of the Class II crossover pathway. Differently, the programmed induction of DSBs and COs at desired sites is currently explored by guiding the SPO11-1 topoisomerase-like transesterase, initiating meiotic recombination in all eukaryotes, to specific target regions of the rice genome. Furthermore, the inactivation of 3 meiosis-specific genes, namely PAIR1, OsREC8 and OsOSD1, in the Mitosis instead of Meiosis (MiMe) mutant turned rice meiosis into mitosis, thereby abolishing recombination and achieving the first component of apomixis, apomeiosis. The successful translation of Arabidopsis results into a crop further allowed the implementation of two breakthrough strategies that triggered parthenogenesis from the MiMe unreduced clonal egg cell and completed the second component of diplosporous apomixis. Here, we review the most recent advances in and future prospects of the manipulation of meiotic recombination in rice and potentially other major crops, all essential for global food security.

Arabidopsis S2Lb links AtCOMPASS-like and SDG2 activity in H3K4me3 independently from histone H2B monoubiquitination

Background

The functional determinants of H3K4me3, their potential dependency on histone H2B monoubiquitination, and their contribution to defining transcriptional regimes are poorly defined in plant systems. Unlike in Saccharomyces cerevisiae, where a single SET1 protein catalyzes H3K4me3 as part of COMPlex of proteins ASsociated with Set1 (COMPASS), in Arabidopsis thaliana, this activity involves multiple histone methyltransferases. Among these, the plant-specific SET DOMAIN GROUP 2 (SDG2) has a prominent role.

Results

We report that SDG2 co-regulates hundreds of genes with SWD2-like b (S2Lb), a plant ortholog of the Swd2 axillary subunit of yeast COMPASS. We show that S2Lb co-purifies with the AtCOMPASS core subunit WDR5, and both S2Lb and SDG2 directly influence H3K4me3 enrichment over highly transcribed genes. S2Lb knockout triggers pleiotropic developmental phenotypes at the vegetative and reproductive stages, including reduced fertility and seed dormancy. However, s2lb seedlings display little transcriptomic defects as compared to the large repertoire of genes targeted by S2Lb, SDG2, or H3K4me3, suggesting that H3K4me3 enrichment is important for optimal gene induction during cellular transitions rather than for determining on/off transcriptional status. Moreover, unlike in budding yeast, most of the S2Lb and H3K4me3 genomic distribution does not rely on a trans-histone crosstalk with histone H2B monoubiquitination.

Conclusions

Collectively, this study unveils that the evolutionarily conserved COMPASS-like complex has been co-opted by the plant-specific SDG2 histone methyltransferase and mediates H3K4me3 deposition through an H2B monoubiquitination-independent pathway in Arabidopsis.

Electronic supplementary material

The online version of this article (10.1186/s13059-019-1705-4) contains supplementary material, which is available to authorized users.

MORC Domain Definition and Evolutionary Analysis of the MORC Gene Family in Green Plants

Microrchidia (MORC) proteins have been described as epigenetic regulators and plant immune mediators in Arabidopsis. Typically, plant and animal MORC proteins contain a hallmark GHKL-type (Gyrase, Hsp90, Histidine kinase, MutL) ATPase domain in their N-terminus. Here, 356 and 83 MORC orthologues were identified in 60 plant and 27 animal genomes. Large-scale MORC sequence analyses revealed the presence of a highly conserved motif composition that defined as the MORC domain. The MORC domain was present in both plants and animals, indicating that it originated in the common ancestor before the divergence of plants and animals. Phylogenetic analyses showed that MORC genes in both plant and animal lineages were clearly classified into two major groups, named Plants-Group I, Plants-Group II and Animals-Group I, Animals-Group II, respectively. Further analyses of MORC genes in green plants uncovered that Group I can be subdivided into Group I-1 and Group I-2. Group I-1 only contains seed plant genes, suggesting that Group I-1 and I-2 divergence occurred at least before the emergence of spermatophytes. Group I-2 and Group II have undergone several gene duplications, resulting in the expansion of MORC gene family in angiosperms. Additionally, MORC gene expression analyses in Arabidopsis, soybean, and rice revealed a higher expression level in reproductive tissues compared with other organs, and showed divergent expression patterns for several paralogous gene pairs. Our studies offered new insights into the origins, phylogenetic relationships, and expressional patterns of MORC family members in green plants, which would help to further reveal their functions as plant epigenetic regulators.

realDB: a genome and transcriptome resource for the red algae (phylum Rhodophyta)

With over 6000 species in seven classes, red algae (Rhodophyta) have diverse economic, ecological, experimental and evolutionary values. However, red algae are usually absent or rare in comparative analyses because genomic information of this phylum is often under-represented in various comprehensive genome databases. To improve the accessibility to the ome data and omics tools for red algae, we provided 10 genomes and 27 transcriptomes representing all seven classes of Rhodophyta. Three genomes and 18 transcriptomes were de novo assembled and annotated in this project. User-friendly BLAST suit, Jbrowse tools and search system were developed for online analyses. Detailed introductions to red algae taxonomy and the sequencing status are also provided. In conclusion, realDB (realDB.algaegenome.org) provides a platform covering the most genome and transcriptome data for red algae and a suite of tools for online analyses, and will attract both red algal biologists and those working on plant ecology, evolution and development.

Database URL: http://realdb.algaegenome.org/

The Lysine Demethylase dKDM2 Is Non-essential for Viability, but Regulates Circadian Rhythms in Drosophila

Post-translational modification of histones, such as histone methylation controlled by specific methyltransferases and demethylases, play critical roles in modulating chromatin dynamics and transcription in eukaryotes. Misregulation of histone methylation can lead to aberrant gene expression, thereby contributing to abnormal development and diseases such as cancer. As such, the mammalian lysine-specific demethylase 2 (KDM2) homologs, KDM2A and KDM2B, are either oncogenic or tumor suppressive depending on specific pathological contexts. However, the role of KDM2 proteins during development remains poorly understood. Unlike vertebrates, Drosophila has only one KDM2 homolog (dKDM2), but its functions in vivo remain elusive due to the complexities of the existing mutant alleles. To address this problem, we have generated two dKdm2 null alleles using the CRISPR/Cas9 technique. These dKdm2 homozygous mutants are fully viable and fertile, with no developmental defects observed under laboratory conditions. However, the dKdm2 null mutant adults display defects in circadian rhythms. Most of the dKdm2 mutants become arrhythmic under constant darkness, while the circadian period of the rhythmic mutant flies is approximately 1 h shorter than the control. Interestingly, lengthened circadian periods are observed when dKDM2 is overexpressed in circadian pacemaker neurons. Taken together, these results demonstrate that dKdm2 is not essential for viability; instead, dKDM2 protein plays important roles in regulating circadian rhythms in Drosophila. Further analyses of the molecular mechanisms of dKDM2 and its orthologs in vertebrates regarding the regulation of circadian rhythms will advance our understanding of the epigenetic regulations of circadian clocks.

An outlook on lysine methylation of non-histone proteins in plants

Protein methylation is a very diverse, widespread, and important post-translational modification affecting all aspects of cellular biology in eukaryotes. Methylation on the side-chain of lysine residues in histones has received considerable attention due to its major role in determining chromatin structure and the epigenetic regulation of gene expression. Over the last 20 years, lysine methylation of non-histone proteins has been recognized as a very common modification that contributes to the fine-tuned regulation of protein function. In plants, our knowledge in this field is much more fragmentary than in yeast and animal cells. In this review, we describe the plant enzymes involved in the methylation of non-histone substrates, and we consider historical and recent advances in the identification of non-histone lysine-methylated proteins in photosynthetic organisms. Finally, we discuss our current knowledge about the role of protein lysine methylation in regulating molecular and cellular functions in plants, and consider challenges for future research.

Comparative analysis of plant MKK gene family reveals novel expansion mechanism of the members and sheds new light on functional conservation

Background

Mitogen-activated protein kinase (MAPK) cascades play critical functions in almost every aspect of plant growth and development, which regulates many physiological and biochemical processes. As a middle nodal point of the MAPK cascades, although evolutionary analysis of MKK from individual plant families had some reports, their evolutionary history in entire plants is still not clear.

Results

To better understand the evolution and function of plant MKKs, we performed systematical molecular evolutionary analysis of the MAPKK gene family and also surveyed their gene organizations, sequence features and expression patterns in different subfamilies. Phylogenetic analysis showed that plant MAPKK fall into five different groups (Group A–E). Majority orthology groups seemed to be a single or low-copy genes in all plant species analyzed in Group B, C and D, whereas group A MKKs undergo several duplication events, generating multiple gene copies. Further analysis showed that these duplication events were on account of whole genome duplications (WGDs) in plants and the duplicate genes maybe have undergone functional divergence. We also found that group E MKKs had mutation with one change of serine or theronine might lead to inactivity originated through the ancient tandem duplicates in monocots. Moreover, we also identified MKK3 integrated NTF2 domain that might have gradually lost the cytoplasmic-nuclear trafficking activity, which suggests that they may involve with the gene function more and more sophistication in the evolutionary process. Moreover, expression analyses indicated that plant MKK genes play probable roles in UV-B signaling.

Conclusion

In general, ancient gene and genome duplications are significantly conducive to the expansion of the plant MKK gene family. Our study reveals two distinct evolutionary patterns for plant MKK proteins and sheds new light on the functional evolution of this gene family.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4793-8) contains supplementary material, which is available to authorized users.

Comparative genomic analysis of SET domain family reveals the origin, expansion, and putative function of the arthropod-specific SmydA genes as histone modifiers in insects

The SET domain is an evolutionarily conserved motif present in histone lysine methyltransferases, which are important in the regulation of chromatin and gene expression in animals. In this study, we searched for SET domain–containing genes (SET genes) in all of the 147 arthropod genomes sequenced at the time of carrying out this experiment to understand the evolutionary history by which SET domains have evolved in insects. Phylogenetic and ancestral state reconstruction analysis revealed an arthropod-specific SET gene family, named SmydA, that is ancestral to arthropod animals and specifically diversified during insect evolution. Considering that pseudogenization is the most probable fate of the new emerging gene copies, we provided experimental and evolutionary evidence to demonstrate their essential functions. Fluorescence in situ hybridization analysis and in vitro methyltransferase activity assays showed that the SmydA-2 gene was transcriptionally active and retained the original histone methylation activity. Expression knockdown by RNA interference significantly increased mortality, implying that the SmydA genes may be essential for insect survival. We further showed predominantly strong purifying selection on the SmydA gene family and a potential association between the regulation of gene expression and insect phenotypic plasticity by transcriptome analysis. Overall, these data suggest that the SmydA gene family retains essential functions that may possibly define novel regulatory pathways in insects. This work provides insights into the roles of lineage-specific domain duplication in insect evolution.

Widespread Whole Genome Duplications Contribute to Genome Complexity and Species Diversity in Angiosperms

Gene duplications provide evolutionary potentials for generating novel functions, while polyploidization or whole genome duplication (WGD) doubles the chromosomes initially and results in hundreds to thousands of retained duplicates. WGDs are strongly supported by evidence commonly found in many species-rich lineages of eukaryotes, and thus are considered as a major driving force in species diversification. We performed comparative genomic and phylogenomic analyses of 59 public genomes/transcriptomes and 46 newly sequenced transcriptomes covering major lineages of angiosperms to detect large-scale gene duplication events by surveying tens of thousands of gene family trees. These analyses confirmed most of the previously reported WGDs and provided strong evidence for novel ones in many lineages. The detected WGDs supported a model of exponential gene loss during evolution with an estimated half-life of approximately 21.6 million years, and were correlated with both the emergence of lineages with high degrees of diversification and periods of global climate changes. The new datasets and analyses detected many novel WGDs widely spread during angiosperm evolution, uncovered preferential retention of gene functions in essential cellular metabolisms, and provided clues for the roles of WGD in promoting angiosperm radiation and enhancing their adaptation to environmental changes.

Discovery of Novel Functional Centers With Rationally Designed Amino Acid Motifs

Plants are constantly exposed to environmental stresses and in part due to their sessile nature, they have evolved signal perception and adaptive strategies that are distinct from those of other eukaryotes. This is reflected at the cellular level where receptors and signalling molecules cannot be identified using standard homology-based searches querying with proteins from prokaryotes and other eukaryotes. One of the reasons for this is the complex domain architecture of receptor molecules. In order to discover hidden plant signalling molecules, we have developed a motif-based approach designed specifically for the identification of functional centers in plant molecules. This has made possible the discovery of novel components involved in signalling and stimulus-response pathways; the molecules include cyclic nucleotide cyclases, a nitric oxide sensor and a novel target for the hormone abscisic acid. Here, we describe the major steps of the method and illustrate it with recent and experimentally confirmed molecules as examples. We foresee that carefully curated search motifs supported by structural and bioinformatic assessments will uncover many more structural and functional aspects, particularly of signalling molecules.

Phylogenetic relationship and domain organisation of SET domain proteins of Archaeplastida

BACKGROUND

SET is a conserved protein domain with methyltransferase activity. Several genome and transcriptome data in plant lineage (Archaeplastida) are available but status of SET domain proteins in most of the plant lineage is not comprehensively analysed.

RESULTS

In this study phylogeny and domain organisation of 506 computationally identified SET domain proteins from 16 members of plant lineage (Archaeplastida) are presented. SET domain proteins of rice and Arabidopsis are used as references. This analysis revealed conserved as well as unique features of SET domain proteins in Archaeplastida. SET domain proteins of plant lineage can be categorised into five classes- E(z), Ash, Trx, Su(var) and Orphan. Orphan class of SET proteins contain unique domains predominantly in early Archaeplastida. Contrary to previous study, this study shows first appearance of several domains like SRA on SET domain proteins in chlorophyta instead of bryophyta.

CONCLUSION

The present study is a framework to experimentally characterize SET domain proteins in plant lineage.

Analysis of the meiotic transcriptome reveals the genes related to the regulation of pollen abortion in cytoplasmic male-sterile pepper (Capsicum annuum L.)

CMS, which refers to the inability to generate functional pollen grains while still producing a normal gynoecium, has been widely used for pepper hybrid seed production. Pepper line 8214A is an excellent CMS line exhibiting 100% male sterility and superior economic characteristics. A TUNEL assay revealed the nuclear DNA is damaged in 8214A PMCs during meiosis. TEM images indicated that the 8214A PMCs exhibited asynchronous meiosis after prophase I, and some PMCs degraded prematurely with morphological features typical of PCD. Additionally, at the end of meiosis, the 8214A PMCs formed abnormal non-tetrahedral tetrads that degraded in situ. To identify the genes involved in the pollen abortion of line 8214A, the transcriptional profiles of the 8214A and the 8214B anthers (i.e., from the fertile maintainer line) during meiosis were analyzed using an RNA-seq approach. A total of 1355 genes were determined to be differentially expressed, including 424 and 931 up- and down- regulated genes, respectively, in the 8214A anthers during meiosis relative to the expression levels in the 8214B. The expression levels of ubiquitin ligase and cell cycle-related genes were apparently down-regulated, while the expression of methyltransferase genes was up-regulated in the 8214A anthers during meiosis, which likely contributed to the PCD of these PMCs during meiosis. Thus, our results may be useful for revealing the molecular mechanism regulating the pollen abortion of CMS pepper.

High-Resolution Mapping of Crossover Events in the Hexaploid Wheat Genome Suggests a Universal Recombination Mechanism

During meiosis, crossovers (COs) create new allele associations by reciprocal exchange of DNA. In bread wheat (Triticum aestivum L.), COs are mostly limited to subtelomeric regions of chromosomes, resulting in a substantial loss of breeding efficiency in the proximal regions, though these regions carry ∼60-70% of the genes. Identifying sequence and/or chromosome features affecting recombination occurrence is thus relevant to improve and drive recombination. Using the recent release of a reference sequence of chromosome 3B and of the draft assemblies of the 20 other wheat chromosomes, we performed fine-scale mapping of COs and revealed that 82% of COs located in the distal ends of chromosome 3B representing 19% of the chromosome length. We used 774 SNPs to genotype 180 varieties representative of the Asian and European genetic pools and a segregating population of 1270 F₆ lines. We observed a common location for ancestral COs (predicted through linkage disequilibrium) and the COs derived from the segregating population. We delineated 73 small intervals (<26 kb) on chromosome 3B that contained 252 COs. We observed a significant association of COs with genic features (73 and 54% in recombinant and nonrecombinant intervals, respectively) and with those expressed during meiosis (67% in recombinant intervals and 48% in nonrecombinant intervals). Moreover, while the recombinant intervals contained similar amounts of retrotransposons and DNA transposons (42 and 53%), nonrecombinant intervals had a higher level of retrotransposons (63%) and lower levels of DNA transposons (28%). Consistent with this, we observed a higher frequency of a DNA motif specific to the TIR-Mariner DNA transposon in recombinant intervals.

SETD4 Regulates Cell Quiescence and Catalyzes the Trimethylation of H4K20 during Diapause Formation in Artemia

As a prominent characteristic of cell life, the regulation of cell quiescence is important for proper development, regeneration, and stress resistance and may play a role in certain degenerative diseases. However, the mechanism underlying quiescence remains largely unknown. Encysted embryos of Artemia are useful for studying the regulation of this state because they remain quiescent for prolonged periods during diapause, a state of obligate dormancy. In the present study, SET domain-containing protein 4, a histone lysine methyltransferase from Artemia, was identified, characterized, and named Ar-SETD4. We found that Ar-SETD4 was expressed abundantly in Artemia diapause embryos, in which cells were in a quiescent state. Meanwhile, trimethylated histone H4K20 (H4K20me3) was enriched in diapause embryos. The knockdown of Ar-SETD4 reduced the level of H4K20me3 significantly and prevented the formation of diapause embryos in which neither the cell cycle nor embryogenesis ceased. The catalytic activity of Ar-SETD4 on H4K20me3 was confirmed by an in vitro histone methyltransferase (HMT) assay and overexpression in cell lines. This study provides insights into the function of SETD4 and the mechanism of cell quiescence regulation.

Genome-Wide Analysis of Soybean JmjC Domain-Containing Proteins Suggests Evolutionary Conservation Following Whole-Genome Duplication

Histone modifications, such as methylation and demethylation, play an important role in regulating chromatin structure and gene expression. The JmjC domain-containing proteins, an important family of histone lysine demethylases (KDMs), play a key role in maintaining homeostasis of histone methylation in vivo. In this study, we performed a comprehensive analysis of the jumonji C (JmjC) gene family in the soybean genome and identified 48 JmjC genes (GmJMJs) distributed unevenly across 18 chromosomes. Phylogenetic analysis showed that these JmjC domain-containing genes can be divided into eight groups. GmJMJs within the same phylogenetic group share similar exon/intron organization and domain composition. In addition, 16 duplicated gene pairs were formed by a Glycine-specific whole-genome duplication (WGD) event approximately 13 million years ago (Mya). By investigating the expression profiles of these gene pairs in various tissues, we showed that the expression pattern is conserved in the polyploidy-derived JmjC duplicates, demonstrating that the majority of GmJMJs were preferentially retained after the most recent WGD event and suggesting important roles for demethylase duplications in soybean evolution. These results shed light on the evolutionary history of this family in soybean and provide insights into the JmjCs which will be helpful to reveal their functions in controlling soybean development.

Identification of SET Domain-Containing Proteins in Gossypium raimondii and Their Response to High Temperature Stress

SET (Su(var), E(z), and Trithorax) domain-containing proteins play an important role in plant development and stress responses through modifying lysine methylation status of histone. Gossypium raimondii may be the putative contributor of the D-subgenome of economical crops allotetraploid G. hirsutum and G. barbadense and therefore can potentially provide resistance genes. In this study, we identified 52 SET domain-containing genes from G. raimondii genome. Based on conserved sequences, these genes are grouped into seven classes and are predicted to catalyze the methylation of different substrates: GrKMT1 for H3K9me, GrKMT2 and GrKMT7 for H3K4me, GrKMT3 for H3K36me, GrKMT6 for H3K27me, but GrRBCMT and GrS-ET for nonhistones substrate-specific methylation. Seven pairs of GrKMT and GrRBCMT homologous genes are found to be duplicated, possibly one originating from tandem duplication and five from a large scale or whole genome duplication event. The gene structure, domain organization and expression patterns analyses suggest that these genes’ functions are diversified. A few of GrKMTs and GrRBCMTs, especially for GrKMT1A;1a, GrKMT3;3 and GrKMT6B;1 were affected by high temperature (HT) stress, demonstrating dramatically changed expression patterns. The characterization of SET domain-containing genes in G. raimondii provides useful clues for further revealing epigenetic regulation under HT and function diversification during evolution.

Identification and characterization of histone lysine methylation modifiers in Fragaria vesca

The diploid woodland strawberry (Fragaria vesca) is an important model for fruit crops because of several unique characteristics including the small genome size, an ethylene-independent fruit ripening process, and fruit flesh derived from receptacle tissues rather than the ovary wall which is more typical of fruiting plants. Histone methylation is an important factor in gene regulation in higher plants but little is known about its roles in fruit development. We have identified 45 SET methyltransferase, 22 JmjC demethylase and 4 LSD demethylase genes in F. vesca. The analysis of these histone modifiers in eight plant species supports the clustering of those genes into major classes consistent with their functions. We also provide evidence that whole genome duplication and dispersed duplications via retrotransposons may have played pivotal roles in the expansion of histone modifier genes in F. vesca. Furthermore, transcriptome data demonstrated that expression of some SET genes increase as the fruit develops and peaks at the turning stage. Meanwhile, we have observed that expression of those SET genes responds to cold and heat stresses. Our results indicate that regulation of histone methylation may play a critical role in fruit development as well as responses to abiotic stresses in strawberry.

Genome-Wide Identification, Classification, and Expression Analysis of Amino Acid Transporter Gene Family in Glycine Max

Amino acid transporters (AATs) play important roles in transporting amino acid across cellular membranes and are essential for plant growth and development. To date, the AAT gene family in soybean (Glycine max L.) has not been characterized. In this study, we identified 189 AAT genes from the entire soybean genomic sequence, and classified them into 12 distinct subfamilies based upon their sequence composition and phylogenetic positions. To further investigate the functions of these genes, we analyzed the chromosome distributions, gene structures, duplication patterns, phylogenetic tree, tissue expression patterns of the 189 AAT genes in soybean. We found that a large number of AAT genes in soybean were expanded via gene duplication, 46 and 36 GmAAT genes were WGD/segmental and tandemly duplicated, respectively. Further comprehensive analyses of the expression profiles of GmAAT genes in various stages of vegetative and reproductive development showed that soybean AAT genes exhibited preferential or distinct expression patterns among different tissues. Overall, our study provides a framework for further analysis of the biological functions of AAT genes in either soybean or other crops.

Diversification and evolution of the SDG gene family in Brassica rapa after the whole genome triplication

Histone lysine methylation, controlled by the SET Domain Group (SDG) gene family, is part of the histone code that regulates chromatin function and epigenetic control of gene expression. Analyzing the SDG gene family in Brassica rapa for their gene structure, domain architecture, subcellular localization, rate of molecular evolution and gene expression pattern revealed common occurrences of subfunctionalization and neofunctionalization in BrSDGs. In comparison with Arabidopsis thaliana, the BrSDG gene family was found to be more divergent than AtSDGs, which might partly explain the rich variety of morphotypes in B. rapa. In addition, a new evolutionary pattern of the four main groups of SDGs was presented, in which the Trx group and the SUVR subgroup evolved faster than the E(z), Ash groups and the SUVH subgroup. These differences in evolutionary rate among the four main groups of SDGs are perhaps due to the complexity and variability of the regions that bind with biomacromolecules, which guide SDGs to their target loci.

Evolution of Prdm Genes in Animals: Insights from Comparative Genomics

Prdm genes encode transcription factors with a subtype of SET domain known as the PRDF1-RIZ (PR) homology domain and a variable number of zinc finger motifs. These genes are involved in a wide variety of functions during animal development. As most Prdm genes have been studied in vertebrates, especially in mice, little is known about the evolution of this gene family. We searched for Prdm genes in the fully sequenced genomes of 93 different species representative of all the main metazoan lineages. A total of 976 Prdm genes were identified in these species. The number of Prdm genes per species ranges from 2 to 19. To better understand how the Prdm gene family has evolved in metazoans, we performed phylogenetic analyses using this large set of identified Prdm genes. These analyses allowed us to define 14 different subfamilies of Prdm genes and to establish, through ancestral state reconstruction, that 11 of them are ancestral to bilaterian animals. Three additional subfamilies were acquired during early vertebrate evolution (Prdm5, Prdm11, and Prdm17). Several gene duplication and gene loss events were identified and mapped onto the metazoan phylogenetic tree. By studying a large number of nonmetazoan genomes, we confirmed that Prdm genes likely constitute a metazoan-specific gene family. Our data also suggest that Prdm genes originated before the diversification of animals through the association of a single ancestral SET domain encoding gene with one or several zinc finger encoding genes.

Evolutionary History of the Smyd Gene Family in Metazoans: A Framework to Identify the Orthologs of Human Smyd Genes in Drosophila and Other Animal Species

The Smyd gene family code for proteins containing a conserved core consisting of a SET domain interrupted by a MYND zinc finger. Smyd proteins are important in epigenetic control of development and carcinogenesis, through posttranslational modifications in histones and other proteins. Previous reports indicated that the Smyd family is quite variable in metazoans, so a rigorous phylogenetic reconstruction of this complex gene family is of central importance to understand its evolutionary history and functional diversification or conservation. We have performed a phylogenetic analysis of Smyd protein sequences, and our results show that the extant metazoan Smyd genes can be classified in three main classes, Smyd3 (which includes chordate-specific Smyd1 and Smyd2 genes), Smyd4 and Smyd5. In addition, there is an arthropod-specific class, SmydA. While the evolutionary history of the Smyd3 and Smyd5 classes is relatively simple, the Smyd4 class has suffered several events of gene loss, gene duplication and lineage-specific expansions in the animal phyla included in our analysis. A more specific study of the four Smyd4 genes in Drosophila melanogaster shows that they are not redundant, since their patterns of expression are different and knock-down of individual genes can have dramatic phenotypes despite the presence of the other family members.

Differential evolution of members of the rhomboid gene family with conservative and divergent patterns

Rhomboid proteins are intramembrane serine proteases that are involved in a plethora of biological functions, but the evolutionary history of the rhomboid gene family is not clear. We performed a comprehensive molecular evolutionary analysis of the rhomboid gene family and also investigated the organization and sequence features of plant rhomboids in different subfamilies. Our results showed that eukaryotic rhomboids could be divided into five subfamilies (RhoA-RhoD and PARL). Most orthology groups appeared to be conserved only as single or low-copy genes in all lineages in RhoB-RhoD and PARL, whereas RhoA genes underwent several duplication events, resulting in multiple gene copies. These duplication events were due to whole genome duplications in plants and animals and the duplicates might have experienced functional divergence. We also identified a novel group of plant rhomboid (RhoB1) that might have lost their enzymatic activity; their existence suggests that they might have evolved new mechanisms. Plant and animal rhomboids have similar evolutionary patterns. In addition, there are mutations affecting key active sites in RBL8, RBL9 and one of the Brassicaceae PARL duplicates. This study delineates a possible evolutionary scheme for intramembrane proteins and illustrates distinct fates and a mechanism of evolution of gene duplicates.

The molecular biology of meiosis in plants

Meiosis is the cell division that reshuffles genetic information between generations. Recently, much progress has been made in understanding this process; in particular, the identification and functional analysis of more than 80 plant genes involved in meiosis have dramatically deepened our knowledge of this peculiar cell division. In this review, we provide an overview of advancements in the understanding of all aspects of plant meiosis, including recombination, chromosome synapsis, cell cycle control, chromosome distribution, and the challenge of polyploidy.

Local effect of enhancer of zeste-like reveals cooperation of epigenetic and cis-acting determinants for zygotic genome rearrangements

In the ciliate Paramecium tetraurelia, differentiation of the somatic nucleus from the zygotic nucleus is characterized by massive and reproducible deletion of transposable elements and of 45,000 short, dispersed, single-copy sequences. A specific class of small RNAs produced by the germline during meiosis, the scnRNAs, are involved in the epigenetic regulation of DNA deletion but the underlying mechanisms are poorly understood. Here, we show that trimethylation of histone H3 (H3K27me3 and H3K9me3) displays a dynamic nuclear localization that is altered when the endonuclease required for DNA elimination is depleted. We identified the putative histone methyltransferase Ezl1 necessary for H3K27me3 and H3K9me3 establishment and show that it is required for correct genome rearrangements. Genome-wide analyses show that scnRNA-mediated H3 trimethylation is necessary for the elimination of long, repeated germline DNA, while single copy sequences display differential sensitivity to depletion of proteins involved in the scnRNA pathway, Ezl1- a putative histone methyltransferase and Dcl5- a protein required for iesRNA biogenesis. Our study reveals cis-acting determinants, such as DNA length, also contribute to the definition of germline sequences to delete. We further show that precise excision of single copy DNA elements, as short as 26 bp, requires Ezl1, suggesting that development specific H3K27me3 and H3K9me3 ensure specific demarcation of very short germline sequences from the adjacent somatic sequences.

The unicellular eukaryote Paramecium tetraurelia provides an extraordinary model for studying the mechanisms involved in zygotic genome rearrangements. At each sexual cycle, differentiation of the somatic nucleus from the zygotic nucleus is characterized by extensive remodeling of the entire somatic genome, which includes the precise excision of 45,000 short noncoding germline DNA segments to reconstitute functional open reading frames. Exploiting the unique properties of the Paramecium genome, we show that the enhancer of zeste like protein Ezl1 is necessary for histone H3 trimethylation on lysines 27 and 9 and is required for the precise excision of 31,000 of these single copy, dispersed germline DNA segments that can be as short as 26 bp in length. This implies that histone marks usually associated with heterochromatin may contribute to the precise demarcation of segments that are even shorter than the length of DNA wrapped around a single nucleosome. A quantitative analysis of high throughput sequencing datasets further shows that the underlying genetic properties of the germline DNA segments might act in concert with epigenetic signals to define germline specific sequences.

Uncovering the protein lysine and arginine methylation network in Arabidopsis chloroplasts

Post-translational modification of proteins by the addition of methyl groups to the side chains of Lys and Arg residues is proposed to play important roles in many cellular processes. In plants, identification of non-histone methylproteins at a cellular or subcellular scale is still missing. To gain insights into the extent of this modification in chloroplasts we used a bioinformatics approach to identify protein methyltransferases targeted to plastids and set up a workflow to specifically identify Lys and Arg methylated proteins from proteomic data used to produce the Arabidopsis chloroplast proteome. With this approach we could identify 31 high-confidence Lys and Arg methylation sites from 23 chloroplastic proteins, of which only two were previously known to be methylated. These methylproteins are split between the stroma, thylakoids and envelope sub-compartments. They belong to essential metabolic processes, including photosynthesis, and to the chloroplast biogenesis and maintenance machinery (translation, protein import, division). Also, the in silico identification of nine protein methyltransferases that are known or predicted to be targeted to plastids provided a foundation to build the enzymes/substrates relationships that govern methylation in chloroplasts. Thereby, using in vitro methylation assays with chloroplast stroma as a source of methyltransferases we confirmed the methylation sites of two targets, plastid ribosomal protein L11 and the β-subunit of ATP synthase. Furthermore, a biochemical screening of recombinant chloroplastic protein Lys methyltransferases allowed us to identify the enzymes involved in the modification of these substrates. The present study provides a useful resource to build the methyltransferases/methylproteins network and to elucidate the role of protein methylation in chloroplast biology.

Analysis of Arabidopsis floral transcriptome: detection of new florally expressed genes and expansion of Brassicaceae-specific gene families

The flower is essential for sexual reproduction of flowering plants and has been extensively studied. However, it is still not clear how many genes are expressed in the flower. Here, we performed RNA-seq analysis as a highly sensitive approach to investigate the Arabidopsis floral transcriptome at three developmental stages. We provide evidence that at least 23, 961 genes are active in the Arabidopsis flower, including 8512 genes that have not been reported as florally expressed previously. We compared gene expression at different stages and found that many genes encoding transcription factors are preferentially expressed in early flower development. Other genes with expression at distinct developmental stages included DUF577 in meiotic cells and DUF220, DUF1216, and Oleosin in stage 12 flowers. DUF1216 and DUF577 are Brassicaceae specific, and together with other families experienced expansion within the Brassicaceae lineage, suggesting novel/greater roles in Brassicaceae floral development than other plants. The large dataset from this study can serve as a resource for expression analysis of genes involved in flower development in Arabidopsis and for comparison with other species. Together, this work provides clues regarding molecular networks underlying flower development.

Horizontal gene transfer of epigenetic machinery and evolution of parasitism in the malaria parasite Plasmodium falciparum and other apicomplexans

Background

The acquisition of complex transcriptional regulatory abilities and epigenetic machinery facilitated the transition of the ancestor of apicomplexans from a free-living organism to an obligate parasite. The ability to control sophisticated gene expression patterns enabled these ancient organisms to evolve several differentiated forms, invade multiple hosts and evade host immunity. How these abilities were acquired remains an outstanding question in protistan biology.

Results

In this work, we study SET domain bearing genes that are implicated in mediating immune evasion, invasion and cytoadhesion pathways of modern apicomplexans, including malaria parasites. We provide the first conclusive evidence of a horizontal gene transfer of a Histone H4 Lysine 20 (H4K20) modifier, Set8, from an animal host to the ancestor of apicomplexans. Set8 is known to contribute to the coordinated expression of genes involved in immune evasion in modern apicomplexans. We also show the likely transfer of a H3K36 methyltransferase (Ashr3 from plants), possibly derived from algal endosymbionts. These transfers appear to date to the transition from free-living organisms to parasitism and coincide with the proposed horizontal acquisition of cytoadhesion domains, the O-glycosyltransferase that modifies these domains, and the primary family of transcription factors found in apicomplexan parasites. Notably, phylogenetic support for these conclusions is robust and the genes clearly are dissimilar to SET sequences found in the closely related parasite Perkinsus marinus, and in ciliates, the nearest free-living organisms with complete genome sequences available.

Conclusions

Animal and plant sources of epigenetic machinery provide new insights into the evolution of parasitism in apicomplexans. Along with the horizontal transfer of cytoadhesive domains, O-linked glycosylation and key transcription factors, the acquisition of SET domain methyltransferases marks a key transitional event in the evolution to parasitism in this important protozoan lineage.