The DNA dioxygenase ALKBH2 protects Arabidopsis thaliana against methylation damage

Discovery of a Potent and Cell-Active Inhibitor of DNA 6mA Demethylase ALKBH1

N6-Methyladenine (6mA) of DNA has emerged as a novel epigenetic mark in eukaryotes, and several 6mA effector proteins have been identified. However, efforts to selectively inhibit the biological functions of these effector proteins with small molecules are unsuccessful to date. Here we report the first potent and selective small molecule inhibitor (13h) of AlkB homologue 1 (ALKBH1), the only validated 6mA demethylase. 13h showed an IC50 of 0.026 ± 0.013 μM and 1.39 ± 0.13 μM in the fluorescence polarization (FP) and enzyme activity assay, respectively, and a KD of 0.112 ± 0.017 μM in the isothermal titration calorimetry (ITC) assay. The potency of 13h was well explained by the cocrystal structure of the 13h-ALKBH1 complex. Furthermore, 13h displayed excellent selectivity for ALKBH1. In cells, compound 13h and its derivative 16 were able to engage ALKBH1 and modulate the 6mA levels. Collectively, our study identified the first potent, isoform selective, and cell-active ALKBH1 inhibitor, providing a tool compound for exploring the biological functions of ALKBH1 and DNA 6mA.

Multiple Physiological and Biochemical Functions of Ascorbic Acid in Plant Growth, Development, and Abiotic Stress Response

Ascorbic acid (AsA) is an important nutrient for human health and disease cures, and it is also a crucial indicator for the quality of fruit and vegetables. As a reductant, AsA plays a pivotal role in maintaining the intracellular redox balance throughout all the stages of plant growth and development, fruit ripening, and abiotic stress responses. In recent years, the de novo synthesis and regulation at the transcriptional level and post-transcriptional level of AsA in plants have been studied relatively thoroughly. However, a comprehensive and systematic summary about AsA-involved biochemical pathways, as well as AsA's physiological functions in plants, is still lacking. In this review, we summarize and discuss the multiple physiological and biochemical functions of AsA in plants, including its involvement as a cofactor, substrate, antioxidant, and pro-oxidant. This review will help to facilitate a better understanding of the multiple functions of AsA in plant cells, as well as provide information on how to utilize AsA more efficiently by using modern molecular biology methods.

Phylogenetic and functional analyses of N6-methyladenosine RNA methylation factors in the wheat scab fungus Fusarium graminearum

In eukaryotes, N6-methyladenosine (m6A) RNA modification plays a crucial role in governing the fate of RNA molecules and has been linked to various developmental processes. However, the phyletic distribution and functions of genetic factors responsible for m6A modification remain largely unexplored in fungi. To get insights into the evolution of m6A machineries, we reconstructed global phylogenies of potential m6A writers, readers, and erasers in fungi. Substantial copy number variations were observed, ranging from up to five m6A writers in early-diverging fungi to a single copy in the subphylum Pezizomycotina, which primarily comprises filamentous fungi. To characterize m6A factors in a phytopathogenic fungus Fusarium graminearum, we generated knockout mutants lacking potential m6A factors including the sole m6A writer MTA1. However, the resulting knockouts did not exhibit any noticeable phenotypic changes during vegetative and sexual growth stages. As obtaining a homozygous knockout lacking MTA1 was likely hindered by its essential role, we generated MTA1-overexpressing strains (MTA1-OE). The MTA1-OE5 strain showed delayed conidial germination and reduced hyphal branching, suggesting its involvement during vegetative growth. Consistent with these findings, the expression levels of MTA1 and a potential m6A reader YTH1 were dramatically induced in germinating conidia, followed by the expression of potential m6A erasers at later vegetative stages. Several genes including transcription factors, transporters, and various enzymes were found to be significantly upregulated and downregulated in the MTA1-OE5 strain. Overall, our study highlights the functional importance of the m6A methylation during conidial germination in F. graminearum and provides a foundation for future investigations into m6A modification sites in filamentous fungi.IMPORTANCEN6-methyladenosine (m6A) RNA methylation is a reversible posttranscriptional modification that regulates RNA function and plays a crucial role in diverse developmental processes. This study addresses the knowledge gap regarding phyletic distribution and functions of m6A factors in fungi. The identification of copy number variations among fungal groups enriches our knowledge regarding the evolution of m6A machinery in fungi. Functional characterization of m6A factors in a phytopathogenic filamentous fungus Fusarium graminearum provides insights into the essential role of the m6A writer MTA1 in conidial germination and hyphal branching. The observed effects of overexpressing MTA1 on fungal growth and gene expression patterns of m6A factors throughout the life cycle of F. graminearum further underscore the importance of m6A modification in conidial germination. Overall, this study significantly advances our understanding of m6A modification in fungi, paving the way for future research into its roles in filamentous growth and potential applications in disease control.

Knockout of SlALKBH2 weakens the DNA damage repair ability of tomato

During the growth and evolution of plants, genomic DNA is subject to constant assault from endogenous and environmental DNA damage compounds, which will result in mutagenic or genotoxic covalent adducts. Whether for prokaryotes, eukaryotes or even viruses, maintaining genome integrity is critical for the continuation of life. Escherichia coli and mammals have evolved the AlkB family of Fe(II)/alpha-ketoglutarate-dependent dioxygenases that repair DNA alkylation damage. We identified a functional homologue with EsAlkB and HsALKBH2 in tomatoes, and named it SlALKBH2. In our study, the SlALKBH2 knockout mutant showed hypersensitivity to the DNA mutagen MMS and displayed more severe growth abnormalities than wild-type plants under mutagen treatment, such as slow growth, leaf deformation and early senescence. Additionally, genes with high transcriptional activity, such as rDNA, have increased methylation under MMS treatment. In conclusion, this study shows that the tomato SlALKBH2 gene may play an important role in ensuring the integrity of the genome.

Genome-wide sequence identification and expression analysis of N6 -methyladenosine demethylase in sugar beet (Beta vulgaris L.) under salt stress

In eukaryotes, N⁶ -methyladenosine (m⁶A) is the most abundant and highly conserved RNA modification. In vivo, m⁶A demethylase dynamically regulates the m⁶A level by removing the m⁶A marker where it plays an important role in plant growth, development and response to abiotic stress. The confirmed m⁶A demethylases in Arabidopsis thaliana include ALKBH9B and ALKBH10B, both belonging to the ALKB family. In this study, BvALKB family members were identified in sugar beet genome-wide database, and their conserved domains, gene structures, chromosomal locations, phylogeny, conserved motifs and expression of BvALKB genes were analyzed. Almost all BvALKB proteins contained the conserved domain of 2OG-Fe II-Oxy. Phylogenetic analysis suggested that the ten proteins were clustered into five groups, each of which had similar motifs and gene structures. Three Arabidopsis m⁶A demethylase-homologous proteins (BvALKBH6B, BvALKBH8B and BvALKBH10B) were of particular interest in our study. Expression profile analysis showed that almost all genes were up-regulated or down-regulated to varying degrees under salt stress. More specifically, BvALKBH10B homologous to AtALKBH10B was significantly up-regulated, suggesting that the transcriptional activity of this gene is responsive to salt stress. This study provides a theoretical basis for further screening of m⁶A demethylase in sugar beet, and also lays a foundation for studying the role of ALKB family proteins in growth, development and response to salinity stress.

Roles of the 2-Oxoglutarate-Dependent Dioxygenase Superfamily in the Flavonoid Pathway: A Review of the Functional Diversity of F3H, FNS I, FLS, and LDOX/ANS

The 2-oxoglutarate-dependent dioxygenase (2-OGD) superfamily is one of the largest protein families in plants. The main oxidation reactions they catalyze in plants are hydroxylation, desaturation, demethylation, epimerization, and halogenation. Four members of the 2-OGD superfamily, i.e., flavonone 3β-hydroxylase (F3H), flavones synthase I (FNS I), flavonol synthase (FLS), and anthocyanidin synthase (ANS)/leucoanthocyanidin dioxygenase (LDOX), are present in the flavonoid pathway, catalyzing hydroxylation and desaturation reactions. In this review, we summarize the recent research progress on these proteins, from the discovery of their enzymatic activity, to their functional verification, to the analysis of the response they mediate in plants towards adversity. Substrate diversity analysis indicated that F3H, FNS Ⅰ, ANS/LDOX, and FLS perform their respective dominant functions in the flavonoid pathway, despite the presence of functional redundancy among them. The phylogenetic tree classified two types of FNS Ⅰ, one mainly performing FNS activity, and the other, a new type of FNS present in angiosperms, mainly involved in C-5 hydroxylation of SA. Additionally, a new class of LDOXs is highlighted, which can catalyze the conversion of (+)-catechin to cyanidin, further influencing the starter and extension unit composition of proanthocyanidins (PAs). The systematical description of the functional diversity and evolutionary relationship among these enzymes can facilitate the understanding of their impacts on plant metabolism. On the other hand, it provides molecular genetic evidence of the chemical evolution of flavonoids from lower to higher plants, promoting plant adaptation to harsh environments.

DNA Methylation on N6-Adenine Regulates the Hyphal Development during Dimorphism in the Early-Diverging Fungus Mucor lusitanicus

The epigenetic modifications control the pathogenicity of human pathogenic fungi, which have been poorly studied in Mucorales, causative agents of mucormycosis. This order belongs to a group referred to as early-diverging fungi that are characterized by high levels of N6-methyldeoxy adenine (6mA) in their genome with dense 6mA clusters associated with actively expressed genes. AlkB enzymes can act as demethylases of 6mA in DNA, with the most remarkable eukaryotic examples being mammalian ALKBH1 and Caenorhabditis elegans NMAD-1. The Mucor lusitanicus (formerly M. circinelloides f. lusitanicus) genome contains one gene, dmt1, and two genes, dmt2 and dmt3, encoding proteins similar to C. elegans NMAD-1 and ALKBH1, respectively. The function of these three genes was analyzed by the generation of single and double deletion mutants for each gene. Multiple processes were studied in the mutants, but defects were only found in single and double deletion mutants for dmt1. In contrast to the wild-type strain, dmt1 mutants showed an increase in 6mA levels during the dimorphic transition, suggesting that 6mA is associated with dimorphism in M. lusitanicus. Furthermore, the spores of dmt1 mutants challenged with macrophages underwent a reduction in polar growth, suggesting that 6mA also has a role during the spore–macrophage interaction that could be important in the infection process.

Mechanisms of Genome Maintenance in Plants: Playing It Safe With Breaks and Bumps

Maintenance of genomic integrity is critical for the perpetuation of all forms of life including humans. Living organisms are constantly exposed to stress from internal metabolic processes and external environmental sources causing damage to the DNA, thereby promoting genomic instability. To counter the deleterious effects of genomic instability, organisms have evolved general and specific DNA damage repair (DDR) pathways that act either independently or mutually to repair the DNA damage. The mechanisms by which various DNA repair pathways are activated have been fairly investigated in model organisms including bacteria, fungi, and mammals; however, very little is known regarding how plants sense and repair DNA damage. Plants being sessile are innately exposed to a wide range of DNA-damaging agents both from biotic and abiotic sources such as ultraviolet rays or metabolic by-products. To escape their harmful effects, plants also harbor highly conserved DDR pathways that share several components with the DDR machinery of other organisms. Maintenance of genomic integrity is key for plant survival due to lack of reserve germline as the derivation of the new plant occurs from the meristem. Untowardly, the accumulation of mutations in the meristem will result in a wide range of genetic abnormalities in new plants affecting plant growth development and crop yield. In this review, we will discuss various DNA repair pathways in plants and describe how the deficiency of each repair pathway affects plant growth and development.

Structural determinants of nucleobase modification recognition in the AlkB family of dioxygenases

Iron-dependent dioxygenases of the AlkB protein family found in most organisms throughout the tree of life play a major role in oxidative dealkylation processes. Many of these enzymes have attracted the attention of researchers across different fields and have been subjected to thorough biochemical characterization because of their link to human health and disease. For example, several mammalian AlkB homologues are involved in the direct reversal of alkylation damage in DNA, while others have been shown to play a regulatory role in epigenetic or epitranscriptomic nucleic acid methylation or in post-translational modifications such as acetylation of actin filaments. These studies show that that divergence in amino acid sequence and structure leads to different characteristics and substrate specificities. In this review, we aim to summarize current insights in the structural features involved in the substrate selection of AlkB homologues, with focus on nucleic acid interactions.

Human and Arabidopsis alpha-ketoglutarate-dependent dioxygenase homolog proteins-New players in important regulatory processes

The family of AlkB homolog (ALKBH) proteins, the homologs of Escherichia coli AlkB 2-oxoglutarate (2OG), and Fe(II)-dependent dioxygenase are involved in a number of important regulatory processes in eukaryotic cells including repair of alkylation lesions in DNA, RNA, and nucleoprotein complexes. There are nine human and thirteen Arabidopsis thaliana ALKBH proteins described, which exhibit diversified functions. Among them, human ALKBH5 and FaT mass and Obesity-associated (FTO) protein and Arabidopsis ALKBH9B and ALKBH10B have been recognized as N⁶ methyladenine (N⁶ meA) demethylases, the most abundant posttranscriptional modification in mRNA. The FTO protein is reported to be associated with obesity and type 2 diabetes, and involved in multiple other processes, while ALKBH5 is induced by hypoxia. Arabidopsis ALKBH9B is an N⁶ meA demethylase influencing plant susceptibility to viral infections via m⁶ A/A ratio control in viral RNA. ALKBH10B has been discovered to be a functional Arabidopsis homolog of FTO; thus, it is also an RNA N⁶ meA demethylase involved in plant flowering and several other regulatory processes including control of metabolism. High-throughput mass spectrometry showed multiple sites of human ALKBH phosphorylation. In the case of FTO, the type of modified residue decides about the further processing of the protein. This modification may result in subsequent protein ubiquitination and proteolysis, or in the blocking of these processes. However, the impact of phosphorylation on the other ALKBH function and their downstream pathways remains nearly unexplored in both human and Arabidopsis. Therefore, the investigation of evolutionarily conserved functions of ALKBH proteins and their regulatory impact on important cellular processes is clearly called for.

Expanding the roles for 2-oxoglutarate-dependent oxygenases in plant metabolism

Covering: up to 2018 2-Oxoglutarate-dependent oxygenases (2ODOs) comprise a large enzyme superfamily in plant genomes, second in size only to the cytochromes P450 monooxygenase (CYP) superfamily. 2ODOs participate in both primary and specialized plant pathways, and their occurrence across all life kingdoms points to an ancient origin. Phylogenetic evidence supports substantial expansion and diversification of 2ODOs following the split from the common ancestor of land plants. More conserved roles for these enzymes include oxidation within hormone metabolism, such as the recently described capacity of Dioxygenase for Auxin Oxidation (DAO) for governing auxin homeostasis. Conserved structural features among 2ODOs has provided a basis for continued investigation into their mechanisms, and recent structural work is expected to illuminate intriguing reactions such as that of 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO). Phylogenetic radiation among this superfamily combined with neo- and subfunctionalization has enabled recruitment to highly specialized pathways, including those yielding medicines, flavours, dyes, poisons, and compounds important for plant-environment interactions. Catalytic versatility of 2ODOs in plants and across broader taxa continues to inspire biochemists tasked with the discovery of new enzymes. This highlight article summarizes recent reports up to 2018 of 2ODOs within plant metabolism. Furthermore, the respective contributions of 2ODOs and other oxidases to natural product biosynthesis are discussed as a framework for continued discovery.

Prediction of regulatory long intergenic non-coding RNAs acting in trans through base-pairing interactions

Background

Long intergenic non-coding RNAs (lincRNAs) can act as regulators of expression of protein-coding genes. Trans-natural antisense transcripts (trans-NATs) are a type of lincRNAs that contain sequence complementary to mRNA from other loci. The regulatory potential of trans-NATs has been poorly studied in eukaryotes and no example of trans-NATs regulating gene expression in plants are reported. The goal of this study was to identify lincRNAs, and particularly trans-NATs, in Arabidopsis thaliana that have a potential to regulate expression of target genes in trans at the transcriptional or translational level.

Results

We identified 1001 lincRNAs using an RNAseq dataset from total polyA⁺ and polysome-associated RNA of seedlings grown under high and low phosphate, or shoots and roots treated with different phytohormones, of which 550 were differentially regulated. Approximately 30% of lincRNAs showed conservation amongst Brassicaceae and 25% harbored transposon element (TE) sequences. Gene co-expression network analysis highlighted a group of lincRNAs associated with the response of roots to low phosphate. A total of 129 trans-NATs were predicted, of which 88 were significantly differentially expressed under at least one pairwise comparison. Five trans-NATs showed a positive correlation between their expression and target mRNA steady-state levels, and three showed a negative correlation. Expression of four trans-NATs positively correlated with a change in target mRNA polysome association. The regulatory potential of these trans-NATs did not implicate miRNA mimics nor siRNAs. We also looked for lincRNAs that could regulate gene expression in trans by Watson-Crick DNA:RNA base pairing with target protein-encoding loci. We identified 100 and 81 with a positive or negative correlation, respectively, with steady-state level of their predicted target. The regulatory potential of one such candidate lincRNA harboring a SINE TE sequence was validated in a protoplast assay on three distinct genes containing homologous TE sequence in their promoters. Construction of networks highlighted other putative lincRNAs with multiple predicted target loci for which expression was positively correlated with target gene expression.

Conclusions

This study identified lincRNAs in Arabidopsis with potential in regulating target gene expression in trans by both RNA:RNA and RNA:DNA base pairing and highlights lincRNAs harboring TE sequences in such activity.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5946-0) contains supplementary material, which is available to authorized users.

Metabolic and gene expression hallmarks of seed germination uncovered by sodium butyrate in Medicago truncatula

Because high-quality seeds are essential for successful crop production in challenging environments, understanding the molecular bases of seed vigour will lead to advances in seed technology. Histone deacetylase inhibitors, promoting histone hyperacetylation, are used as tools to explore aspects still uncovered of the abiotic stress response in plants. The aim of this work was to investigate novel signatures of seed germination in Medicago truncatula, using the histone deacetylase inhibitor sodium butyrate (NaB) as stress agent. NaB-treated and untreated seeds collected at 2 and 8 hr of imbibition and at the radicle protrusion stage underwent molecular phenotyping and nontargeted metabolome profiling. Quantitative enrichment analysis revealed the influence of NaB on seed nucleotide, amino acid, lipid, and carbohydrate metabolism. Up-regulation of antioxidant and polyamine biosynthesis genes occurred in response to NaB. DNA damage evidenced in NaB-treated seeds correlated with up-regulation of base-excision repair genes. Changes in N¹ -methyladenosine and N¹ -methylguanine were associated with up-regulation of MtALKBH1 (alkylation repair homolog) gene. N² ,N² -dimethylguanosine and 5-methylcytidine, tRNA modifications involved in the post-transcriptional regulation of DNA damage response, were also accumulated in NaB-treated seeds at the radicle protrusion stage. The observed changes in seed metabolism can provide novel potential metabolic hallmarks of germination.

The Origin and Evolution of Plant Flavonoid Metabolism

During their evolution, plants have acquired the ability to produce a huge variety of compounds. Unlike the specialized metabolites that accumulate in limited numbers of species, flavonoids are widely distributed in the plant kingdom. Therefore, a detailed analysis of flavonoid metabolism in genomics and metabolomics is an ideal way to investigate how plants have developed their unique metabolic pathways during the process of evolution. More comprehensive and precise metabolite profiling integrated with genomic information are helpful to emerge unexpected gene functions and/or pathways. The distribution of flavonoids and their biosynthetic genes in the plant kingdom suggests that flavonoid biosynthetic pathways evolved through a series of steps. The enzymes that form the flavonoid scaffold structures probably first appeared by recruitment of enzymes from primary metabolic pathways, and later, enzymes that belong to superfamilies such as 2-oxoglutarate-dependent dioxygenase, cytochrome P450, and short-chain dehydrogenase/reductase modified and varied the structures. It is widely accepted that the first two enzymes in flavonoid biosynthesis, chalcone synthase, and chalcone isomerase, were derived from common ancestors with enzymes in lipid metabolism. Later enzymes acquired their function by gene duplication and the subsequent acquisition of new functions. In this review, we describe the recent progress in metabolomics technologies for flavonoids and the evolution of flavonoid skeleton biosynthetic enzymes to understand the complicate evolutionary traits of flavonoid metabolism in plant kingdom.

INCURVATA11 and CUPULIFORMIS2 Are Redundant Genes That Encode Epigenetic Machinery Components in Arabidopsis

All critical developmental and physiological events in a plant's life cycle depend on the proper activation and repression of specific gene sets, and this often involves epigenetic mechanisms. Some Arabidopsis thaliana mutants with disorders of the epigenetic machinery exhibit pleiotropic defects, including incurved leaves and early flowering, due to the ectopic and heterochronic derepression of developmental regulators. Here, we studied one such mutant class, the incurvata11 (icu11) loss-of-function mutants. We have identified ICU11 as the founding member of a small gene family that we have named CUPULIFORMIS (CP). This family is part of the 2-oxoglutarate/Fe(II)-dependent dioxygenase superfamily. ICU11 and its closest paralog, CP2, have unequally redundant functions: although cp2 mutants are phenotypically wild type, icu11 cp2 double mutants skip vegetative development and flower upon germination. This phenotype is reminiscent of loss-of-function mutants of the Polycomb-group genes EMBRYONIC FLOWER1 (EMF1) and EMF2 Double mutants harboring icu11 alleles and loss-of-function alleles of genes encoding components of the epigenetic machinery exhibit synergistic, severe phenotypes, and some are similar to those of emf mutants. Hundreds of genes are misexpressed in icu11 plants, including SEPALLATA3 (SEP3), and derepression of SEP3 causes the leaf phenotype of icu11 ICU11 and CP2 are nucleoplasmic proteins that act as epigenetic repressors through an unknown mechanism involving histone modification, but not DNA methylation.

ALKBH7 drives a tissue and sex-specific necrotic cell death response following alkylation-induced damage

Regulated necrosis has emerged as a major cell death mechanism in response to different forms of physiological and pharmacological stress. The AlkB homolog 7 (ALKBH7) protein is required for regulated cellular necrosis in response to chemotherapeutic alkylating agents but its role within a whole organism is unknown. Here, we show that ALKBH7 modulates alkylation-induced cellular death through a tissue and sex-specific mechanism. At the whole-animal level, we find that ALKBH7 deficiency confers increased resistance to MMS-induced toxicity in male but not female mice. Moreover, ALKBH7-deficient mice exhibit protection against alkylation-mediated cytotoxicity in retinal photoreceptor and cerebellar granule cells, two cell types that undergo necrotic death through the initiation of the base excision repair pathway and hyperactivation of the PARP1/ARTD1 enzyme. Notably, the protection against alkylation-induced cerebellar degeneration is specific to ALKBH7-deficient male but not female mice. Our results uncover an in vivo role for ALKBH7 in mediating a sexually dimorphic tissue response to alkylation damage that could influence individual responses to chemotherapies based upon alkylating agents.

The interaction between ALKBH2 DNA repair enzyme and PCNA is direct, mediated by the hydrophobic pocket of PCNA and perturbed in naturally-occurring ALKBH2 variants

Human AlkB homolog 2 (ALKBH2) is a DNA repair enzyme that catalyzes the direct reversal of DNA methylation damage through oxidative demethylation. While ALKBH2 colocalizes with proliferating cell nuclear antigen (PCNA) in DNA replication foci, it remains unknown whether these two proteins alone form a complex or require additional components for interaction. Here, we demonstrate that ALKBH2 can directly interact with PCNA independent from other cellular factors, and we identify the hydrophobic pocket of PCNA as the key domain mediating this interaction. Moreover, we find that PCNA association with ALKBH2 increases significantly during DNA replication, suggesting that ALKBH2 forms a cell-cycle dependent complex with PCNA. Intriguingly, we show that an ALKBH2 germline variant, as well as a variant found in cancer, display altered interaction with PCNA. Our studies reveal the ALKBH2 binding interface of PCNA and indicate that both germline and somatic ALKBH2 variants could have cellular effects on ALKBH2 function in DNA repair.

AlkB and Its Homologues – DNA Repair and Beyond

AlkB is an Fe(ii)/2-oxoglutarate-dependent dioxygenase that is part of the adaptive response to alkylating agents in Escherichia coli. AlkB hydroxylates a wide variety of alkylated DNA bases producing unstable intermediates which decompose to restore the non-alkylated bases. Homologues exist in other bacteria, metazoa (e.g. nine in humans), plants and viruses, but not in archaea, with many catalysing the same oxidative demethylation reactions as for AlkB. The mammalian enzymes Alkbh2 and Alkbh3 catalyse direct DNA repair, Alkbh5 and FTO (Alkbh9) are RNA demethylases, and Alkbh8 is used to synthesize a tRNA, while the remaining mammalian homologues have alternative functions. Alkbh1 is an apurinic/apyrimidinic lyase in addition to exhibiting demethylase activities, but no clear role for the Alkbh1 protein has emerged. Alkbh4 is involved in cell division and potentially demethylates actin, whereas the mitochondrial homologue Alkbh7 has a role in obesity; however, no enzymatic activity has been linked to Alkbh4 or Alkbh7. Here, we discuss AlkB as the ‘archetype’ of this class of hydroxylases, compare it to Alkbh2 and Alkbh3, and then briefly review the diverse (and largely unknown) functions of Alkbh1, Alkbh4, Alkbh6 and Alkbh7. Alkbh5, Alkbh8 and Alkbh9 (FTO) are described separately.

Involvement of Iron-Containing Proteins in Genome Integrity in Arabidopsis Thaliana

The Arabidopsis genome encodes numerous iron-containing proteins such as iron-sulfur (Fe-S) cluster proteins and hemoproteins. These proteins generally utilize iron as a cofactor, and they perform critical roles in photosynthesis, genome stability, electron transfer, and oxidation-reduction reactions. Plants have evolved sophisticated mechanisms to maintain iron homeostasis for the assembly of functional iron-containing proteins, thereby ensuring genome stability, cell development, and plant growth. Over the past few years, our understanding of iron-containing proteins and their functions involved in genome stability has expanded enormously. In this review, I provide the current perspectives on iron homeostasis in Arabidopsis, followed by a summary of iron-containing protein functions involved in genome stability maintenance and a discussion of their possible molecular mechanisms.

Functional diversity of 2-oxoglutarate/Fe(II)-dependent dioxygenases in plant metabolism

Oxidative enzymes catalyze many different reactions in plant metabolism. Among this suite of enzymes are the 2-oxoglutarate/Fe(II)-dependent dioxygenases (2-ODDs). Cytochromes P450 (CYPs) as often considered the most versatile oxidative enzymes in nature, but the diversity and complexity of reactions catalyzed by 2-ODDs is superior to the CYPs. The list of oxidative reactions catalyzed by 2-ODDs includes hydroxylations, demethylations, desaturations, ring closure, ring cleavage, epimerization, rearrangement, halogenation, and demethylenation. Furthermore, recent work, including the discovery of 2-ODDs involved in epigenetic regulation, and others catalyzing several characteristic steps in specialized metabolic pathways, support the argument that 2-ODDs are among the most versatile and important oxidizing biological catalysts. In this review, we survey and summarize the pertinent literature with a focus on several key reactions catalyzed by 2-ODDs, and discuss the significance and impact of these enzymes in plant metabolism.

Evolution and diversity of the 2-oxoglutarate-dependent dioxygenase superfamily in plants

The 2-oxoglutarate-dependent dioxygenase (2OGD) superfamily is the second largest enzyme family in the plant genome, and its members are involved in various oxygenation/hydroxylation reactions. Despite their biochemical significance in metabolism, a systematic analysis of plant 2OGDs remains to be accomplished. We present a phylogenetic classification of 479 2OGDs in six plant models, ranging from green algae to angiosperms. These were classified into three classes - DOXA, DOXB and DOXC - based on amino acid sequence similarity. The DOXA class includes plant homologs of Escherichia coli AlkB, which is a prototype of 2OGD involved in the oxidative demethylation of alkylated nucleic acids and histones. The DOXB class is conserved across all plant taxa and is involved in proline 4-hydroxylation in cell wall protein synthesis. The DOXC class is involved in specialized metabolism of various phytochemicals, including phytohormones and flavonoids. The vast majority of 2OGDs from land plants were classified into the DOXC class, but only seven from Chlamydomonas, suggesting that this class has diversified during land plant evolution. Phylogenetic analysis assigned DOXC-class 2OGDs to 57 phylogenetic clades. 2OGD genes involved in gibberellin biosynthesis were conserved among vascular plants, and those involved in flavonoid and ethylene biosynthesis were shared among seed plants. Several angiosperm-specific clades were found to be involved in various lineage-specific specialized metabolisms, but 31 of the 57 DOXC-class clades were only found in a single species. Therefore, the evolution and diversification of DOXC-class 2OGDs is partly responsible for the diversity and complexity of specialized metabolites in land plants.

DNA repair by reversal of DNA damage

Endogenous and exogenous factors constantly challenge cellular DNA, generating cytotoxic and/or mutagenic DNA adducts. As a result, organisms have evolved different mechanisms to defend against the deleterious effects of DNA damage. Among these diverse repair pathways, direct DNA-repair systems provide cells with simple yet efficient solutions to reverse covalent DNA adducts. In this review, we focus on recent advances in the field of direct DNA repair, namely, photolyase-, alkyltransferase-, and dioxygenase-mediated repair processes. We present specific examples to describe new findings of known enzymes and appealing discoveries of new proteins. At the end of this article, we also briefly discuss the influence of direct DNA repair on other fields of biology and its implication on the discovery of new biology.