Cloning and characterization of rice HMGB1 gene

Genome-Wide Identification and Expression Analysis of the High-Mobility Group B (HMGB) Gene Family in Plant Response to Abiotic Stress in Tomato

High-mobility group B (HMGB) proteins are a class of non-histone proteins associated with eukaryotic chromatin and are known to regulate a variety of biological processes in plants. However, the functions of HMGB genes in tomato (Solanum lycopersicum) remain largely unexplored. Here, we identified 11 members of the HMGB family in tomato using BLAST. We employed genome-wide identification, gene structure analysis, domain conservation analysis, cis-acting element analysis, collinearity analysis, and qRT-PCR-based expression analysis to study these 11 genes. These genes were categorized into four groups based on their unique protein domain structures. Despite their structural diversity, all members contain the HMG-box domain, a characteristic feature of the HMG superfamily. Syntenic analysis suggested that tomato SlHMGBs have close evolutionary relationships with their homologs in other dicots. The promoter regions of SlHMGBs are enriched with numerous cis-elements related to plant growth and development, phytohormone responsiveness, and stress responsiveness. Furthermore, SlHMGB members exhibited distinct tissue-specific expression profiles, suggesting their potential roles in regulating various aspects of plant growth and development. Most SlHMGB genes respond to a variety of abiotic stresses, including salt, drought, heat, and cold. For instance, SlHMGB2 and SlHMGB4 showed positive responses to salt, drought, and cold stresses. SlHMGB1, SlHMGB3, and SlHMGB8 were involved in responses to two types of stress: SlHMGB1 responded to drought and heat, while SlHMGB3 and SlHMGB8 responded to salt and heat. SlHMGB6 and SlHMGB11 were solely regulated by drought and heat stress, respectively. Under various treatment conditions, the number of up-regulated genes significantly outnumbered the down-regulated genes, implying that the SlHMGB family may play a crucial role in mitigating abiotic stress in tomato. These findings lay a foundation for further dissecting the precise roles of SlHMGB genes.

HMGB1 and Toll-like receptors: potential therapeutic targets in autoimmune diseases

HMGB1, a nucleoprotein, is expressed in almost all eukaryotic cells. During cell activation and cell death, HMGB1 can function as an alarm protein (alarmin) or damage-associated molecular pattern (DAMP) and mediate early inflammatory and immune response when it is translocated to the extracellular space. The binding of extracellular HMGB1 to Toll-like receptors (TLRs), such as TLR2 and TLR4 transforms HMGB1 into a pro-inflammatory cytokine, contributing to the occurrence and development of autoimmune diseases. TLRs, which are members of a family of pattern recognition receptors, can bind to endogenous DAMPs and activate the innate immune response. Additionally, TLRs are key signaling molecules mediating the immune response and play a critical role in the host defense against pathogens and the maintenance of immune balance. HMGB1 and TLRs are reported to be upregulated in several autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes mellitus, and autoimmune thyroid disease. The expression levels of HMGB1 and some TLRs are upregulated in tissues of patients with autoimmune diseases and animal models of autoimmune diseases. The suppression of HMGB1 and TLRs inhibits the progression of inflammation in animal models. Thus, HMGB1 and TLRs are indispensable biomarkers and important therapeutic targets for autoimmune diseases. This review provides comprehensive strategies for treating or preventing autoimmune diseases discovered in recent years.

Deciphering the Molecular Mechanisms of Chilling Tolerance in Lsi1-Overexpressing Rice

Improving tolerance to low-temperature stress during the rice seedling stage is of great significance in agricultural science. In this study, using the low silicon gene 1 (Lsi1)-overexpressing (Dular-OE) and wild-type rice (Dular-WT), we showed that Lsi1 overexpression enhances chilling tolerance in Dular-OE. The overexpression of the Lsi1 increases silicon absorption, but it was not the main reason for chilling tolerance in Dular-OE. Instead, our data suggest that the overexpression of a Lsi1-encoding NIP and its interaction with key proteins lead to chilling tolerance in Dular-OE. Additionally, we show that the high-mobility group protein (HMG1) binds to the promoter of Lsi1, positively regulating its expression. Moreover, Nod26-like major intrinsic protein (NIP)’s interaction with α and β subunits of ATP synthase and the 14-3-3f protein was validated by co-immunoprecipitation (Co-IP), bimolecular fluorescent complementary (BiFC), and GST-pulldown assays. Western blotting revealed that the overexpression of NIP positively regulates the ATP-synthase subunits that subsequently upregulate calcineurin B-like interacting protein kinases (CIPK) negatively regulating 14-3-3f. Overall, these NIP-mediated changes trigger corresponding pathways in an orderly manner, enhancing chilling tolerance in Dular-OE.

Systems-based rice improvement approaches for sustainable food and nutritional security

An integrated research approach to ensure sustainable rice yield increase of a crop grown by 25% of the world's farmers in 10% of cropland is essential for global food security. Rice, being a global staple crop, feeds about 56% of the world population and sustains 40% of the world's poor. At ~ $200 billion, it also accounts for 13% of the annual crop value. With hunger and malnutrition rampant among the poor, rice research for development is unique in global food and nutrition security. A systems-based, sustainable increase in rice quantity and quality is imperative for environmental and biodiversity benefits. Upstream 'discovery' through biotechnology, midstream 'development' through breeding and agronomy, downstream 'dissemination and deployment' must be 'demand-driven' for 'distinct socio-economic transformational impacts'. Local agro-ecology and livelihood nexus must drive the research agenda for targeted benefits. This necessitates sustained long-term investments by government, non-government and private sectors to secure the future food, nutrition, environment, prosperity and equity status.

Naturally Occurring HMGB1 Inhibitor, Glycyrrhizin, Modulates Chronic Seizures-Induced Memory Dysfunction in Zebrafish Model

Glycyrrhizin (GL) is a well-known pharmacological inhibitor of high mobility group box 1 (HMGB1) and is abundantly present in the licorice root (Glycyrrhiza radix). HMGB1 protein, a key mediator of neuroinflammation, has been implicated in several neurological disorders, including epilepsy. Epilepsy is a devastating neurological disorder with no effective disease-modifying treatment strategies yet, suggesting a pressing need for exploring novel therapeutic options. In the current investigation, using a second hit pentylenetetrazol (PTZ) induced chronic seizure model in adult zebrafish, regulated mRNA expression of HMGB1 was inhibited by pretreatment with GL (25, 50, and 100 mg/kg, ip). A molecular docking study suggests that GL establishes different binding interactions with the various amino acid chains of HMGB1 and Toll-like receptor-4 (TLR4). Our finding suggests that GL pretreatment reduces/suppresses second hit PTZ induced seizure, as shown by the reduction in the seizure score. GL also regulates the second hit PTZ induced behavioral impairment and rescued second hit PTZ related memory impairment as demonstrated by an increase in the inflection ratio (IR) at the 3 h and 24 h T-maze trial. GL inhibited seizure-induced neuronal activity as demonstrated by reduced C-fos mRNA expression. GL also modulated mRNA expression of BDNF, CREB-1, and NPY. The possible mechanism underlying the anticonvulsive effect of GL could be attributed to its anti-inflammatory activity, as demonstrated by the downregulated mRNA expression level of HMGB1, TLR4, NF-kB, and TNF-α. Overall, our finding suggests that GL exerts an anticonvulsive effect and ameliorates seizure-related memory disruption plausibly through regulating of the HMGB1-TLR4-NF-kB axis.

The Role of HMGB1, a Nuclear Damage-Associated Molecular Pattern Molecule, in the Pathogenesis of Lung Diseases

Significance: High-mobility group protein box 1 (HMGB1), a ubiquitous nuclear protein, regulates chromatin structure and modulates the expression of many genes involved in the pathogenesis of lung cancer and many other lung diseases, including those that regulate cell cycle control, cell death, and DNA replication and repair. Extracellular HMGB1, whether passively released or actively secreted, is a danger signal that elicits proinflammatory responses, impairs macrophage phagocytosis and efferocytosis, and alters vascular remodeling. This can result in excessive pulmonary inflammation and compromised host defense against lung infections, causing a deleterious feedback cycle. Recent Advances: HMGB1 has been identified as a biomarker and mediator of the pathogenesis of numerous lung disorders. In addition, post-translational modifications of HMGB1, including acetylation, phosphorylation, and oxidation, have been postulated to affect its localization and physiological and pathophysiological effects, such as the initiation and progression of lung diseases. Critical Issues: The molecular mechanisms underlying how HMGB1 drives the pathogenesis of different lung diseases and novel therapeutic approaches targeting HMGB1 remain to be elucidated. Future Directions: Additional research is needed to identify the roles and functions of modified HMGB1 produced by different post-translational modifications and their significance in the pathogenesis of lung diseases. Such studies will provide information for novel approaches targeting HMGB1 as a treatment for lung diseases.

C-terminal extension of calmodulin-like 3 protein from Oryza sativa L.: interaction with a high mobility group target protein

A large number of calmodulin-like (CML) proteins are present in plants, but there is little detailed information on the functions of these proteins in rice (Oryza sativa L.). Here, the CML3 protein from rice (OsCML3) and its truncated form lacking the C-terminal extension (OsCML3m) were found to exhibit a Ca2+-binding property and subsequent conformational change, but the ability to bind the CaM kinase II peptide was only observed for OsCML3m. Changes in their secondary structure upon Ca2+-binding measured by circular dichroism revealed that OsCML3m had a higher helical content than OsCML3. Moreover, OsCML3 was mainly localized in the plasma membrane, whereas OsCML3m was found in the nucleus. The rice high mobility group B1 (OsHMGB1) protein was identified as one of the putative OsCML3 target proteins. Bimolecular fluorescence complementation analysis revealed that OsHMGB1 bound OsCML3, OsCML3m or OsCML3s (cysteine to serine mutation at the prenylation site) in the nucleus presumably through the methionine and phenylalanine-rich hydrophobic patches, confirming that OsHMGB1 is a target protein in planta. The effect of OsCML3 or OsCML3m on the DNA-binding ability of OsHMGB1 was measured using an electrophoretic mobility shift assay. OsCML3m decreased the level of OsHMGB1 binding to pUC19 double-stranded DNA whereas OsCML3 did not. Taken together, OsCML3 probably provides a mechanism for manipulating the DNA-binding ability of OsHMGB1 in the nucleus and its C-terminal extension provides an intracellular Ca2+ regulatory switch.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Peroxisome proliferator-activated receptor γ agonist troglitazone inhibits high mobility group box 1 expression in endothelial cells via suppressing transcriptional activity of nuclear factor κB and activator protein 1

High mobility group box 1 (HMGB1), a delayed mediator of proinflammatory cytokines, could initiate and amplify inflammatory responses to infection, injury, and other inflammatory stimuli, and it has emerged as a potential therapeutic target for inflammatory diseases. The overexpression of HMGB1 in endothelial cells has been proved to contribute to the development of these diseases. Because many proinflammatory cytokines expression were suppressed by thiazolidinediones (TZDs), agonists for nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ), whether TZDs can inhibit HMGB1 expression and function is of great interest, however, it remains unknown. Herein, we provide evidence that PPARγ agonist troglitazone, a member of the TZD class, modulates HMGB1 expression in the endothelial cell line EA.hy926 and propose a potential mechanism for that. Results from polymerase chain reaction experiments revealed that PPARγ is expressed in EA.hy926 cells, and it can be activated by troglitazone. Troglitazone inhibited the basal and LPS-stimulated HMGB1 expression at the mRNA level and protein level. A luciferase reporter assay showed that troglitazone inhibited not only the transcriptional activation of the HMGB1 promoter but also activities of heterologous promoters driven by nuclear factor κB (NF-κB) or activator protein 1 (AP-1) response elements. Altogether, these data suggest that NF-κB and AP-1 may participate in the inhibitory effect on HMGB1 transcription induced by troglitazone. Activation of PPARγ by troglitazone is effective for HMGB1 inhibition via suppressing NF-κB and AP-1 transcriptional activity in endothelial cells, which provides a new potential strategy to suppress excessive HMGB1 in inflammatory diseases.

GhHmgB3 deficiency deregulates proliferation and differentiation of cells during somatic embryogenesis in cotton

The proteins of high-mobility group box (HmgB) family were involved in the regulation of transcription and other DNA-dependent processes. To investigate the function of HmgB proteins during cotton somatic embryogenesis (SE), four Gossypium hirsutum HmgB genes were characterized. The gene GhHmgB3 preferentially expressed in embryonic tissues and was studied in detail. RNA interference and over-expression was used to regulate the expression of GhHmgB3 during cotton SE by transforming both hypocotyl and embryogenic calli (ECs) via Agrobacterium tumefaciens. The GhHmgB3-deficient somatic cells of hypocotyls dedifferentiated more vigorously than the control cells, but they failed to differentiate to ECs. In another case, the proliferation and differentiation of GhHmgB3-deficient ECs were significantly improved, but failed to form plantlets. Over-expression of GhHmgB3 had no significant differences in callus initiation and differentiation compared with the control cell lines. The different expression genes between the control and GhHmgB3-deficient ECs were identified by Solexa sequencing technology. The bioinformatics analysis and experimental verification revealed series of abnormal mechanism associated with β-catenin signalling. These results in response to the down-regulation of GhHmgB3 revealed series of β-catenin-related mechanisms might be responsible for the deregulation of proliferation and differentiation of cells in cotton SE.

The plant-specific family of DNA-binding proteins containing three HMG-box domains interacts with mitotic and meiotic chromosomes

• The high mobility group (HMG)-box represents a DNA-binding domain that is found in various eukaryotic DNA-interacting proteins. Proteins that contain three copies of the HMG-box domain, termed 3 × HMG-box proteins, appear to be specific to plants. The Arabidopsis genome encodes two 3 × HMG-box proteins that were studied here. • DNA interactions were examined using electrophoretic mobility shift assays, whereas expression, subcellular localization and chromosome association were mainly analysed by different types of fluorescence microscopy. • The 3 × HMG-box proteins bind structure specifically to DNA, display DNA bending activity and, in addition to the three HMG-box domains, the basic N-terminal domain contributes to DNA binding. The expression of the two Arabidopsis genes encoding 3 × HMG-box proteins is linked to cell proliferation. In synchronized cells, expression is cell cycle dependent and peaks in cells undergoing mitosis. 3 × HMG-box proteins are excluded from the nuclei of interphase cells and localize to the cytosol, but, during mitosis, they associate with condensed chromosomes. The 3 × HMG-box2 protein generally associates with mitotic chromosomes, while 3 × HMG-box1 is detected specifically at 45S rDNA loci. • In addition to mitotic chromosomes the 3 × HMG-box proteins associate with meiotic chromosomes, suggesting that they are involved in a general process of chromosome function related to cell division, such as chromosome condensation and/or segregation.

The expression level of the chromatin-associated HMGB1 protein influences growth, stress tolerance, and transcriptome in Arabidopsis

High mobility group (HMG) proteins of the HMGB family are small and relatively abundant chromatin-associated proteins. As architectural factors, the HMGB proteins are involved in the regulation of transcription and other DNA-dependent processes. We have examined Arabidopsis mutant plants lacking the HMGB1 protein, which is a typical representative of the plant HMGB family. In addition, our analyses included transgenic plants overexpressing HMGB1 and mutant plants that were transformed with the HMGB1 genomic region (complementation plants), as well as control plants. Both the absence and overexpression of HMGB1 caused shorter primary roots and affected the sensitivity towards the genotoxic agent methyl methanesulfonate. The overexpression of HMGB1 decreased the seed germination rate in the presence of elevated concentrations of NaCl. The complementation plants that expressed HMGB1 at wild-type levels did not show phenotypic differences compared to the control plants. Transcript profiling by microarray hybridization revealed that a remarkably large number of genes were differentially expressed (up- and down-regulated) in plants lacking HMGB1 compared to control plants. Among the down-regulated genes, the gene ontology category of stress-responsive genes was overrepresented. Neither microscopic analyses nor micrococcal nuclease digestion experiments revealed notable differences in overall chromatin structure, when comparing chromatin from HMGB1-deficient and control plants. Collectively, our results show that despite the presence of several other HMGB proteins, the lack and overexpression of HMGB1 affect certain aspects of plant growth and stress tolerance and it has a marked impact on the transcriptome, suggesting that HMGB1 has (partially) specialized functions in Arabidopsis.

Expression of a high mobility group protein isolated from Cucumis sativus affects the germination of Arabidopsis thaliana under abiotic stress conditions

Although high mobility group B (HMGB) proteins have been identified from a variety of plant species, their importance and functional roles in plant responses to changing environmental conditions are largely unknown. Here, we investigated the functional roles of a CsHMGB isolated from cucumber (Cucumis sativus L.) in plant responses to environmental stimuli. Under normal growth conditions or when subjected to cold stress, no differences in plant growth were found between the wild-type and transgenic Arabidopsis thaliana overexpressing CsHMGB. By contrast, the transgenic Arabidopsis plants displayed retarded germination compared with the wild-type plants when grown under high salt or dehydration stress conditions. Germination of the transgenic plants was delayed by the addition of abscisic acid (ABA), implying that CsHMGB affects germination through an ABA-dependent way. The expression of CsHMGB had affected only the germination stage, and CsHMGB did not affect the seedling growth of the transgenic plants under the stress conditions. The transcript levels of several germination-responsive genes were modulated by the expression of CsHMGB in Arabidopsis. Taken together, these results suggest that ectopic expression of a CsHMGB in Arabidopsis modulates the expression of several germination-responsive genes, and thereby affects the germination of Arabidopsis plants under different stress conditions.

Chromosomal high mobility group (HMG) proteins of the HMGB-type occurring in the moss Physcomitrella patens

High mobility group (HMG) proteins of the HMGB family are chromatin-associated proteins that act as architectural factors in nucleoprotein structures, which regulate DNA-dependent processes including transcription. Members of the HMGB family have been characterised from various mono-and dicot plants, but not from lower plant species. Here, we have identified three candidate HMGB proteins encoded in the genome of the moss Physcomitrella patens. The structurally similar HMGB2 and HMGB3 proteins display the typical overall structure of higher plant HMGB proteins consisting of a central HMG-box DNA-binding domain that is flanked by a basic N-terminal and an acidic C-terminal domain. The HMGB1 protein differs from higher plant HMGB proteins by having a very extensive N-terminal domain and by lacking the acidic C-terminal domain. Like higher plant HMGB proteins, HMGB3 localises to the cell nucleus, but HMGB1 is targeted to plastids. Analysis of the HMG-box domains of HMGB1 and HMGB3 by CD revealed that HMGB1box and the HMGB3box have an alpha-helical structure. While the HMGB3box interacts with DNA comparable to typical higher plant counterparts, the HMGB1box has only a low affinity for DNA. Cotransformation assays in Physcomitrella protoplasts demonstrated that expression of HMGB3 resulted in repression of reporter gene expression. In summary, our data show that functional HMGB-type proteins occur in Physcomitrella and most likely in other lower plant species.

Overlapping expression patterns among the genes encodingArabidopsischromosomal high mobility group (HMG) proteins

High mobility group (HMG) proteins are usually considered ubiquitous components of the eukaryotic chromatin. Using HMG gene promoter-GUS reporter gene fusions we have examined the expression of the reporter gene in transgenic Arabidopsis plants. These experiments have revealed that the different HMGA and HMGB promoters display overlapping patterns of activity, but they also show tissue- and developmental stage-specific differences. Moreover, leader introns that are present in some of the HMGB genes can modulate reporter gene expression. The differential HMG gene expression supports the view that the various HMG proteins serve partially different architectural functions in plant chromatin.

Characterization of Transgenic Arabidopsis Plants Overexpressing High Mobility Group B Proteins under High Salinity, Drought or Cold Stress

High mobility group B (HMGB) proteins found in the nuclei of higher eukaryotes play roles in various cellular processes such as replication, transcription and nucleosome assembly. The Arabidopsis thaliana genome contains eight genes encoding HMGB proteins, the functions of which remain largely unknown in the transcriptional regulation of plant stress responses. To understand better the functions of HMGB proteins in the responses of plants to environmental stimuli, we examined the effect of various abiotic stresses on germination and growth of transgenic Arabidopsis plants that overexpress a single isoform of HMGB. The expression of HMGB2, HMGB3 and HMGB4 was up-regulated by cold stress, whereas the expression of HMGB2 and HMGB3 was markedly down-regulated by drought or salt stress. Under salt or drought stress, the transgenic Arabidopsis plants that overexpress HMGB2 displayed retarded germination and subsequent growth compared with wild-type plants. Overexpression of HMGB4 had no impact on seed germination and seedling growth of the plants under the stress conditions tested. In contrast to no significant stress-related phenotypes of HMGB5-overexpressing plants, loss-of-function mutants of HMGB5 displayed retarded germination and subsequent growth compared with wild-type plants under stress conditions. Although transcript levels of various stress-responsive genes were not modulated by the expression of HMGB2, expression of several germination-responsive genes was modulated by HMGB2 under salt stress. Taken together, these results provide a novel basis for understanding the biological functions of HMGB protein family members that differently affect germination and seedling growth of Arabidopsis plants under various stress conditions.

Molecular cloning of a cDNA encoding a high mobility group protein in Cucumis sativus and its expression by abiotic stress treatments

A cDNA encoding a high mobility group B (HMGB) protein was isolated from Cucumis sativus and characterized with respect to its sequence, expression and responses to various abiotic stress treatments. The predicted polypeptide of 146 amino acid residues contains characteristic features of HMGB family proteins including the N-terminal basic region, one HMG-box and a stretch of acidic amino acid residues at the C-terminus. In vitro nucleic acid-binding assay revealed that the HMGB protein bound to both single-stranded DNA and double-stranded DNA. DNA gel blot analysis indicated that the HMGB gene is a single copy gene in cucumber genome. RNA gel blot analysis showed that the cucumber HMGB was more abundantly expressed in the roots than in shoots and leaves. Various abiotic stresses, including cold, drought and high salinity, down regulated markedly the expression of the HMGB in cucumber. The present report identifies a novel gene encoding HMGB protein in cucumber that shows a significant response to abiotic stress treatments.

High mobility group proteins of the plant HMGB family: dynamic chromatin modulators

In plants, the chromosomal high mobility group (HMG) proteins of the HMGB family typically contain a central HMG-box DNA-binding domain that is flanked by a basic N-terminal and an acidic C-terminal domain. The HMGB proteins are abundant and highly mobile proteins in the cell nucleus that influence chromatin structure and enhance the accessibility of binding sites to regulatory factors. Due to their remarkable DNA bending activity, HMGB proteins can increase the structural flexibility of DNA, promoting the assembly of nucleoprotein complexes that control DNA-dependent processes including transcription. Therefore, members of the HMGB family act as versatile modulators of chromatin function.

The Arabidopsis Genome Encodes Structurally and Functionally Diverse HMGB-type Proteins

The high mobility group (HMG) proteins of the HMGB family are chromatin-associated proteins that act as architectural factors in nucleoprotein structures, which regulate DNA-dependent processes including transcription and recombination. In addition to the previously identified HMGB1-HMGB6 proteins, the Arabidopsis genome encodes at least two other candidate family members (encoded by the loci At2g34450 and At5g23405) having the typical overall structure of a central domain displaying sequence similarity to HMG-box DNA binding domains, which is flanked by basic N-terminal and acidic C-terminal regions. Subcellular localisation experiments demonstrate that the At2g34450 protein is a nuclear protein, whereas the At5g23405 protein is found mainly in the cytoplasm. In line with this finding, At5g23405 displays specific interaction with the nuclear export receptor AtXPO1a. According to CD measurements, the HMG-box domains of both proteins have an alpha-helical structure. The HMG-box domain of At2g34450 interacts with linear DNA and binds structure-specifically to DNA minicircles, whereas the HMG-box domain of At5g23405 does not interact with DNA at all. In ligation experiments with short DNA fragments, the At2g34450 HMG-box domain can facilitate the formation of linear oligomers, but it does not promote the formation of DNA minicircles. Therefore, the At2g34450 protein shares several features with HMGB proteins, whereas the At5g23405 protein has different characteristics. Despite the presence of a region with similarity to the nucleosome-binding domain typical of HMGN proteins, At2g34450 does not bind nucleosome particles. In summary, our data demonstrate (i) that plant HMGB-type proteins are functionally variable and (ii) that it is difficult to predict HMG-box function solely based on sequence similarity.

Ectopic expression of the maize chromosomal HMGB1 protein causes defects in root development of tobacco seedlings

Chromatin-associated high mobility group (HMG) proteins of the HMGB family are versatile architectural factors assisting various DNA-dependent processes such as transcription and recombination. Here, transgenic tobacco lines were generated that ectopically express the maize HMGB1 protein, as detected by immunoblot analyses. The shoot morphology of HMGB1 expressing plants does not differ from that of control plants. By contrast, tobacco seedlings expressing HMGB1 are impaired in the growth of the primary root, relative to control plants. The reduced primary root length is correlated with the accumulation of small cells in the cell division zone (but not in the elongation zone) of the roots of transgenic plants. This "short-root" phenotype is specific for HMGB1, as is not observed with HMGB4 expressing plants, and it is transient in that it is restricted to young seedlings ( Collapse

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MESH Headings

• Cell Division
• Chromosomes, Plant/chemistry
• HMGB1 Protein/biosynthesis
• HMGB1 Protein/genetics
• HMGB1 Protein/metabolism
• HMGB1 Protein/physiology
• Microscopy, Fluorescence
• Plant Roots/growth & development
• Plant Roots/ultrastructure
• Plants, Genetically Modified/genetics
• Plants, Genetically Modified/growth & development
• Plants, Genetically Modified/metabolism
• Seedlings/growth & development
• Seedlings/metabolism
• Nicotiana/genetics
• Nicotiana/growth & development
• Nicotiana/metabolism
• Zea mays/chemistry
• Zea mays/genetics

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Affiliation(s)

Jacek Lichota Department of Life Sciences, Aalborg University, Sohngaardsholmsvej 49, DK-9000 Aalborg, Denmark
Christoph Ritt
Klaus D Grasser

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