Biomedical subjects

Woo Taek Kim

Publications and source records attributed to Woo Taek Kim.

At least 19 recordsLinked to original sources

PubMed2006

Heterologous expression and molecular and cellular characterization of CaPUB1 encoding a hot pepper U-Box E3 ubiquitin ligase homolog.

The U-box motif is a conserved domain found in the diverse isoforms of E3 ubiquitin ligase in eukaryotes. From water-stressed hot pepper (Capsicum annuum L. cv Pukang) plants, we isolated C. annuum putative U-box protein 1 (CaPUB1), which encodes a protein containing a single U-box motif in its N-terminal region. In vitro ubiquitination and site-directed mutagenesis assays revealed that CaPUB1 possessed E3 ubiquitin ligase activity and that the U-box motif was indeed essential for its enzyme activity. RNA gel-blot analysis showed that CaPUB1 mRNA was induced rapidly by a broad spectrum of abiotic stresses, including drought, high salinity, cold temperature, and mechanical wounding, but not in response to ethylene, abscisic acid, or a bacterial pathogen, suggesting its role in the early events in the abiotic-related defense response. Because transgenic work was extremely difficult in hot pepper, in this study we overexpressed CaPUB1 in Arabidopsis (Arabidopsis thaliana) to provide cellular information on the function of this gene in the development and plant responses to abiotic stresses. Transgenic Arabidopsis plants that constitutively expressed the CaPUB1 gene under the control of the cauliflower mosaic virus 35S promoter had markedly longer hypocotyls and roots and grew more rapidly than the wild type, leading to an early bolting phenotype. Microscopic analysis showed that 35S::CaPUB1 roots had increased numbers of small-sized cells, resulting in disordered, highly populated cell layers in the cortex, endodermis, and stele. In addition, CaPUB1-overexpressing plants displayed increased sensitivity to water stress and mild salinity. These results indicate that CaPUB1 is functional in Arabidopsis cells, thereby effectively altering cell and tissue growth and also the response to abiotic stresses. Comparative proteomic analysis showed that the level of RPN6 protein, a non-ATPase subunit of the 26S proteasome complex, was significantly reduced in 35SCaPUB1 seedlings as compared to the wild type. Pull-down and ubiquitination assays demonstrated that RPN6 interacted physically with CaPUB1 and was ubiquitinated in a CaPUB1-dependent manner in vitro. Although the physiological function of CaPUB1 is not yet clear, there are several possibilities for its involvement in a subset of physiological responses to counteract dehydration and high-salinity stresses in transgenic Arabidopsis seedlings.

Amino Acid Motifs↗

PubMed2006

Possible role of light in the maintenance of EIN3/EIL1 stability in Arabidopsis seedlings.

To examine the mechanism of EIN3-mediated gene expression by ethylene, the expression patterns of ethylene-inducible genes by ethylene were monitored in Col-0 and ethylene signaling mutants. In Col-0, the inducibility of ACC oxidase by ethylene in light-grown seedlings was much higher than in dark-grown seedlings. While the expression of ACC oxidase was highly increased by ethylene not only in Col-0 but in ein3-1 under light treatment, this pattern was completely abrogated in etiolated ein3-1 seedlings, suggesting the expression of EIN3-mediated ACC oxidase genes could be affected by light. To check if the level of EIN3 and EIL1 was regulated by light, cell-free degradation assays were performed. This resulted in the rapid degradation of these proteins within 1h after adding dark-grown cell extracts and this degradation was retarded by light-grown extracts. Here, we propose that light may act as a negative regulator in the destabilization of EIN3/EIL1.

Amino Acid Oxidoreductases↗

PubMed2006

Lys296 and Arg299 residues in the C-terminus of MD-ACO1 are essential for a 1-aminocyclopropane-1-carboxylate oxidase enzyme activity.

The 1-aminocyclopropane-1-carboxylate (ACC) oxidase catalyzes the last step in the biosynthesis of ethylene from ACC in higher plants. The complex structure of ACC oxidase/Fe(2+)/H(2)O derived from Petunia hybrida has recently been established by X-ray crystallography and it provides a vast structural information for ACC oxidase. Our mutagenesis study shows that both Lys296 and Arg299 residues in the C-terminal helix play important roles in enzyme activity. Both K296R and R299K mutant proteins retain only 30-15% of their enzyme activities with respect to that of the wild-type, implying that the positive charges of C-terminal residues are involved in enzymatic reaction. Furthermore, the sequence alignment of ACC oxidases from 24 different species indicates an existence of the exclusively conserved motif (Lys296-Glu301) especially in the C-terminus. The structure model based on our findings suggests that the positive-charged surface in the C-terminal helix of the ACC oxidase could be a major stabilizer in the spatial arrangement of reactants and that the positive-charge network between the active site and C-terminus is critical for ACC oxidase activity.

Amino Acid Oxidoreductases↗

PubMed2006

Mitochondria-associated hexokinases play a role in the control of programmed cell death in Nicotiana benthamiana.

Recent findings suggest a pivotal role for mitochondria-associated hexokinase in the regulation of apoptosis in animal cells. In this study, virus-induced gene silencing (VIGS) of a hexokinase-encoding Hxk1 caused necrotic lesions on leaves, abnormal leaf morphology, and retarded plant growth in Nicotiana benthamiana. Hxk1 was associated with the mitochondria, and this association required the N-terminal membrane anchor. VIGS of Hxk1 reduced the cellular glucose-phosphorylating activity to approximately 31% of control levels without changing the fructose-phosphorylating activity and did not alter hexose phosphate content severely. The affected cells showed programmed cell death (PCD) morphological markers, including nuclear condensation and DNA fragmentation. Similar to animal cell apoptosis, cytochrome c was released into the cytosol and caspase-9- and caspase-3-like proteolytic activities were strongly induced. Furthermore, based on flow cytometry, Arabidopsis thaliana plants overexpressing Arabidopsis HXK1 and HXK2, both of which are predominantly associated with mitochondria, exhibited enhanced resistance to H(2)O(2)- and alpha-picolinic acid-induced PCD. Finally, the addition of recombinant Hxk1 to mitochondria-enriched fractions prevented H(2)O(2)/clotrimazole-induced cytochrome c release and loss of mitochondrial membrane potential. Together, these results show that hexokinase critically regulates the execution of PCD in plant cells, suggesting a link between glucose metabolism and apoptosis.

Apoptosis↗

PubMed2006

Constitutive expression of abiotic stress-inducible hot pepper CaXTH3, which encodes a xyloglucan endotransglucosylase/hydrolase homolog, improves drought and salt tolerance in transgenic Arabidopsis plants.

Xyloglucan endotransglucosylase/hydrolase (XTH) has been recognized as a cell wall-modifying enzyme, participating in the diverse physiological roles. From water-stressed hot pepper plants, we isolated three different cDNA clones (pCaXTH1, pCaXTH2, and pCaXTH3) that encode XTH homologs. RT-PCR analysis showed that three CaXTH mRNAs were concomitantly induced by a broad spectrum of abiotic stresses, including drought, high salinity and cold temperature, and in response to stress hormone ethylene, suggesting their role in the early events in the abiotic-related defense response. Transgenic Arabidopsis plants that constitutively expressed the CaXTH3 gene under the control of the CaMV 35S promoter exhibited abnormal leaf morphology; the transgenic leaves showed variable degrees of twisting and bending along the edges, resulting in a severely wrinkled leaf shape. Microscopic analysis showed that 35S-CaXTH3 leaves had increased numbers of small-sized cells, resulting in disordered, highly populated mesophyll cells in each dorsoventral layer, and appeared to contain a limited amount of starch. In addition, the 35S-CaXTH3 transgenic plants displayed markedly improved tolerance to severe water deficit, and to lesser extent to high salinity in comparison with the wild-type plants. These results indicate that CaXTH3 is functional in heterologous Arabidopsis cells, thereby effectively altering cell growth and also the response to abiotic stresses. Although the physiological function of CaXTHs is not yet clear, there are several possibilities for their involvement in a subset of physiological responses to counteract dehydration and high salinity stresses in transgenic Arabidopsis plants.

Amino Acid Sequence↗

PubMed2006

Overexpression of carnation S-adenosylmethionine decarboxylase gene generates a broad-spectrum tolerance to abiotic stresses in transgenic tobacco plants.

Polyamines (PAs), such as putrescine, spermidine, and spermine, are present in all living organism and implicate in a wide range of cellular physiological processes. We have used transgenic technology in an attempt to evaluate their potential for mitigating the adverse effects of several abiotic stresses in plants. Sense construct of full-length cDNA for S-adenosylmethionine decarboxylase (SAMDC), a key enzyme in PA biosynthesis, from carnation (Dianthus caryophyllus L.) flower was introduced into tobacco (Nicotiana tabacum L.) by Agrobacterium tumefaciens-mediated transformation. Several transgenic lines overexpressing SAMDC gene under the control of cauliflower mosaic virus 35S promoter accumulated soluble total PAs by 2.2 (S16-S-4) to 3.1 (S16-S-1) times than wild-type plants. The transgenic tobacco did not show any difference in organ phenotype compared to the wild-type. The number and weight of seeds increased, and net photosynthetic rate also increased in transgenic plants. Stress-induced damage was attenuated in these transgenic plants, in the symptom of visible yellowing and chlorophyll degradation after all experienced stresses such as salt stress, cold stress, acidic stress, and abscisic acid treatment. H2O2-induced damage was attenuated by spermidine treatment. Transcripts for antioxidant enzymes (ascorbate peroxidase, manganase superoxide dismutase, and glutathione S-transferase) in transgenic plants and GUS activity transformed with SAMDC promoter::GUS fusion were induced more significantly by stress treatment, compared to control. These results that the transgenic plants with sense SAMDC cDNA are more tolerant to abiotic stresses than wild-type plants suggest that PAs may play an important role in contributing stress tolerance in plants.

Adaptation, Physiological↗

PubMed2006

Prohibitin is involved in mitochondrial biogenesis in plants.

Prohibitin, which consists of two subunits PHB1 and PHB2, plays a role in cell-cycle progression, senescence, apoptosis, and maintenance of mitochondrial function in mammals and yeast. In this study, we examined the role of prohibitins in plants by using virus-induced gene silencing (VIGS) of two prohibitin subunit genes of Nicotiana benthamiana, designated NbPHB1 and NbPHB2. NbPHB1 and NbPHB2 were targeted to the mitochondria, and their gene expression was suppressed during senescence. VIGS of NbPHB2 caused severe growth inhibition, leaf yellowing and symptoms of cell death, whereas VIGS of NbPHB1 resulted in a milder phenotype. At the cellular level, depletion of these subunits affected mitochondria by severely reducing their number and/or mass, and by causing morphological and physiological abnormalities. Suppression of prohibitin function resulted in a 10- to 20-fold higher production of reactive oxygen species and induced premature leaf senescence. Finally, disruption of prohibitin function rendered the plants more susceptible to various oxidative stress-inducing reagents, including H(2)O(2), paraquat, antimycin A and salicylic acid. These results suggest that prohibitins play a crucial role in mitochondrial biogenesis and protection against stress and senescence in plant cells.

DNA, Complementary↗

PubMed2005

Silencing of NbECR encoding a putative enoyl-CoA reductase results in disorganized membrane structures and epidermal cell ablation in Nicotiana benthamiana.

The very long chain fatty acids (VLCFAs) are synthesized by the microsomal fatty acid elongation system in plants. We investigated cellular function of NbECR putatively encoding enoyl-CoA reductase that catalyzes the last step of VLCFA elongation in Nicotiana benthamiana. Virus-induced gene silencing of NbECR produced necrotic lesions with typical cell death symptoms in leaves. In the affected tissues, ablation of the epidermal cell layer preceded disintegration of the whole leaf cell layers, and disorganized cellular membrane structure was evident. The amount of VLCFAs was reduced in the NbECR VIGS lines, suggesting NbECR function in elongation of VLCFAs. The results demonstrate that NbECR encodes a putative enoyl-CoA reductase and that the NbECR activity is essential for membrane biogenesis in N. benthamiana.

Amino Acid Sequence↗

PubMed2005

Functional characterization of NtCEF1, an AP2/EREBP-type transcriptional activator highly expressed in tobacco callus.

Using PCR-select cDNA subtraction, we identified the genes that are predominantly expressed in the shooty callus induced by suppression of the CHRK1 receptor-like kinase gene. One of the identified genes encoded a novel AP2/EREBP-type transcription factor, and it was highly expressed in various types of tobacco callus including the CHRK1 transgenic callus, hence designated as Nicotiana tabacum Callus-Expressing Factor 1 NtCEF1. The NtCEF1-GFP fusion protein was localized in the nucleus. The full length and the C-terminal acidic region of NtCEF1 could function as a transactivator in yeast, when fused to the LexA DNA binding domain. Expression of the NtCEF1 gene was induced by ethylene and by various abiotic stresses. Gel retardation assay revealed that NtCEF1 could bind specifically to the GCC box as well as to the C/DRE motif, albeit less strongly. Interestingly, NtCEF1 overexpression in Arabidopsis resulted in constitutive expression of various ethylene-responsive and defense genes that contain the GCC box in the promoter-but none of the genes containing the upstream C/DRE elements-indicating that NtCEF1 preferentially recognizes the GCC box in vivo. Furthermore, the NtCEF1-overexpressing Arabidopsis plants exhibited enhanced resistance to a bacterial pathogen, Pseudomonas syringae pv. tomato DC3000. Taken together, these results suggest that NtCEF1 is a transcription factor preferentially activating the GCC box-containing defense genes, and that it modulates increased resistance against the biotic stress by activation of the downstream gene expression.

Amino Acid Sequence↗

PubMed2005

Relationship between atopic status and nasal interleukin 10 and 11 levels in infants with respiratory syncytial virus bronchiolitis.

BACKGROUND: Interleukin 10 (IL-10) and IL-11 are known to have anti-inflammatory activities, and they have been implicated in the pathogenesis of respiratory syncytial virus (RSV) infection. OBJECTIVES: To determine IL-10, IL-11, and myeloperoxidase levels in nasal secretions of infants with acute RSV bronchiolitis and to investigate whether there are any differences in these levels in patients with vs without atopy. METHODS: We measured IL-10, IL-11, and myeloperoxidase levels in nasal secretions of 44 infants (20 were atopic) with acute RSV bronchiolitis. The nasal secretion samples were obtained from patients at hospital admission and were stored immediately at -70 degrees C until analysis. Atopy was defined as having at least 1 positive skin prick test reaction to common allergens, a history of atopic dermatitis, or a high serum IgE level compared with age-matched controls. RESULTS: Levels of IL-10, IL-11, and myeloperoxidase increased significantly in samples from infants with acute RSV bronchiolitis. Levels of IL-10 and IL-11 were significantly lower in patients with vs without atopy (P < .05). Myeloperoxidase levels showed no significant difference in patients with vs without atopy (P = .18). Patients with severe symptoms tended to have lower IL-10 levels (P = .09), but no relationship was shown between symptom severity and IL-11 levels. Nasal myeloperoxidase levels were significantly higher in patients with severe symptoms (P < .05). CONCLUSIONS: Production of IL-10 and IL-11 was significantly lower in patients with vs without atopy during acute RSV bronchiolitis. The airway inflammation induced by RSV infection may be different in patients with vs without atopy, and this is associated with lower induction of these immunoregulatory cytokines in children with atopy.

Bodily Secretions↗

PubMed2005

Retinoblastoma protein regulates cell proliferation, differentiation, and endoreduplication in plants.

Retinoblastoma protein (Rb) plays a key role in cell cycle control, cell differentiation, and apoptosis in animals. In this study, we used virus-induced gene silencing (VIGS) to investigate the cellular functions of Rb in higher plants. VIGS of NbRBR1, which encodes the Nicotiana benthamiana Rb homolog, resulted in growth retardation and abnormal organ development. At the cellular level, Rb suppression caused prolonged cell proliferation in tissues that are normally differentiated, which indicates that Rb is a negative regulator of plant cell division. Furthermore, differentiation of the epidermal pavement cells and trichomes was partially retarded, and stomatal clusters formed in the epidermis, likely due to uncontrolled cell division of stomata precursor cells. Rb suppression also caused extra DNA replication in endoreduplicating leaf cells, suggesting a role of Rb in the endocycle. These Rb phenotypes were accompanied by stimulated transcription of E2F and E2F-regulated S-phase genes. Thus, disruption of Rb function in plants leads to ectopic cell division in major organs that correlates with a delay in cell differentiation as well as increased endoreduplication, which indicates that Rb coordinates these processes in plant organ development.

Cell Differentiation↗

PubMed2004

Isolation and functional characterization of the Ca-DREBLP1 gene encoding a dehydration-responsive element binding-factor-like protein 1 in hot pepper (Capsicum annuum L. cv. Pukang).

Through the use of subtractive hybridization analysis, we have identified 14 partial cDNA clones (pCa-DSRs) that are rapidly induced by dehydration in hot pepper (Capsicum annuum L.) roots. The predicted proteins encoded by Ca-DSRs are putatively involved in processes as diverse as primary and secondary metabolism, protein degradation, and stress responses, indicating the complexity of cellular responses to water deficit in hot pepper roots. Particularly, we investigated the detailed structural properties and expression profiles of Ca-DSR2 (Ca-DREBLP1: dehydration-responsive element binding-factor-like protein 1) encoding a protein that contains a single ERF/AP2 DNA-binding domain. Based on the conserved 14th valine and 19th glutamic acid residues in the ERF/AP2 domain, a basic amino acid stretch (PKKPAGRKKFR) near its N-terminal region, and DSAW signature sequence at the end of its ERF/AP2 domain, Ca-DREBLP1 was classified as a member of a DREB1-type subfamily. Gel retardation assays revealed that Ca-DREBLP1 was able to form a specific complex with the DRE/CRT motif, but not with the GCC box. When fused to the GAL4 DNA-binding domain, the Ca-DREBLP1(190-215) mutant could effectively function as a trans-activator in yeast. This suggests that the extreme C-terminal region plays an essential role in transcription activation. In hot pepper plants, Ca-DREBLP1 was rapidly induced by dehydration, high salinity and, to a lesser extent, mechanical wounding, but not by cold stress. Thus, although the structural features of Ca-DREBLP1 resemble those of the DREB1-type proteins of Arabidopsis thaliana and rice plants, its induction patterns are reminiscent of the DREB2-type proteins, indicating that Ca-DREBLP1 is a novel class DREB subfamily in hot pepper.

Amino Acid Sequence↗

PubMed2004

Perturbation of NgTRF1 expression induces apoptosis-like cell death in tobacco BY-2 cells and implicates NgTRF1 in the control of telomere length and stability.

Telomeres are specialized nucleoprotein complexes that are essential for preserving chromosome integrity in eukaryotic cells. Several potential telomere binding proteins have recently been identified in higher plants, but nothing is known about their in vivo functions. We previously identified NgTRF1 as a double-stranded telomeric repeat binding factor in tobacco (Nicotiana tabacum) and here show that the binding of NgTRF1 to telomeric repeats inhibits telomerase-mediated telomere extension. To determine whether NgTRF1 is involved in telomere length regulation, we established transgenic tobacco BY-2 cell lines that overexpress or suppress NgTRF1. Pulsed-field gel electrophoresis showed that 35S::NgTRF1 cells exhibited significantly shortened telomeres (45 to 10 kb), whereas 35S::antisense-NgTRF1 cells contained longer telomeres (80 to 25 kb) compared with wild-type and 35S::GUS control cells (65 to 15 kb), indicating that telomere length inversely correlates with the amount of functional NgTRF1 in BY-2 cells. 35S::NgTRF1 cells with shorter telomeres displayed a progressive reduction in cell viability and stopped dividing after 25 to 40 successive rounds of 12-d batch subculture, in sharp contrast with control cells, which have an unlimited capacity for division. Internucleosomal DNA fragmentation, mitochondrial release of cytochrome c, and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling positive nuclei were detected in 35S::NgTRF1 cells during prolonged subculture, indicating that enhanced cell death was attributable to an apoptosis-like mechanism. 35S::antisense-NgTRF1 cells containing low levels of NgTRF1 also exhibited a progressive decrease in cell viability and apoptotic cell death, but less so than did 35S::NgTRF1 cells, suggesting that the level of NgTRF1 is critically associated with cell viability. Taken together, these data indicate that perturbation of NgTRF1 expression results in changes in telomere length and stability, which in turn causes apoptotic cell death in transgenic BY-2 cells. These results are discussed in light of the suggestion that NgTRF1 is involved in the mechanism by which telomere length and stability are maintained. We further suggest that the structural stability of telomeres, in addition to length maintenance, is essential for their function and for the immortality of BY-2 cells.

Apoptosis↗

PubMed2004

The CaPRP1 gene encoding a putative proline-rich glycoprotein is highly expressed in rapidly elongating early roots and leaves in hot pepper (Capsicum annuum L. cv. Pukang).

Most of the proline-rich cell wall glycoprotein genes isolated from higher plants are preferentially expressed in the transmitting tissues of the flower organ. In conducting expressed sequence tag (EST) analysis, which was prepared from 5-day-old early roots of hot pepper (Capsicum annuum L. cv. Pukang), we identified a cDNA clone, pCaPRP1, encoding a putative cell wall proline-rich glycoprotein. CaPRP1 (Mr=28 kDa, pI=9.98) was most closely related to Nicotiana alata NaPRP4 (71%), while most distantly related to soybean PvPRP (37%). The predicted primary structure of CaPRP1 contains a putative N-terminal signal peptide, six repeats of the Lys-Pro-Pro tripeptide, four repeats of a five-amino acid sequence [Pro-(Ser/The)-Pro-Pro-Pro] and one potential N-glycosylation site (Asn-Asn-Ser). In contrast to most proline-rich cell wall glycoprotein genes, CaPRP1 was highly expressed in rapidly elongating very early roots and young leaves as well as developing flower tissues. Although the physiological function of CaPRP1 is not yet clear, there are several possibilities for its role in cell expansion and elongation during early development of hot pepper plants.

Amino Acid Sequence↗

PubMed2004

The active site and substrate-binding mode of 1-aminocyclopropane-1-carboxylate oxidase determined by site-directed mutagenesis and comparative modelling studies.

The active site and substrate-binding mode of MD-ACO1 (Malus domestica Borkh. 1-aminocyclopropane-1-carboxylate oxidase) have been determined using site-directed mutagenesis and comparative modelling methods. The MD-ACO1 protein folds into a compact jelly-roll motif comprised of eight a-helices, 12 b-strands and several long loops. The active site is well defined as a wide cleft near the C-terminus. The co-substrate ascorbate is located in cofactor Fe2+-binding pocket, the so-called '2-His-1-carboxylate facial triad'. In addition, our results reveal that Arg244 and Ser246 are involved in generating the reaction product during enzyme catalysis. The structure agrees well with the biochemical and site-directed mutagenesis results. The three-dimensional structure together with the steady-state kinetics of both the wild-type and mutant MD-ACO1 proteins reveal how the substrate specificity of MD-ACO1 is involved in the catalytic mechanism, providing insights into understanding the fruit ripening process at atomic resolution.

Amino Acid Oxidoreductases↗

PubMed2004

Capsicum annuum tobacco mosaic virus-induced clone 1 expression perturbation alters the plant's response to ethylene and interferes with the redox homeostasis.

Capsicum annuum tobacco mosaic virus (TMV)-induced clone 1 (CaTin1) gene was expressed early during incompatible interaction of hot pepper (Caspsicum annuum) plants with TMV and Xanthomonas campestris. RNA-blot analysis showed that CaTin1 gene was expressed only in roots in untreated plants and induced mainly in leaf in response to ethylene, NaCl, and methyl viologen but not by salicylic acid and methyl jasmonate. The ethylene dependence of CaTin1 induction upon TMV inoculation was demonstrated by the decrease of CaTin1 expression in response to several inhibitors of ethylene biosynthesis or its action. Transgenic tobacco (Nicotiana tabacum) plants expressing CaTin1 gene in sense- or antisense-orientation showed interesting characteristics such as the accelerated growth and the enhanced resistance to biotic as well as abiotic stresses. Such characteristics appear to be caused by the elevated level of ethylene and H2O2. Moreover, in transgenic plants expressing antisense CaTin1 gene, the expression of some pathogenesis-related genes was enhanced constitutively, which may be mainly due to the increased ethylene level. The promoter of CaTin1 has four GCC-boxes, two AT-rich regions, and an elicitor-inducible W-box. The induction of the promoter activity by ethylene depends on GCC-boxes and by TMV on W-box. Taken together, we propose that the CaTin1 up-regulation or down-regulation interferes with the redox balance of plants leading to the altered response to ethylene and biotic as well as abiotic stresses.

Acetates↗

PubMed2004

A proteomic analysis identifies glutathione S-transferase isoforms whose abundance is differentially regulated by ethylene during the formation of early root epidermis in Arabidopsis seedlings.

The plant hormone ethylene has been shown to play an important role in root hair development in Arabidopsis. With the aid of proteomic analysis, we identified three distinct glutathione S-transferase (GST) isoforms, AtGSTF2, AtGSTF8, and AtGSTU19, expressed early in root epidermal establishment in Arabidopsis seedlings. The AtGSTF2 protein was specifically up-regulated by ethylene. A subsequent RNA expression study revealed that the AtGSTF2 gene was highly sensitive to ethylene, whereas the transcripts for AtGSTF8 and AtGSTU19 were constitutively present in new root tissue of 4-day-old seedlings. The steady-state level of AtGSTF2 mRNA was greatly reduced in the roots of ethylene-insensitive mutants, while mutation at the CTR1 locus, which confers an ectopic root hair phenotype, resulted in a markedly elevated level of AtGSTF2 transcript in young root tissue. Although the physiological function of ethylene-induced AtGSTF2 is not yet clear, there are several possibilities for its role during early root development.

Amino Acids, Cyclic↗

PubMed2004

Light differentially regulates the expression of two members of the auxin-induced 1-aminocyclopropane-1-carboxylate synthase gene family in mung bean (Vigna radiata L.) seedlings.

Auxin induces the expression of the two ethylene-biosynthetic genes VR-ACS6 and VR-ACS7 in etiolated mung bean hypocotyls. However, while it also enhances VR-ACS6 expression in light-grown tissues, it does not up-regulate VR-ACS7 expression in these tissues. Here we show that transfer of 3-day-old etiolated seedlings into light quickly reduced the auxin-induced expression of both genes. However, while auxin-induced VR-ACS6 expression recovered after 24 h of light, VR-ACS7 transcription continued to reduce and was almost completely absent at 36 h. Thus, light differentially modulates the expression of the auxin-inducible VR-ACS genes. In hormone-treated etiolated seedlings, VR-ACS7 was primarily induced in the rapidly elongating zones of hypocotyl and epicotyl tissues, while auxin-induced VR-ACS6 mRNA was evenly distributed throughout the whole seedling. VR-ACS7 promoter-driven beta-glucuronidase (GUS) activity in auxin-treated etiolated transgenic Arabidopsis seedlings was observed in the highly elongating zones of the hypocotyl. During de-etiolation, the GUS activity gradually declined to become confined to the uppermost region of hypocotyls. In situ mRNA localization studies showed that in etiolated mung bean hypocotyls, the auxin-dependent VR-ACS7 transcript was predominantly present in the epidermis, which is the driving site for auxin-mediated elongation. Thus, it appears that the modulation by light of auxin-induced VR-ACS7 expression may correlate closely with the elongation growth response in early seedling development.

Arabidopsis↗