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At least 613 records · Page 34Linked to original sources
PubMed2001

Rerouting the plant phenylpropanoid pathway by expression of a novel bacterial enoyl-CoA hydratase/lyase enzyme function.

The gene for a bacterial enoyl-CoA hydratase (crotonase) homolog (HCHL) previously shown to convert 4-coumaroyl-CoA, caffeoyl-CoA, and feruloyl-CoA to the corresponding hydroxybenzaldehydes in vitro provided an opportunity to subvert the plant phenylpropanoid pathway and channel carbon flux through 4-hydroxybenzaldehyde and the important flavor compound 4-hydroxy-3-methoxybenzaldehyde (vanillin). Expression of the Pseudomonas fluorescens AN103 HCHL gene in two generations of tobacco plants caused the development of phenotypic abnormalities, including stunting, interveinal chlorosis and senescence, curled leaf margins, low pollen production, and male sterility. In second generation progeny, the phenotype segregated with the transgene and transgenic siblings exhibited orange/red coloration of the vascular ring, distorted cells in the xylem and phloem bundles, and lignin modification/reduction. There was depletion of the principal phenolics concomitant with massive accumulation of novel metabolites, including the glucosides and glucose esters of 4-hydroxybenzoic acid and vanillic acid and the glucosides of 4-hydroxybenzyl alcohol and vanillyl alcohol. HCHL plants exhibited increased accumulation of transcripts for phenylalanine ammonia-lyase, cinnamate-4-hydroxylase, and 4-coumarate:CoA ligase, whereas beta-1,3-glucanase was suppressed. This study, exploiting the ability of a bacterial gene to divert plant secondary metabolism, provides insight into how plants modify inappropriately accumulated metabolites and reveals the consequences of depleting the major phenolic pools.

Acyl Coenzyme A↗
PubMed2002

The gibberellin signaling pathway is regulated by the appearance and disappearance of SLENDER RICE1 in nuclei.

The slender rice1 mutant (slr1) shows a constitutive gibberellin (GA) response phenotype. To investigate the mode of action of SLR1, we generated transgenic rice expressing a fusion protein consisting of SLR1 and green fluorescent protein (SLR1-GFP) and analyzed the phenotype of the transformants and the subcellular localization of GFP in vivo. SLR1-GFP worked in nuclei to repress the GA signaling pathway; its overproduction caused a dwarf phenotype. Application of GA(3) to SLR1-GFP overproducers induced GA actions such as shoot elongation, downregulation of GA 20-oxidase expression, and upregulation of SLR1 expression linked with the disappearance of the nuclear SLR1-GFP protein. We also performed domain analyses of SLR1 using transgenic plants overproducing different kinds of truncated SLR1 proteins. The analyses revealed that the SLR1 protein can be divided into four parts: a GA signal perception domain located at the N terminus, a regulatory domain for its repression activity, a dimer formation domain essential for signal perception and repression activity, and a repression domain at the C terminus. We conclude that GA signal transduction is regulated by the appearance or disappearance of the nuclear SLR1 protein, which is controlled by the upstream GA signal.

Arabidopsis Proteins↗
PubMed2002

Arabidopsis RGL1 encodes a negative regulator of gibberellin responses.

In Arabidopsis, the DELLA subfamily of GRAS regulatory genes consists of GAI, RGA, RGA-LIKE1 (RGL1), RGL2, and RGL3. GAI and RGA are known to be negative regulators of gibberellin (GA) responses. We found that RGL1 is a similar repressor of GA responses, as revealed by RGL1 gain-of-function and loss-of-function phenotypes. Repression of GA responses in Arabidopsis was conferred by a dominant 35S-rgl1 transgene carrying a DELLA domain deletion analogous to the GA-insensitive gai-1 mutation. As in GA-deficient Arabidopsis, the transgenic plants were dark green dwarfs with underdeveloped trichomes and flowers. Expression levels of GA4, a feedback-regulated GA biosynthetic gene, were increased correspondingly. Conversely, a loss-of-function rgl1 line had reduced GA4 expression and exhibited GA-independent activation of seed germination, leaf expansion, flowering, stem elongation, and floral development, as detected by resistance to the GA biosynthesis inhibitor paclobutrazol. RGL1 plays a greater role in seed germination than do GAI and RGA. The expression profile of RGL1 differed from those of the four other DELLA homologs. RGL1 message levels were predominant in flowers, with transcripts detected in developing ovules and anthers. As with RGA, green fluorescent protein (GFP)-tagged RGL1 protein was localized to the nucleus, but unlike GFP-RGA, there was no degradation after GA treatment. These findings indicate that RGL1 is a partially redundant, but distinct, negative regulator of GA responses and suggest that all DELLA subfamily members might possess separate as well as overlapping roles in GA signaling.

Amino Acid Sequence↗
PubMed2002

The Arabidopsis Rop2 GTPase is a positive regulator of both root hair initiation and tip growth.

Root hairs provide a model system for the study of cell polarity. We examined the possibility that one or more members of the distinct plant subfamily of RHO monomeric GTPases, termed Rop, may function as molecular switches regulating root hair growth. Specific Rops are known to control polar growth in pollen tubes. Overexpressing Rop2 (Rop2 OX) resulted in a strong root hair phenotype, whereas overexpressing Rop7 appeared to inhibit root hair tip growth. Overexpressing Rops from other phylogenetic subgroups of Rop did not give a root hair phenotype. We confirmed that Rop2 was expressed throughout hair development. Rop2 OX and constitutively active GTP-bound rop2 (CA-rop2) led to additional and misplaced hairs on the cell surface as well as longer hairs. Furthermore, CA-rop2 depolarized root hair tip growth, whereas Rop2 OX resulted in hairs with multiple tips. Dominant negative GDP-bound Rop2 reduced the number of hair-forming sites and led to shorter and wavy hairs. Green fluorescent protein-Rop2 localized to the future site of hair formation well before swelling formation and to the tip throughout hair development. We conclude that the Arabidopsis Rop2 GTPase acts as a positive regulatory switch in the earliest visible stage in hair development, swelling formation, and in tip growth.

Actins↗
PubMed2003

The Arabidopsis LATERAL ORGAN BOUNDARIES-domain gene ASYMMETRIC LEAVES2 functions in the repression of KNOX gene expression and in adaxial-abaxial patterning.

The normal development of lateral organs of the shoot requires the simultaneous repression of meristem-specific genes and the activation of organ-specific genes. ASYMMETRIC LEAVES2 (AS2) is required for the development of normal leaf shape and for the repression of KNOX genes in the leaf. AS2 is a member of the recently identified, plant-specific LATERAL ORGAN BOUNDARIES (LOB)-domain gene family. Expression of AS2 at high levels resulted in repression of the KNOX homeobox genes BREVIPEDICELLUS, KNAT2, and KNAT6 but not of the related SHOOT MERISTEMLESS gene. Overexpression of AS2 also led to a perturbation of normal adaxial-abaxial asymmetry in lateral organs, resulting in the replacement of abaxial cell types with adaxial cell types. These results indicate that AS2 is sufficient to induce adaxial cell fate and repress KNOX gene expression.

Arabidopsis↗
PubMed2004

Enod40, a short open reading frame-containing mRNA, induces cytoplasmic localization of a nuclear RNA binding protein in Medicago truncatula.

In eukaryotes, diverse mRNAs containing only short open reading frames (sORF-mRNAs) are induced at specific stages of development. Their mechanisms of action may involve the RNA itself and/or sORF-encoded oligopeptides. Enod40 genes code for highly structured plant sORF-mRNAs involved in root nodule organogenesis. A novel RNA binding protein interacting with the enod40 RNA, MtRBP1 (for Medicago truncatula RNA Binding Protein 1), was identified using a yeast three-hybrid screening. Immunolocalization studies and use of a MtRBP1-DsRed2 fluorescent protein fusion showed that MtRBP1 localized to nuclear speckles in plant cells but was exported into the cytoplasm during nodule development in enod40-expressing cells. Direct involvement of the enod40 RNA in MtRBP1 relocalization into cytoplasmic granules was shown using a transient expression assay. Using a (green fluorescent protein)/MS2 bacteriophage system to tag the enod40 RNA, we detected in vivo colocalization of the enod40 RNA and MtRBP1 in these granules. This in vivo approach to monitor RNA-protein interactions allowed us to demonstrate that cytoplasmic relocalization of nuclear proteins is an RNA-mediated cellular function of a sORF-mRNA.

Amino Acid Sequence↗
PubMed2000

Cosuppression of a plasma membrane H(+)-ATPase isoform impairs sucrose translocation, stomatal opening, plant growth, and male fertility.

The plasma membrane H(+)-ATPase builds up a pH and potential gradient across the plasma membrane, thus activating a series of secondary ion and metabolite transporters. pma4 (for plasma membrane H(+)-ATPase 4), the most widely expressed H(+)-ATPase isogene in Nicotiana plumbaginifolia, was overexpressed in tobacco. Plants that overexpressed PMA4 showed no major changes in plant growth under normal conditions. However, two transformants were identified by their stunted growth, slow leaf initiation, delayed stem bolting and flowering, and male sterility. Protein gel blot analysis showed that expression of the endogenous and transgenic pma4 was cosuppressed. Cosuppression was developmentally regulated because PMA4 was still present in developing leaves but was not detected in mature leaves. The glucose and fructose content increased threefold, whereas the sucrose content remained unchanged. The rate of sucrose exudation from mature leaves was reduced threefold and the sugar content of apical buds was reduced twofold, suggesting failure of sucrose loading and translocation to the sink tissues. Cosuppression of PMA4 also affected the guard cells, stomatal opening, and photosynthesis in mature leaves. These results show that a single H(+)-ATPase isoform plays a major role in several transport-dependent physiological processes.

Biological Transport↗
PubMed2000

A shaker-like K(+) channel with weak rectification is expressed in both source and sink phloem tissues of Arabidopsis.

RNA gel blot and reverse transcription-polymerase chain reaction experiments were used to identify a single K(+) channel gene in Arabidopsis as expressed throughout the plant. Use of the beta-glucuronidase reporter gene revealed expression of this gene, AKT2/AKT3, in both source and sink phloem tissues. The AKT2/AKT3 gene corresponds to two previously identified cDNAs, AKT2 (reconstructed at its 5' end) and AKT3, the open reading frame of the latter being shorter at its 5' end than that of the former. Rapid amplification of cDNA ends with polymerase chain reaction and site-directed mutagenesis was performed to identify the initiation codon for AKT2 translation. All of the data are consistent with the hypothesis that the encoded polypeptide corresponds to the longest open reading frame previously identified (AKT2). Electrophysiological characterization (macroscopic and single-channel currents) of AKT2 in both Xenopus oocytes and COS cells revealed a unique gating mode and sensitivity to pH (weak inward rectification, inhibition, and increased rectification upon internal or external acidification), suggesting that AKT2 has enough functional plasticity to perform different functions in phloem tissue of source and sink organs. The plant stress hormone abscisic acid was shown to increase the amount of AKT2 transcript, suggesting a role for the AKT2 in the plant response to drought.

Amino Acid Sequence↗
PubMed2000

Prenylation of the floral transcription factor APETALA1 modulates its function.

The Arabidopsis MADS box transcription factor APETALA1 (AP1) was identified as a substrate for farnesyltransferase and shown to be farnesylated efficiently both in vitro and in vivo. AP1 regulates the transition from inflorescence shoot to floral meristems and the development of sepals and petals. AP1 fused to green fluorescent protein (GFP) retained transcription factor activity and directed the expected terminal flower phenotype when ectopically expressed in transgenic Arabidopsis. However, ap1mS, a farnesyl cysteine-acceptor mutant of AP1, as well as the GFP-ap1mS fusion protein failed to direct the development of compound terminal flowers but instead induced novel phenotypes when ectopically expressed in Arabidopsis. Similarly, compound terminal flowers did not develop in era1-2 transformants that ectopically expressed AP1. Together, the results demonstrate that AP1 is a target of farnesyltransferase and suggest that farnesylation alters the function and perhaps specificity of the transcription factor.

Alkyl and Aryl Transferases↗
PubMed2001

Activation of the Arabidopsis B class homeotic genes by APETALA1.

Proper development of petals and stamens in Arabidopsis flowers requires the activities of APETALA3 (AP3) and PISTILLATA (PI), whose transcripts can be detected in the petal and stamen primordia. Localized expression of AP3 and PI requires the activities of at least three genes: APETALA1 (AP1), LEAFY (LFY), and UNUSUAL FLORAL ORGANS (UFO). It has been proposed that UFO provides spatial cues and that LFY specifies competence for AP3 and PI expression in the developing flower. To understand the epistatic relationship among AP1, LFY, and UFO in regulating AP3 and PI expression, we generated two versions of AP1 that have strong transcriptional activation potential. Genetic and molecular analyses of transgenic plants expressing these activated AP1 proteins show that the endogenous AP1 protein acts largely as a transcriptional activator in vivo and that AP1 specifies petals by regulating the spatial domains of AP3 and PI expression through UFO.

Arabidopsis↗
PubMed2006

Allergic contact dermatitis to plants in a Spanish dermatology department: a 7-year review.

To investigate the incidence of allergic contact dermatitis (ACD) to plants in our area, we reviewed the records of the patients that were studied in the Allergic Contact Unity of our hospital in the last 7 years (2248 patients). We found 69 cases of positive patch tests to plant allergens, representing 3% of all the patients in that period. Diallyl disulfide was the most frequent allergen (47 cases), involving mainly middle-aged housewives with chronic hand eczema. Positive tests to sesquiterpene lactone mix (SL mix) were found in 11 patients, mostly middle-aged rural workmen with an airborne clinical pattern. Other allergens detected were lichens, primin, tulipalin A and wood. These results show a high incidence of ACD to diallyl disulfide that, in our opinion, should be tested in all housewives or cooks with chronic hand eczema. The predominance of the classical airborne pattern of allergy to SL in our study may be because the airborne way of allergen exposure in our area, with a high percentage of rural population, is the most frequent, and it makes it important to remember this possibility in the differential diagnosis of photosensitivity.

Adult↗
PubMed1995

The gravitropic set-point angle (GSA): the identification of an important developmentally controlled variable governing plant architecture.

The angle at which an organ is maintained by gravitropism is characteristic of the organ, its developmental state and the prevailing environmental conditions. We propose that this angle be called the gravitropic set-point angle (GSA), defined as the angle with respect to the gravity vector (with a vertically downward orientation being 0 degrees) at which an organ is maintained as a consequence of gravitropism. Studies or the gravitropic behaviour of organs from trailing plants show that the GSA is subject to developmental regulation. Depending on the developmental age and prevailing environmental conditions, the GSA of an organ can be set at any value between 0 degrees and 180 degrees. The previously reported reversal of the sign of the gravitropic response in such organs, whether this is brought about developmentally or induced by light, represents the change from one common extreme (GSA = 180 degrees, conventionally referred to as negative orthogravitropism) to another (GSA = 0 degrees, or positive orthogravitropism). The concept of a variable gravitropic set-point offers a more unified view of all forms of gravitropic behaviour than has been advanced previously, and places a new constraint on models of gravitropism. Current models of gravitropism appear to be unable to explain either the ability of organs to change their orientation with respect to gravity as they develop, or the re-orientation that can be observed when some organs are exposed to new environmental conditions.

Darkness↗
PubMed2005

Expression of GFP-fusions in Arabidopsis companion cells reveals non-specific protein trafficking into sieve elements and identifies a novel post-phloem domain in roots.

Transgenic Arabidopsis plants were constructed to express a range of GFP-fusion proteins (36-67 kDa) under the companion cell (CC)-specific AtSUC2 promoter. These plants were used to monitor the trafficking of these GFP-fusion proteins from the CCs into the sieve elements (SEs) and their subsequent translocation within and out of the phloem. The results revealed a large size exclusion limit (SEL) (>67 kDa) for the plasmodesmata connecting SEs and CCs in the loading phloem. Membrane-anchored GFP-fusions and a GFP variant targeted to the endoplasmic reticulum (ER) remained inside the CCs and were used as 'zero trafficking' controls. In contrast, free GFP and all soluble GFP-fusions, moved from the CCs into the SEs and were subsequently translocated through the phloem. Phloem unloading and post-phloem transport of these mobile GFP-fusions were studied in root tips, where post-phloem transport occurred only for the free form of GFP. All of the other soluble GFP-fusion variants were unloaded and restricted to a narrow zone of cells immediately adjacent to the mature protophloem. It appears that this domain of cells, which has a peripheral SEL of about 27-36 kDa, allows protein exchange between protophloem SEs and surrounding cells, but restricts general access of large proteins into the root tip. The presented data provide additional information on phloem development in Arabidopsis in relation to the formation of symplasmic domains.

Arabidopsis↗
PubMed2005

Expression systems and developments in plant-made vaccines.

Delivery of vaccines to mucosal surfaces can elicit humoral and cell-mediated responses of the mucosal and systemic immune systems, evoke less pain and discomfort than parenteral delivery, and eliminate needle-associated risks. Transgenic plants are an ideal means by which to produce oral vaccines, as the rigid walls of the plant cell protect antigenic proteins from the acidic environment of the stomach, enabling intact antigen to reach the gut associated lymphoid tissue. In the past few years, new techniques (such as chloroplast transformation and food processing) have improved antigen concentration in transgenic plants. In addition, adjuvants and targeting proteins have increased the immunogenicity of mucosally administered plant-made vaccines. These studies have moved plant-made vaccines closer to the development phase.

Administration, Oral↗
PubMed2004

Antifungal activity of Thymus oils and their major compounds.

The increasing recognition and importance of fungal infections, the difficulties encountered in their treatment and the increase in resistance to antifungals have stimulated the search for therapeutic alternatives. Essential oils have been used empirically. The essential oils of Thymus (Thymus vulgaris, T. zygis subspecies zygis and T. mastichina subspecies mastichina) have often been used in folk medicine. The aim of the present study was to evaluate objectively the antifungal activity of Thymus oils according to classical bacteriological methodologies - determination of the minimal inhibitory concentration (MIC) and the minimal lethal concentration (MLC) - as well as flow cytometric evaluation. The effect of essential oils upon germ tube formation, an important virulence factor, was also studied. The mechanism of action was studied by flow cytometry, after staining with propidium iodide. The chemical composition of the essential oils was investigated by gas chromatography (GC) and gas chromatography/mass spectroscopy (GC/MS). The antifungal activity of the major components (carvacrol, thymol, p-cymene and 1,8-cineole) and also possible interactions between them were also investigated. The essential oils of T. vulgaris and T. zygis showed similar antifungal activity, which was greater than T. mastichina. MIC and MLC values were similar for all the compounds tested. At MIC values of the essential oils, propidium iodide rapidly penetrated the majority of the yeast cells, indicating that the fungicidal effect resulted primarily from an extensive lesion of the cell membrane. Concentrations below the MIC values significantly inhibited germ tube formation. This study describes the potent antifungal activity of the essential oils of Thymus on Candida spp., warranting future therapeutical trials on mucocutaneous candidosis.

Antifungal Agents↗
PubMed2005

Patterns of variability in the diameter of lateral roots in the banana root system.

The relative importance of root system structure, plant carbon status and soil environment in the determination of lateral root diameter remains unclear, and was investigated in this study. Banana (Musa acuminata) plants were grown at various moderate levels of soil compaction in two distinct experiments, in a field experiment (FE) and in a glasshouse experiment (GE). Radiant flux density was 5 times lower in GE. The distribution of root diameter was measured for several root branching orders. Root diameters ranged between 0.09 and 0.52 mm for secondary roots and between 0.06 and 0.27 mm for tertiary roots. A relationship was found between the diameter of the parent bearing root and the median diameter of its laterals, which appears to be valid for a wide range of species. Mean lateral root diameter increased with distance to the base of the root and decreased with branching density [number of lateral roots per unit length of bearing root (cm(-1))]. Typical symptoms of low light availability were observed in GE. In this case, lateral root diameter variability was reduced. Although primary root growth was affected by soil compaction, no effects on lateral root diameter were observed.

Hot Temperature↗
PubMed1996

Evidence that the Piromyces gene family encoding endo-1,4-mannanases arose through gene duplication.

The sequences of two Piromyces cDNAs (manB and manC) encoding functional mannanases, defined as mannanase B (MANB) and mannanase C (MANC), revealed that both the cDNAs, and the encoded enzymes, exhibited extensive sequence identity with each other and with a previously described Piromyces mannanase. MANB and MANC, which belong to glycosyl hydrolase family 26, hydrolyse several forms of mannan but do not attack the other major plant structural polysaccharides. The data presented in this paper indicate that the Piromyces gene family encoding mannanases arose through gene duplication.

Amino Acid Sequence↗