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At least 415 records · Page 23Linked to original sources
PubMed2004

Release of the benzoxazinoids defense molecules during lateral- and crown root emergence in Zea mays.

We observed the release of the benzoxazinoids defense molecules on the surface of the primary root and the coleoptilar node in Zea mays during the emergence of lateral- and crown-roots, respectively. At later stages of crown root and lateral root development, benzoxazinoids around the emerged roots were no longer observed. Specific mutants revealed that the developmental status of the emerged roots was not important for the release of benzoxazinoids, but the breakage of the epidermis by emerging roots was. This is the first report of benzoxazinoid-release during normal development controlled by endogenous developmental programs. Release of benzoxazinoids around the emerging roots supports the idea that defense molecules accumulate at the site of root emergence in order to reduce pathogenic infections. We discuss possible explanations for the evolution of two different developmental mechanisms of root emergence.

Benzoxazines↗
PubMed1993

Differential expression of the rolA plant oncogene and its effect on tobacco development.

The rolA gene not only provokes the abnormal traits of wrinkled leaves, shortened internodes, and deficient root growth in tobacco, but also induction of roots in leaf disks in hormone-free medium. The rolA mRNA is most abundant in the stem of transgenic tobacco, accumulating at fivefold and 50-fold lower levels in the leaf and the root, respectively. Promoter deletion mutants were constructed and the rolA-induced abnormal traits were exploited to identify promoter regulatory regions. The removal of specific promoter domains provokes the appearance of new patterns of rolA transcripts in leaves, stems and roots. These new patterns are correlated with the disappearance of specific abnormal trait, thereby identifying three functional domains. Domain A includes a mosaic motif composed of a putative GT-2 binding site and DUE-NDE elements. This domain positively regulates rolA gene expression in the leaf and negatively regulates it in the stem and root. Domains B and C, which contain sequences homologous to the OCS enhancer and to ASF-1 binding sites, respectively, generally activate the rolA gene expression in all tissues. The possible function of these elements on the regulation of the rolA gene is discussed.

Base Sequence↗
PubMed1997

Bacterial genetic loci implicated in the Pseudomonas putida GR12-2R3--canola mutualism: identification of an exudate-inducible sugar transporter.

Pseudomonas putida GR12-2R3 promotes the emergence and growth of diverse plant species. Analyses of TnphoA insertion mutations are revealing bacterial characteristics pertinent to the plant-microbe interaction. Pseudomonas putida PG269 is a TnphoA insertion derivative of GR12-2R3 that expresses canola seed exudate-inducible alkaline phosphatase (PhoA) activity. It promoted the growth of canola roots, as well as strain GR12-2R3, and outgrew its parent when they were cocultured in the presence of canola roots or in liquid seed exudate medium. (In contrast, mutant PG126 failed to promote canola root growth and was outgrown by its parent strain.) The PhoA activity of strain PG269 was induced by glucosamine and other sugars; glucosamine inhibited the growth of strain GR12-2R3 and stimulated the growth of strain PG269. Strain PG269 contained two TnphoA insertions: seiA1::TnphoA and seiB1::TnphoA. Strain PG312, which contained only insertion seiA1::TnphoA, shared all aspects of the PG269 phenotype, except the ability to outcompete strain GR12-2R3 during coculture. Insertion seiA1::TnphoA interrupted an open reading frame related in sequence to members of the MalF family of sugar transporter subunits. The PhoA-inducing fraction of canola seed exudate was hydrophilic, low in molecular weight, and heat stable. It cochromatographed with basic amino acids and amino sugars, and was inactivated by strains GR12-2R3 and PG269. Gene seiA may encode a subunit of an ABC transporter with broad specificity for glucose and related sugars whose expression can be induced by exudate sugars.

Amino Acid Sequence↗
PubMed2004

Rhizobial nod gene-inducing activity in pea nodulation mutants: dissociation of nodulation and flavonoid response.

The root exudates of 24 pea (Pisum sativum L.) non-nodulating mutants, originating from cv. 'Finale', were tested for Rhizobium nodulation (nod) gene-inducing activity to reveal potential differences from the wild type. The interaction with flavonoid receptor NodD of R. leguminosarum bv. viciae strain 248 was monitored as the activity of the regulated operon nodABC fused to the reporter gene lacZ. In the uninoculated plants, the only decreased exudate activity was found in the line Risnod17 and ascribed to the impaired root growth in this line. Consequently, constitutive deficiency in the flavonoid nod gene inducers is not a cause of the asymbiotic phenotypes in the studied set. On the other hand, line Risnod5 had constitutively higher nod gene-inducing activity which might be responsible for its conditional nodulation and Fix(-) phenotype when the nodules are present. Monitoring of the response of wild-type plants to inoculation revealed an increase in nod gene-inducing activity (Ini response) starting first day after inoculation. The chosen mutant lines Risnod22 (putative locus sym9) and Risnod25 (putatively sym8) showed Ini as well indicating that the flavonoid burst can be mutationally dissociated from nodule initiation. On the other hand, absence of Ini in Risnod20 (assumed sym19) suggests branching of the signal transduction pathway downstream of this mutation and places it upstream of the two former mutations in the transduction of the bacterial Nod factor signal. More intense Ini response observed in the supernodulating mutant RisfixC, included in the study for its contrasting symbiotic phenotype, suggests common regulation of nodulation and Ini response via systemic shoot factor. The time shift in the exudation of isoflavonoid phytoalexin pisatin compared to Ini, its increased level in Risnod25 and lowered level in RisfixC are consistent with the regulatory role of plant defence in nodule initiation, which might be mediated directly by isoflavonoids as negative regulators.

Journal Article↗
PubMed1990

Either of two nod gene loci can complement the nodulation defect of a nod deletion mutant of Rhizobium leguminosarum bv viciae.

A deletion mutant of Rhizobium leguminosarum biovar viciae lacking the host-specific nodulation (nod) gene region (nodFEL nodMNT and nodO) but retaining the other nod genes (nodD nodABCIJ) was unable to nodulate peas or Vicia hirsuta, although it did induce root hair deformation. The mutant appeared to be blocked in its ability to induce infection threads and could be rescued for nodulation of V. hirsuta in mixed inoculation experiments with an exopolysaccharide deficient mutant (which is also Nod-). The nodulation deficiency of the deletion mutant strain could be partially restored by plasmids carrying the nodFE, nodFEL or nodFELMNT genes but not by nodLMN. Surprisingly, the mutant strain could also be complemented with a plasmid that did not carry any of the nodFELMNT genes but which did carry the nodO gene on a 30 kb cloned region of DNA. Using appropriate mutations it was established that nodO is essential for nodulation in the absence of nodFE. Thus, either of two independent nod gene regions can complement the deletion mutant for nodulation of V. hirsuta. Similar observations were made for pea nodulation except that nodL was required in addition to nodO for nodulation in the absence of the nodFE genes. These observations show that nodulation can occur via either of two pathways encoded by non-homologous genes.

Fabaceae↗
PubMed1991

Mutant of Arabidopsis deficient in xylem loading of phosphate.

A mutant of Arabidopsis thaliana deficient in the accumulation of inorganic phosphate has been isolated by screening directly for plants with altered quantities of total leaf phosphate. The mutant plants accumulate approximately 5% as much inorganic phosphate, and 24 to 44% as much total phosphate, as wild-type plants in aerial portions of the plant. Growth of the mutant is reduced, relative to wild type, and it exhibits other symptoms normally associated with phosphate deficiency. The phosphate deficiency is caused by a single nuclear recessive mutation at a locus designated pho1. The rate of phosphate uptake into the roots was similar between mutant and wild-type plants over a wide range of external phosphate concentrations. In contrast, when plants were grown in media containing 200 micromolar phosphate or less, phosphate transfer to the shoots of the mutant was reduced to 3 to 10% of the wild-type levels. The defect in phosphate transfer to the shoots could be overcome by providing higher levels of phosphate. Transfer of sulfate to the shoots was essentially normal in the mutant, indicating that the pho1 lesion was not a general defect in anion transport. Movement of phosphate through the xylem of the shoots was not impaired. The results suggest that the mutant is deficient in activity of a protein required to load phosphate into the xylem.

Journal Article↗
PubMed2003

Control of growth cone motility and morphology by LIM kinase and Slingshot via phosphorylation and dephosphorylation of cofilin.

Growth cone motility and morphology are based on actin-filament dynamics. Cofilin plays an essential role for the rapid turnover of actin filaments by severing and depolymerizing them. The activity of cofilin is repressed by phosphorylation at Ser3 by LIM kinase (LIMK, in which LIM is an acronym of the three gene products Lin-11, Isl-1, and Mec-3) and is reactivated by dephosphorylation by phosphatases, termed Slingshot (SSH). We investigated the roles of cofilin, LIMK, and SSH in the growth cone motility and morphology and neurite extension by expressing fluorescence protein-labeled cofilin, LIMK1, SSH1, or their mutants in chick dorsal root ganglion (DRG) neurons and then monitoring live images of growth cones by time-lapse video fluorescence microscopy. The expression of LIMK1 remarkably repressed growth cone motility and neurite extension, whereas the expression of SSH1 or a nonphosphorylatable S3A mutant of cofilin enhanced these events. The fan-like shape of growth cones was disorganized by the expression of any of these proteins. The repressive effects on growth cone behavior by LIMK1 expression were significantly rescued by the coexpression of S3A-cofilin or SSH1. These findings suggest that LIMK1 and SSH1 play critical roles in controlling growth cone motility and morphology and neurite extension by regulating the activity of cofilin and may be involved in signaling pathways that regulate stimulus-induced growth cone guidance. Using various mutants of cofilin, we also obtained evidence that the actin-filament-severing activity of cofilin is critical for growth cone motility and neurite extension.

Actin Cytoskeleton↗
PubMed2003

Hydrotropism interacts with gravitropism by degrading amyloplasts in seedling roots of Arabidopsis and radish.

In response to a moisture gradient, roots exhibit hydrotropism to control the orientation of their growth. To exhibit hydrotropism, however, they must overcome the gravitropism that is dominant on Earth. We found that moisture gradient or water stress caused immediate degradation of the starch anchors, amyloplasts, in root columella cells of Arabidopsis and radish (Raphanus sativus). Namely, development of hydrotropic response was accompanied by a simultaneous reduction in starch content in columella cells. Rapid degradation of amyloplasts in columella cells also occurred in the water-stressed roots with sorbitol or mannitol. Both hydrotropically stimulated and water-stressed roots showed a reduced responsiveness to gravity. Roots of a starchless mutant, pgm1-1, showed an enhanced hydrotropism compared with that of the wild type. These results suggest that the reduced responsiveness to gravity is, at least in part, attributable to the degradation of amyloplasts in columella cells. Thus, the reduction in gravitropism allows the roots to exhibit hydrotropism.

Arabidopsis↗
PubMed1988

Induction of pathogenic-like responses in the legume Macroptilium atropurpureum by a transposon-induced mutant of the fast-growing, broad-host-range Rhizobium strain NGR234.

Mutant strain ANU2861, a transposon Tn5 mutant of the fast-growing, broad-host-range Rhizobium strain ANU280 (NGR234 Smr Rfr) overproduces polysaccharide, is an ade auxotroph, and induces poorly developed nodules on Leucaena leucocephala and Lablab purpureus (H.C. Chen, M. Batley, J.W. Redmond, and B.G. Rolfe, J. Plant Physiol. 120:331-349, 1985). Strain ANU2861 cannot form nodules on Macroptilium atropurpureum Urb. (siratro) or on Desmodium intortum and D. uncinatum and the nonlegume Parasponia. The parent strain, ANU280, effectively nodulates all these legume species except Parasponia, on which it forms ineffective nodules. Ultrastructural examination of infection sites on the legume siratro showed that mutant strain ANU2861 caused root hair curling (Hac+ phenotype), some cortical cell division (Noi+), but no infection threads (Inf-). Localized cellular responses, known to occur in phytopathological interactions, were observed in electron micrographs of the epidermal tissue at or near the infection zone after inoculation with strain ANU2861 but not the wild-type parental strain. These include (i) the rapid (within 20 h) accumulation of osmiophilic droplets attached to membranes at potential sites of strain ANU2861 penetration and (after 48 h) in the epidermal cells in the immediate region of the curled root hairs, and (ii) localized cell death of the epidermal cells. In addition, strain ANU2861 can initiate a systemic response in split-root siratro plants which prevents the successful nodulation of strain ANU280. A 6.3-kilobase fragment of wild-type genomic DNA, which includes the site of Tn5 insertion in strain ANU2861, was cloned and introduced to strain ANU2861. All the phenotypic defects of the mutant strain were corrected by the introduction of this DNA fragment. This indicates that the original Tn5 insertion is responsible for the phenotype.

Cloning, Molecular↗
PubMed2004

Analysis of Pseudomonas fluorescens F113 genes implicated in flagellar filament synthesis and their role in competitive root colonization.

The ability of plant-associated micro-organisms to colonize and compete in the rhizosphere is specially relevant for the biotechnological application of micro-organisms as inoculants. Pseudomonads are one of the best root colonizers and they are widely used in plant-pathogen biocontrol and in soil bioremediation. This study analyses the motility mechanism of the well-known biocontrol strain Pseudomonas fluorescens F113. A 6.5 kb region involved in the flagellar filament synthesis, containing the fliC, flaG, fliD, fliS, fliT and fleQ genes and part of the fleS gene, was sequenced and mutants in this region were made. Several non-motile mutants affected in the fliC, fliS and fleQ genes, and a fliT mutant with reduced motility properties, were obtained. These mutants were completely displaced from the root tip when competing with the wild-type F113 strain, indicating that the wild-type motility properties are necessary for competitive root colonization. A mutant affected in the flaG gene had longer flagella, but the same motility and colonization properties as the wild-type. However, in rich medium or in the absence of iron limitation, it showed a higher motility, suggesting the possibility of improving competitive root colonization by manipulating the motility processes.

Bacterial Proteins↗
PubMed1996

Azorhizobium caulinodans uses both cytochrome bd (quinol) and cytochrome cbb3 (cytochrome c) terminal oxidases for symbiotic N2 fixation.

Azorhizobium caulinodans employs both cytochrome bd (cytbd; quinol oxidase) and cytcbb3 (cytc oxidase) as terminal oxidases in environments with very low O2 concentrations. To investigate physiological roles of these two terminal oxidases both in microaerobic culture and in symbiosis, knockout mutants were constructed. As evidenced by visible absorbance spectra taken from mutant bacteria carrying perfect gene replacements, both the cytbd- and cytcbb3- mutations were null alleles. In aerobic culture under 2% O2 atmosphere, Azorhizobium cytbd- and cytcbb3- single mutants both fixed N2 at 70 to 90% of wild-type rates; in root nodule symbiosis, both single mutants fixed N2 at 50% of wild-type rates. In contrast, Azorhizobium cytbd- cytcbb3-double mutants, which carry both null alleles, completely lacked symbiotic N2 fixation activity. Therefore, both Azorhizobium cytbd and cytcbb3 oxidases drive respiration in environments with nanomolar O2 concentrations during symbiotic N2 fixation. In culture under a 2% O2 atmosphere, Azorhizobium cytbd- cytcbb3- double mutants fixed N2 at 70% of wild-type rates, presumably reflecting cytaa3 and cytbo (and other) terminal oxidase activities. In microaerobic continuous cultures in rich medium, Azorhizobium cytbd- and cytcbb3- single mutants were compared for their ability to deplete a limiting-O2 sparge; cytbd oxidase activity maintained dissolved O2 at 3.6 microM steady state, whereas cytcbb3 oxidase activity depleted O2 to submicromolar levels. Growth rates reflected this difference; cytcbb3 oxidase activity disproportionately supported microaerobic growth. Paradoxically, in O2 limited continuous culture, Azorhizobium cytbd oxidase is inactive below 3.6 microM dissolved O2 whereas in Sesbania rostrata symbiotic nodules, in which physiological, dissolved O2 is maintained at 10 to 20 nM, both Azorhizobium cytbd and cytcbb3 seem to contribute equally as respiratory terminal oxidases.

Aerobiosis↗
PubMed2026

Maize terpene synthase 8 (ZmTPS8) produces a blend of sesquiterpenes and contributes to defense against pests and pathogens.

Maize (Zea mays) produces terpenoid-based chemical defenses through a large family of terpene synthases, but the contributions of individual enzymes to specific compounds and stress resistance remain difficult to predict. Maize terpene synthase 8 (ZmTPS8) produces multiple sesquiterpenes in heterologous systems, but its in planta function remains unknown. We integrated a metabolite genome-wide association study (mGWAS), CRISPR/Cas9 generated tps8 loss-of-function mutants, metabolite profiling, and biotic stress assays to define ZmTPS8's role in terpene synthesis and biotic stress responses. The mGWAS identified ZmTPS8 as the primary locus associated with herbivore-induced emission of the sesquiterpene volatile germacrene D. Consistently, ZmTPS8 expression was induced by foliar and root herbivory, and tps8 mutants exhibited reduced emission of germacrene D, α-copaene, and δ-cadinene during Spodoptera frugiperda feeding. Loss of ZmTPS8 increased S. frugiperda larval growth but did not affect the belowground herbivore Diabrotica virgifera virgifera. ZmTPS8 also contributed to resistance against sugarcane mosaic virus, and the fungal pathogen Fusarium verticillioides, affecting terpenoid profiles, global metabolism, and fungal toxin production, but had no impact on Cochliobolus heterostrophus or Pythium spp. susceptibility. Together, these results demonstrate that ZmTPS8 contributes to maize defense in a threat-dependent manner, shaping volatile emissions and defense outcomes.

Zea mays↗
PubMed2004

Root cap specific expression of an endo-beta-1,4-D-glucanase (cellulase): a new marker to study root development in Arabidopsis.

The sloughing of root cap cells from the root tip is important because it assists the growing root in penetrating the soil. Using a promoter-reporter (GUS) and RT-PCR analysis, we identified an endo-beta-1,4-glucanase (AtCel5) of Arabidopsis thaliana that is expressed exclusively in root cap cells of both primary and secondary roots. Expression is inhibited by high concentrations of IAA, both exogenous and internal, as well as by ABA. AtCel5 expression begins once the mature tissue pattern is established and continues for 3 weeks. GUS staining is observed in both root cap cells that are still attached and cells that have already been shed. Using AtCel5-GUS as a marker, we observed that the root cap cells begin to separate at the sides of the tip while the cells of the central region of the tip separate last. Separation involves sequential tiers of intact cells that separate from the periphery of the root tip. A homozygous T-DNA insertion mutant that does not express AtCel5 forms the root cap and sheds root cap cells but sloughing is less efficient compared to wild type. The reduction in sloughing in the mutant does not affect the overall growth performance of the plant in loose media. The modest effect of abolishing AtCel5 expression suggests that there are multiple redundant genes regulating the process of sloughing of the root cap, including AtCel3/At1g71380, the paralog of the AtCel5 gene that is also expressed in the root cap cells. Thus, these two endo-1,4-beta-D-glucanases may have a role in the sloughing of border cells from the root tip. We propose that AtCel5, provides a new molecular marker to further analyze the process of root cap cell separation and a root cap specific promoter for targeting to the environment genes with beneficial properties for plant growth.

Abscisic Acid↗
PubMed1995

Nerve growth factor-regulated properties of sensory neurones in Oct-2 null mutant mice.

The POU-domain transcription factor Oct-2 is expressed in both B lymphocytes and sensory neurones, where its expression is regulated by nerve growth factor (NGF). In order to define a possible role for Oct-2 in neurotrophin signalling, we examined the expression of an NGF-regulated channel (capsaicin-evoked ion fluxes), neuropeptides (substance P, calcitonin gene-related peptide), structural proteins (neurofilaments and peripherin) and receptors (trks) in dorsal root ganglion neurones derived from perinatal transgenic mice containing a defective Oct-2 structural gene. Northern blots show that central nervous tissue contains a larger than normal (> 10 kb) mRNA transcript corresponding in size to an Oct-2 transcript encoding a defective protein. PCR analysis shows the absence of normal Oct-2 transcripts in dorsal root ganglia. In null mutants, capsaicin sensitivity, and neuropeptide and cytoskeletal protein expression were unaffected by the loss of Oct-2 expression. The number of sensory neurones and the gross morphology of CNS tissues that normally express high levels of Oct-2 were also examined and found to be normal in the null mutant. Heterozygous animals show normal thresholds of sensitivity to noxious heat and normal inflammatory responses. Oct-2 does not therefore play an essential role in the NGF responsiveness of sensory neurones in these animals.

Animals↗
PubMed2002

The Arabidopsis mutant cev1 links cell wall signaling to jasmonate and ethylene responses.

Biotic and abiotic stresses stimulate the synthesis of jasmonates and ethylene, which, in turn, induce the expression of genes involved in stress response and enhance defense responses. The cev1 mutant has constitutive expression of stress response genes and has enhanced resistance to fungal pathogens. Here, we show that cev1 plants have increased production of jasmonate and ethylene and that its phenotype is suppressed by mutations that interrupt jasmonate and ethylene signaling. Genetic mapping, complementation analysis, and sequence analysis revealed that CEV1 is the cellulose synthase CeSA3. CEV1 was expressed predominantly in root tissues, and cev1 roots contained less cellulose than wild-type roots. Significantly, the cev1 mutant phenotype could be reproduced by treating wild-type plants with cellulose biosynthesis inhibitors, and the cellulose synthase mutant rsw1 also had constitutive expression of VSP. We propose that the cell wall can signal stress responses in plants.

Arabidopsis↗
PubMed2002

Genetic counseling in Leber hereditary optic neuropathy (LHON).

PURPOSE: To demonstrate the importance of mitochondrial DNA (mtDNA) analysis in the diagnosis of Leber hereditary optic neuropathy (LHON) and illustrate the difficulties in genetic counseling of the disease. PARTICIPANTS AND METHODS: Ophthalmological and molecular genetic study of one affected and three unaffected members from a family with heteroplasmic ND1/3460 mtDNA mutation associated with LHON. RESULTS: The proband had variable amounts of mutant mtDNA in all his tissues studied, ranging from 58% in blood to 92% in subcutis. The mother had an extremely low amount of mutant mtDNA in her tissues, except for hair roots, which contained only normal mtDNA. No mutant mtDNA could be detected in the proband's unaffected sister and maternal aunt. CONCLUSIONS: Despite her minimal mutation load, the mother of the proband has still transmitted a considerable amount of mutant mtDNA to her son, who is severely affected. Although proband's unaffected sister and maternal aunt had no mutant mtDNA, a theoretical risk that they may transmit the disease to their offspring cannot be excluded.

Adult↗