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At least 433 records · Page 24Linked to original sources
PubMed2004

Functional analysis of the tandem-duplicated P450 genes SPS/BUS/CYP79F1 and CYP79F2 in glucosinolate biosynthesis and plant development by Ds transposition-generated double mutants.

A significant fraction (approximately 17%) of Arabidopsis genes are members of tandemly repeated families and pose a particular challenge for functional studies. We have used the Ac-Ds transposition system to generate single- and double-knockout mutants of two tandemly duplicated cytochrome P450 genes, SPS/BUS/CYP79F1 and CYP79F2. We have previously described the Arabidopsis supershoot mutants in CYP79F1 that exhibit massive overproliferation of shoots. Here we use a cytokinin-responsive reporter ARR5::uidA and an auxin-responsive reporter DR5::uidA in the sps/cyp79F1 mutant to show that increased levels of cytokinin, but not auxin, correlate well with the expression pattern of the SPS/CYP79F1 gene, supporting the involvement of this gene in cytokinin homeostasis. Further, we isolated Ds gene trap insertions in the CYP79F2 gene, and find these mutants to be defective mainly in the root system, consistent with a root-specific expression pattern. Finally, we generated double mutants in CYP79F1 and CYP79F2 using secondary transpositions, and demonstrate that the phenotypes are additive. Previous biochemical studies have suggested partially redundant functions for SPS/CYP79F1 and CYP79F2 in aliphatic glucosinolate synthesis. Our analysis shows that aliphatic glucosinolate biosynthesis is completely abolished in the double-knockout plants, providing genetic proof for the proposed biochemical functions of these genes. This study also provides further demonstration of how gluconisolate biosynthesis, regarded as secondary metabolism, is intricately linked with hormone homeostatis and hence with plant growth and development.

Arabidopsis↗
PubMed2004

SPIRAL1 encodes a plant-specific microtubule-localized protein required for directional control of rapidly expanding Arabidopsis cells.

Highly organized interphase cortical microtubule (MT) arrays are essential for anisotropic growth of plant cells, yet little is known about the molecular mechanisms that establish and maintain the order of these arrays. The Arabidopsis thaliana spiral1 (spr1) mutant shows right-handed helical growth in roots and etiolated hypocotyls. Characterization of the mutant phenotypes suggested that SPR1 may control anisotropic cell expansion through MT-dependent processes. SPR1 was identified by map-based cloning and found to encode a small protein with unknown function. Proteins homologous to SPR1 occur specifically and ubiquitously in plants. Genetic complementation with green fluorescent protein fusion proteins indicated that the SPR1 protein colocalizes with cortical MTs and that both MT localization and cell expansion control are conferred by the conserved N- and C-terminal regions. Strong SPR1 expression was found in tissues undergoing rapid cell elongation. Plants overexpressing SPR1 showed enhanced resistance to an MT drug and increased hypocotyl elongation. These observations suggest that SPR1 is a plant-specific MT-localized protein required for the maintenance of growth anisotropy in rapidly elongating cells.

Arabidopsis↗
PubMed2002

SINAT5 promotes ubiquitin-related degradation of NAC1 to attenuate auxin signals.

The plant hormone indole-3 acetic acid (IAA or auxin) controls many aspects of plant development, including the production of lateral roots. Ubiquitin-mediated proteolysis has a central role in this process. The genes AXR1 and TIR1 aid the assembly of an active SCF (Skp1/Cullin/F-box) complex that probably promotes degradation of the AUX/IAA transcriptional repressors in response to auxin. The transcription activator NAC1, a member of the NAM/CUC family of transcription factors, functions downstream of TIR1 to transduce the auxin signal for lateral root development. Here we show that SINAT5, an Arabidopsis homologue of the RING-finger Drosophila protein SINA, has ubiquitin protein ligase activity and can ubiquitinate NAC1. This activity is abolished by mutations in the RING motif of SINAT5. Overexpressing SINAT5 produces fewer lateral roots, whereas overexpression of a dominant-negative Cys49 --> Ser mutant of SINAT5 develops more lateral roots. These lateral root phenotypes correlate with the expression of NAC1 observed in vivo. Low expression of NAC1 in roots can be increased by treatment with a proteasome inhibitor, which indicates that SINAT5 targets NAC1 for ubiquitin-mediated proteolysis to downregulate auxin signals in plant cells.

Amino Acid Sequence↗
PubMed1988

All nod genes of Rhizobium meliloti are involved in alfalfa nodulation by exo mutants.

Nodulation of alfalfa by exoB mutants of Rhizobium meliloti occurred without root hair curling or infection thread formation. nod exoB double mutants had the same nodulation deficiency as single nod mutants. Therefore, all the known nod genes are involved in nodule induction by exoB mutants, which apparently occurs via intercellular invasion.

Chromosome Deletion↗
PubMed1977

The structure and composition of peripheral nerves and nerve roots in the Sprawling mouse.

Peripheral nerves and lumbar nerve roots of Sprawling, a neurological mutant mouse, were examined with light and electron microscopy. The peripheral nerves and the dorsal roots were thin and grey and were composed predominantly of small myelinated and unmyelinated axons. No evidence of axonal or myelin degeneration was found. Quantitative studies showed a marked reduction in the total number of myelinated axons with preponderance of those of 2-5 micron in diameter or less, most marked in the dorsal roots in which there was also an increase in the proportion of axons which were unmyelinated. In the ventral roots there was a deficiency in the contribution formed by myelinated axons of small calibre, probably indicating a deficiency of gamma fibres. Examination of the myelinated axons in nerves and roots showed a normal relationship between fibre size and internodal lengths and number of myelin lamellae. The findings suggest that the genetic defect in Sprawling is responsible for a failure of myelination of sensory axons. The deficiency of large sensory axons and of small motor axons can be correlated with the deficiency of muscle spindles.

Animals↗
PubMed1997

Hydrotropism: the current state of our knowledge.

The response of roots to a moisture gradient has been reexamined, and positive hydrotropism has been demonstrated in recent years. Agravitropic roots of a pea mutant have contributed to the studies on hydrotropism. The kinetics of hydrotropic curvature, interactions between hydrotropism and gravitropism, moisture gradients required for the induction of hydrotropism, the sensing site for moisture gradients, characteristics of hydrotropic signal and differential growth, and calcium involvement in signal transduction have been subjects of these studies. This review summarizes the current state of our knowledge on hydrotropism in roots.

Calcium↗
PubMed2003

Mutations in a gene for plastid ribosomal protein S6-like protein reveal a novel developmental process required for the correct organization of lateral root meristem in Arabidopsis.

Arabidopsis rfc3 mutants have previously been isolated with an altered fatty acid composition of membrane lipids. In this study, rfc3 was found to have a sucrose-conditional defect in the patterning of distal elements in the lateral root meristem. By utilizing this feature, a sucrose-sensitive process important for lateral root development was localized to the growing portion of rfc3 primary root. Because lateral root formation occurs at a later stage, this finding suggests the existence of an RFC3-dependent, non-primordium autonomous signal playing a role in the organization of lateral root meristem. Map-based cloning of RFC3 gene revealed that it encodes a plastid-localized ribosomal protein S6-like protein and provides a potential link between control of plastid gene expression and LR development.

Amino Acid Sequence↗
PubMed2002

Role of Pseudomonas putida indoleacetic acid in development of the host plant root system.

Many plant-associated bacteria synthesize the phytohormone indoleacetic acid (IAA). While IAA produced by phytopathogenic bacteria, mainly by the indoleacetamide pathway, has been implicated in the induction of plant tumors, it is not clear whether IAA synthesized by beneficial bacteria, usually via the indolepyruvic acid pathway, is involved in plant growth promotion. To determine whether bacterial IAA enhances root development in host plants, the ipdc gene that encodes indolepyruvate decarboxylase, a key enzyme in the indolepyruvic acid pathway, was isolated from the plant growth-promoting bacterium Pseudomonas putida GR12-2 and an IAA-deficient mutant constructed by insertional mutagenesis. The canola seedling primary roots from seeds treated with wild-type P. putida GR12-2 were on average 35 to 50% longer than the roots from seeds treated with the IAA-deficient mutant and the roots from uninoculated seeds. In addition, exposing mung bean cuttings to high levels of IAA by soaking them in a suspension of the wild-type strain stimulated the formation of many, very small, adventitious roots. Formation of fewer roots was stimulated by treatment with the IAA-deficient mutant. These results suggest that bacterial IAA plays a major role in the development of the host plant root system.

Amino Acid Sequence↗
PubMed2005

Proteomic analysis of different mutant genotypes of Arabidopsis led to the identification of 11 proteins correlating with adventitious root development.

A lack of competence to form adventitious roots by cuttings or explants in vitro occurs routinely and is an obstacle for the clonal propagation and rapid fixation of elite genotypes. Adventitious rooting is known to be a quantitative genetic trait. We performed a proteomic analysis of Arabidopsis (Arabidopsis thaliana) mutants affected in their ability to develop adventitious roots in order to identify associated molecular markers that could be used to select genotypes for their rooting ability and/or to get further insight into the molecular mechanisms controlling adventitious rooting. Comparison of two-dimensional gel electrophoresis protein profiles resulted in the identification of 11 proteins whose abundance could be either positively or negatively correlated with endogenous auxin content, the number of adventitious root primordia, and/or the number of mature adventitious roots. One protein was negatively correlated only to the number of root primordia and two were negatively correlated to the number of mature adventitious roots. Two putative chaperone proteins were positively correlated only to the number of primordia, and, interestingly, three auxin-inducible GH3-like proteins were positively correlated with the number of mature adventitious roots. The others were correlated with more than one parameter. The 11 proteins are predicted to be involved in different biological processes, including the regulation of auxin homeostasis and light-associated metabolic pathways. The results identify regulatory pathways associated with adventitious root formation and represent valuable markers that might be used for the future identification of genotypes with better rooting abilities.

Adaptation, Physiological↗
PubMed2005

A novel short-root gene encodes a glucosamine-6-phosphate acetyltransferase required for maintaining normal root cell shape in rice.

Glycosylation is a posttranslational modification occurring in many secreted and membrane-associated proteins in eukaryotes. It plays important roles in both physiological and pathological processes. Most of these protein modifications depend on UDP-N-acetylglucosamine. In this study, a T-DNA insertional rice (Oryza sativa) mutant exhibiting a temperature-sensitive defect in root elongation was isolated. Genetic and molecular analysis indicated that the mutated phenotype was caused by loss of function of a gene encoding a glucosamine-6-P acetyltransferase (designated OsGNA1), which is involved in de novo UDP-N-acetylglucosamine biosynthesis. The aberrant root morphology of the gna1 mutant includes shortening of roots, disruption of microtubules, and shrinkage of cells in the root elongation zone. Our observations support the idea that protein glycosylation plays a key role in cell metabolism, microtubule stabilization, and cell shape in rice roots.

Acetyltransferases↗
PubMed1978

Changes of the neuronal endoplasmic reticulum in the peripheral nervous system in mutant hamsters with hind leg paralysis and normal controls.

The fine structure of the spinal root and gasserian ganglia of the mutant hamster with hind leg paralysis and of normal controls was examined. Three types of whorl-like or lamellar alteration of the endoplasmic reticulum were encountered but these were also found in the normal control animals and are therefore probably not related to the paralysis of the mutants. These alterations of the endoplasmic reticulum were similar to or identical with those seen in a variety of other conditions and in other types of cells. In the hamster, however the three configurations could sometimes be seen within the same membranous accumulations and are probably related to one another in a developmental fashion.

Animals↗
PubMed2000

The Lotus japonicus LjSym4 gene is required for the successful symbiotic infection of root epidermal cells.

The role of the Lotus japonicus LjSym4 gene during the symbiotic interaction with Mesorhizobium loti and arbuscular mycorrhizal (AM) fungi was analyzed with two mutant alleles conferring phenotypes of different strength. Ljsym4-1 and Ljsym4-2 mutants do not form nodules with M. loti. Normal root hair curling and infection threads are not observed, while a nodC-dependent deformation of root hair tips indicates that nodulation factors are still perceived by Ljsym4 mutants. Fungal infection attempts on the mutants generally abort within the epidermis, but Ljsym4-1 mutants allow rare, successful, infection events, leading to delayed arbuscule formation. On roots of mutants homozygous for the Ljsym4-2 allele, arbuscule formation was never observed upon inoculation with either of the two AM fungi, Glomus intraradices or Gigaspora margarita. The strategy of epidermal penetration by G. margarita was identical for Ljsym4-2 mutants and the parental line, with appressoria, hyphae growing between two epidermal cells, penetration of epidermal cells through their anticlinal wall. These observations define a novel, genetically controlled step in AM colonization. Although rhizobia penetrate the tip of root hairs and AM fungi access an entry site near the base of epidermal cells, the LjSym4 gene is necessary for the appropriate response of this cell type to both microsymbionts. We propose that LjSym4 is required for the initiation or coordinated expression of the host plant cell's accommodation program, allowing the passage of both microsymbionts through the epidermis layer.

Alleles↗
PubMed2006

A novel plant-specific family gene, ROOT PRIMORDIUM DEFECTIVE 1, is required for the maintenance of active cell proliferation.

Hypocotyl segments of Arabidopsis (Arabidopsis thaliana) produce adventitious roots in response to exogenously supplied auxin. root primordium defective 1 (rpd1) is a temperature-sensitive mutant isolated on the basis of impairment in this phenomenon. This study describes further phenotypic analysis of the rpd1 mutant and isolation of the RPD1 gene. When adventitious root formation was induced from the rpd1 explants at the restrictive temperature, cell proliferation leading to root promordia formation was initiated at the same time as in wild-type explants. However, development of the root primordia was arrested thereafter in the mutant. Temperature-shift experiments indicated that RPD1 exerts its function before any visible sign of root primordium formation. The expression patterns of the auxin-responsive gene DR5:beta-glucuronidase and the cytodifferentiation marker gene SCARECROW suggest that the rpd1 mutation interferes with neither axis formation nor cellular patterning at the initial stage of root primordium development. Taken together with the effect of the rpd1 mutation on callus cell proliferation, these data imply a role for RPD1 in prearranging the maintenance of the active cell proliferation during root primordium development. Positional cloning of the RPD1 gene revealed that it encodes a member of a novel protein family specific to the plant kingdom. Disruption of the RPD1 gene by a T-DNA insertion caused embryogenesis arrest at the globular to transition stages. This phenotype is consistent with the hypothesized function of RPD1 in the maintenance of active cell proliferation.

Amino Acid Sequence↗
PubMed2004

The Arabidopsis transcription factor HY5 integrates light and hormone signaling pathways.

The role of the Arabidopsis transcription factor LONG HYPOCOTYL 5 (HY5) in promoting photomorphogenic development has been extensively characterized. Although the current model for HY5 action largely explains its role in this process, it does not adequately address the root phenotype observed in hy5 mutants. In our search for common mechanisms underlying all hy5 traits, we found that they are partly the result of an altered balance of signaling through the plant hormones auxin and cytokinin. hy5 mutants are resistant to cytokinin application, and double mutant analyses indicate that a decrease in auxin signaling moderates hy5 phenotypes. Microarray analyses and semiquantitative RT-PCR indicate that two negative regulators of auxin signaling, AUXIN RESISTANT 2 (AXR2)/INDOLE ACETIC ACID 7 (IAA7) and SOLITARY ROOT (SLR)/IAA14, are underexpressed in hy5 mutants. The promoters of these genes contain a putative HY5 binding site, and in line with this observation, HY5 can bind to the promoter of AXR2 in vitro. Increased AXR2 expression in a hy5 background partially rescues the elongated hypocotyl phenotype. In summary, it appears that auxin signaling is elevated in hy5 mutants because HY5 promotes the expression of negative regulators of auxin signaling, thereby linking hormone and light signaling pathways.

Arabidopsis↗
PubMed2000

PROCUSTE1 encodes a cellulose synthase required for normal cell elongation specifically in roots and dark-grown hypocotyls of Arabidopsis.

Mutants at the PROCUSTE1 (PRC1) locus show decreased cell elongation, specifically in roots and dark-grown hypocotyls. Cell elongation defects are correlated with a cellulose deficiency and the presence of gapped walls. Map-based cloning of PRC1 reveals that it encodes a member (CesA6) of the cellulose synthase catalytic subunit family, of which at least nine other members exist in Arabidopsis. Mutations in another family member, RSW1 (CesA1), cause similar cell wall defects in all cell types, including those in hypocotyls and roots, suggesting that cellulose synthesis in these organs requires the coordinated expression of at least two distinct cellulose synthase isoforms.

Alleles↗
PubMed2005

Sensitive detection and localization of hydroxyl radical production in cucumber roots and Arabidopsis seedlings by spin trapping electron paramagnetic resonance spectroscopy.

As reactive oxygen species are important for many fundamental biological processes in plants, specific and sensitive techniques for their detection in vivo are essential. In particular, the analysis of hydroxyl radical (OH*) formation in biological reactions has rarely been attempted. Here, it is shown that spin trapping electron paramagnetic resonance (EPR) spectroscopy allows the detection and quantitative estimation of OH* production in vivo in one single cucumber seedling root. It is possible to localize the OH* production site to the growth zone of the root by varying the position of the intact seedling inside the resonator cavity of the EPR spectrometer. Moreover, the demonstration of impaired OH* formation in the root of the Arabidopsis mutant rhd2 impaired in a superoxide-producing Nicotimamide adenine dinucleotide phosphate (NADPH) oxidase has been accomplished. Spin trapping EPR provides a valuable tool for analyzing the production of OH*in vivo with high resolution in small tissue samples.

Arabidopsis↗
PubMed1993

Bradyrhizobium japonicum TlpA, a novel membrane-anchored thioredoxin-like protein involved in the biogenesis of cytochrome aa3 and development of symbiosis.

We report the discovery of a bacterial gene, tlpA, that codes for a hitherto unknown type of thioredoxin-like protein. The gene was found in the course of studying a Tn5 insertion mutant of the soybean root nodule symbiont Bradyrhizobium japonicum. The TlpA protein shared up to 31% amino acid sequence identity with various eukaryotic and prokaryotic thioredoxins and protein disulfide isomerases, and possessed a characteristic active-site sequence, Trp-Cys-Val-Pro-Cys. In contrast to all members of the thioredoxin family known to date, TlpA was shown to be anchored to the cytoplasmic membrane by means of an N-terminal transmembrane domain, while the active site-containing part of the protein faced the periplasm. The tlpA mutant had a pleiotropic phenotype in that it was defective in the development of a nitrogen fixing endosymbiosis and exhibited a strongly decreased oxidase activity, as compared with the wild-type. Holocytochrome aa3 was spectroscopically undetectable in the mutant, whereas the apoprotein of subunit one (CoxA) of this oxidase was still synthesized and incorporated into the cytoplasmic membrane. Since cytochrome aa3 is not a prerequisite for the development of symbiosis, the results suggest that TlpA is involved in at least two independent cellular processes, one of which is an essential periplasmic step in the maturation of cytochrome aa3.

Alkaline Phosphatase↗
PubMed2004

An outer envelope membrane component of the plastid protein import apparatus plays an essential role in Arabidopsis.

Translocon at the outer envelope membrane of chloroplasts, 34 kDa (Toc34) is a GTP-binding component of the protein import apparatus within the outer envelope membrane of plastids. The Arabidopsis genome encodes two homologues of Toc34, designated atToc33 and atToc34. In this report, we describe the identification and characterization of two atToc34 knockout mutants, plastid protein import 3-1 (ppi3-1) and ppi3-2. Aerial tissues of the ppi3 mutants appeared similar to the wild type throughout development, and contained structurally normal chloroplasts that were able to efficiently import the Rubisco small subunit precursor (prSS) in vitro. The absence of an obvious ppi3 phenotype in green tissues presumably reflects the ability of atToc33 to substitute for atToc34 in the mutant, and the relatively high level of expression of the atTOC33 gene in these tissues. In the roots, where atTOC33 is expressed at a much lower level, significant growth defects were observed in both mutants: ppi3 roots were approximately 20-30% shorter than wild-type roots. Attempts to identify a double homozygote lacking atToc34 and atToc33 (by crossing the ppi3 mutants with ppi1, an atToc33 knockout mutant) were unsuccessful, indicating that the function provided by atToc33/atToc34 is essential during early development. Plants that were homozygous for ppi1 and heterozygous for ppi3 displayed a chlorotic phenotype much more severe than that of the ppi1 single mutant. Furthermore, the siliques of these plants contained approximately 25% aborted seeds, indicating that the double homozygous mutation is embryo lethal. The data demonstrate that atToc33/atToc34 performs a central and essential role during plastid protein import, and indicate that the atToc34 isoform is relatively more important for plastid biogenesis in roots.

Arabidopsis↗