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At least 55 records · Page 3Linked to original sources
PubMed1997

A root-specific iron-regulated gene of tomato encodes a lysyl-tRNA-synthetase-like protein.

The tomato mutant chloronerva exhibits a defect in iron-uptake regulation. Despite high apoplastic and symplastic iron concentrations, the mutant shows characteristic symptoms of iron deficiency. Using a subtractive-hybridisation approach, we have screened for cDNA clones specific for genes with altered expression in wild-type versus mutant root tissue. Based on this clone collection, we have isolated and characterised a 2075-bp full-length cDNA encoding a lysyl-tRNA-synthetase-like protein. The corresponding gene is localised as a single copy on chromosome 10. Its expression is strongly induced by changes in the iron status of the plant. This iron-dependent regulation is superimposed upon a strict root specificity of gene expression. Possible functions of the gene product other than in protein biosynthesis will be discussed.

Amino Acid Sequence↗
PubMed2005

MDR-like ABC transporter AtPGP4 is involved in auxin-mediated lateral root and root hair development.

Previous data have suggested an involvement of MDR/PGP-like ABC transporters in transport of the plant hormone auxin and, recently, AtPGP1 has been demonstrated to catalyze the primary active export of auxin. Here we show that related isoform AtPGP4 is expressed predominantly during early root development. AtPGP4 loss-of-function plants reveal enhanced lateral root initiation and root hair lengths both known to be under the control of auxin. Further, atpgp4 plants show altered sensitivities toward auxin and the auxin transport inhibitor, NPA. Finally, mutant roots reveal elevated free auxin levels and reduced auxin transport capacities. These results together with yeast growth assays suggest a direct involvement of AtPGP4 in auxin transport processes controlling lateral root and root hair development.

ATP-Binding Cassette Transporters↗
PubMed1984

Mechanisms of cytoplasmic pH regulation in hypoxic maize root tips and its role in survival under hypoxia.

We show that a transient lactic fermentation provides the signal triggering ethanol production in hypoxic maize root tips. The signal is cytoplasmic pH. This interaction between lactic and ethanolic fermentation permits tight cytoplasmic pH regulation during hypoxia--cytoplasmic pH remaining near neutrality for several hours. Mutant roots unable to synthesize ethanol can neither regulate cytoplasmic pH nor maintain ATP levels during extended periods of hypoxia and, like vertebrate tissues, are less tolerant of hypoxia than normal maize. This indicates that cytoplasmic pH regulation is an important factor in survival under hypoxia.

Cytoplasm↗
PubMed1982

Structural studies of alfalfa roots infected with nodulation mutants of Rhizobium meliloti.

Alfalfa roots infected with four nodulation defective (Nod-) mutants of Rhizobium meliloti which were generated by transposon Tn5 mutagenesis were examined by light and electron microscopy. In one class of Nod- mutants, which we can nonreactive, the bacteria did not induce root hair curling or penetrate host cells. In a second class of Nod- mutants, which we call reactive, the bacteria induced some root hair curling and entered root epidermal cells, although no infection threads were formed. In addition, reactive Nod- mutants induced extensive root hair proliferation and hypertrophied roots. This study presents the details of the phenotype of the association between each mutant strain and alfalfa roots.

Medicago sativa↗
PubMed1987

Transposon Mutants of Bradyrhizobium japonicum Altered in Attachment to Host Roots.

Transposon mutants of Bradyrhizobium japonicum 110 ARS were produced and screened for changes in attachment ability. Mutant CFK4 produced twice as many piliated cells, attached in 2.5-fold-higher numbers to soybean root segments, and colonized roots in about 2-fold-higher numbers than did the parental strain, 110 ARS. Mutants CFK35 and CFK38 were reduced in their attachment about 2-fold and 3.5-fold, respectively. This corresponded to reductions in piliated cells in their populations, reduced reaction with anti-pilus antiserum, and reduced hydrophobic attachment. Mutants CFK4 and CFK38 nodulated soybeans at about the same level as the parent strain, but CFK35 induced only pseudonodules. Two-dimensional gel analyses of the proteins from the mutants showed relatively few changes in proteins.

Journal Article↗
PubMed1995

Plant development: pulled up by the roots.

Recent advances in the study of root development in Arabidopsis have begun to yield mechanistic insights into the processes that underpin morphogenesis, pattern formation and cell differentiation in plants. The most exciting feature of these advances is that, as a consequence of the simple and largely invariant cellular architecture of the root, the processes can be studied at a cellular level. Nevertheless, it is clear that although the cell lineages of the root are relatively invariant, we have no evidence that lineage per se is an important regulator of development. Instead, all the evidence indicates that the positional regulation of inductive cues is of primary importance. The availability of new root mutants is alerting us to the complexity of the contribution of cell size and cell expansion to plant development.

Arabidopsis↗
PubMed2006

Vectorial information for Arabidopsis planar polarity is mediated by combined AUX1, EIN2, and GNOM activity.

Cell polarity is commonly coordinated within the plane of a single tissue layer (planar polarity), and hair positioning has been exploited as a simple marker for planar polarization of animal epithelia . The root epidermis of the plant Arabidopsis similarly reveals planar polarity of hair localization close to root tip-oriented (basal) ends of hair-forming cells . Hair position is directed toward a concentration maximum of the hormone auxin in the root tip , but mechanisms driving this plant-specific planar polarity remain elusive. Here, we report that combinatorial action of the auxin influx carrier AUX1, ETHYLENE-INSENSITIVE2 (EIN2) , and GNOM genes mediates the vector for coordinate hair positioning. In aux1;ein2;gnom eb triple mutant roots, hairs display axial (apical or basal) instead of coordinate polar (basal) position, and recruitment of Rho-of-Plant (ROP) GTPases to the hair initiation site reveals the same polar-to-axial switch. The auxin concentration gradient is virtually abolished in aux1;ein2;gnom eb roots, where locally applied auxin can coordinate hair positioning. Moreover, auxin overproduction in sectors of wild-type roots enhances planar ROP and hair polarity over long and short distances. Hence, auxin may provide vectorial information for planar polarity that requires combinatorial AUX1, EIN2, and GNOM activity upstream of ROP positioning.

Arabidopsis↗
PubMed1992

A Single Genetic Locus, Ckr1, Defines Arabidopsis Mutants in which Root Growth Is Resistant to Low Concentrations of Cytokinin.

Arabidopsis mutants resistant to cytokinin (benzyladenine [BA]) have been isolated with the intent to find plants defective in cytokinin perception or response. At low concentrations, BA produces a "cytokinin root syndrome" in which primary root elongation is inhibited, but root hair elongation is stimulated. Five independent mutants that did not express this syndrome in the presence of BA were selected. All five mutants were recessive, and crosses between them indicated that they were in the same complementation group. The genetic locus represented by these mutations has been designated ckr1 and mapped to chromosome 5.

Journal Article↗
PubMed2006

Analysis of the DECREASED APICAL DOMINANCE genes of petunia in the control of axillary branching.

Control of branch development is a major determinant of architecture in plants. Branching in petunia (Petunia hybrida) is controlled by the DECREASED APICAL DOMINANCE (DAD) genes. Gene functions were investigated by plant grafting, morphology studies, double-mutant characterization, and gene expression analysis. Both dad1-1 and dad3 increased branching mutants can be reverted to a near-wild-type phenotype by grafting to a wild-type or a dad2 mutant root stock, indicating that both genes affect the production of a graft-transmissible substance that controls branching. Expression of the DAD1 gene in the stems of grafted plants, detected by quantitative reverse transcription-polymerase chain reaction correlates with the branching phenotype of the plants. The dad2-1 mutant cannot be reverted by grafting, indicating that this gene acts predominantly in the shoot of the plant. Double-mutant analysis indicates that the DAD2 gene acts in the same pathway as the DAD1 and DAD3 genes because the dad1-1dad2-1 and dad2-1dad3 double mutants are indistinguishable from the dad2-1 mutant. However, the dad1-1dad3 double mutant has an additive phenotype, with decreased height of the plants, delayed flowering, and reduced germination rates compared to the single mutants. This result, together with the observation that the dad1-1 and dad3 mutants cannot be reverted by grafting to each other, suggests that the DAD1 and DAD3 genes act in the same pathway, but not in a simple stepwise fashion.

Gene Expression Regulation, Plant↗
PubMed1997

A pleiotropic Arabidopsis thaliana mutant with inverted root chirality.

Circumnutation is an oscillating movement of a growing plant organ that is believed to result from an endogenous rhythmic process intrinsic to growth. Circumnutating organs, as they extend, describe a helical trace. In Arabidopsis thaliana (L.) Heynh. circumnutation is particularly evident in primary roots and occurs, as in most plants, in a right-handed direction when viewed from above in the direction of the growing tips. We have discovered a pleiotropic mutant of Arabidopsis with left-handed root circumnutation. Major abnormalities of the mutant are: (i) a reduced size of all organs, mainly due to a defect in cell elongation or expansion; (ii) a zigzagging pattern of stem pith cells, reminiscent of the "erectoides" phenotype of the lk mutant of Pisum; (iii) roots of the mutant are gravitropic but as they grow, they form tight, left-handed coils. Genetically, the mutant depends on the presence of two independent monogenic recessive factors acting additively. The mutant alleles of both factors alter the growth of the aerial organs in a similar manner but differ at the root level: one mainly produces non-circumnutating roots, the other changes the direction of circumnutation from right to left hand.

Arabidopsis↗
PubMed2001

[Identification of a gene, included in control of root system development in Arabidopsis thaliana].

Genetic and molecular genetic analysis of a lethal root mutant of Arabidopsis thaliana was carried out. The mutant was obtained from a collection created earlier by means of insertion mutagenesis. The mutation was found to be recessive. It was caused by an insertion of the T region of vector pLD3 used for transformation of germinating seeds when creating the collection of insertion mutants. A 118-bp DNA fragment flanking the left border of the insertion was isolated using the TAIL PCR technique, and its nucleotide sequence was determined. Computer analysis of this DNA region demonstrated that it was located in exon 32 of the YUP8HI2R.44 gene in chromosome 1.

Arabidopsis↗
PubMed1994

Cell biology of plant gravity sensing.

The debate about whether gravity sensing relies upon statoliths (amyloplasts that sediment) has intensified with recent findings of gravitropism in starchless mutants and of claims of hydrostatic gravity sensing. Starch and significant plastid sedimentation are not necessary for reduced sensing in mutant roots, but plastids might function here if there were a specialized receptor for plastid mass e.g. in the ER. Alternatively, components in addition to amyloplasts might provide mass for sensing. The nucleus is dense and its position is regulated, but no direct data exist for its role in sensing. If the weight of the protoplast functioned in sensing, why would there be specific cytological specializations favoring sedimentation rather than cell mass? Gravity has multiple effects on plants in addition to gravitropism. There may be more than one mechanism of gravity sensing.

Cell Nucleus↗
PubMed2006

A Ca(2)+ signaling pathway regulates a K(+) channel for low-K response in Arabidopsis.

Nutrient sensing is critical for plant adaptation to the environment. Because of extensive farming and erosion, low content of mineral nutrients such as potassium (K(+)) in soils becomes a limiting factor for plant growth. In response to low-K conditions, plants enhance their capability of K(+) uptake through an unknown signaling mechanism. Here we report the identification of a Ca(2+)-dependent pathway for low-K response in Arabidopsis. We are not aware of any other example of a molecular pathway for a nutrient response in plants. Earlier genetic analyses revealed three genes encoding two Ca(2+) sensors (CBL1 and CBL9) and their target protein kinase (CIPK23) to be critical for plant growth on low-K media and for stomatal regulation, indicating that these calcium signaling components participate in the low-K response and turgor regulation. In this study, we show that the protein kinase CIPK23 interacted with, and phosphorylated, a voltage-gated inward K(+) channel (AKT1) required for K(+) acquisition in Arabidopsis. In the Xenopus oocyte system, our studies showed that interacting calcium sensors (CBL1 and CBL9) together with target kinase CIPK23, but not either component alone, activated the AKT1 channel in a Ca(2+)-dependent manner, connecting the Ca(2+) signal to enhanced K(+) uptake through activation of a K(+) channel. Disruption of both CBL1 and CBL9 or CIPK23 gene in Arabidopsis reduced the AKT1 activity in the mutant roots, confirming that the Ca(2+)-CBL-CIPK pathway functions to orchestrate transporting activities in planta according to external K(+) availability.

Animals↗
PubMed1992

Urease-null and hydrogenase-null phenotypes of a phylloplane bacterium reveal altered nickel metabolism in two soybean mutants.

Mutation at either of two genetic loci (Eu2 or Eu3) in soybean (Glycine max [L.] Merr.) results in a pleiotropic elimination of the activity of both major urease isozymes. Surprisingly, the phenotype of a phylloplane bacterium, Methylobacterium mesophilicum, living on the leaves of eu2/eu2 or eu3-e1/eu3-e1 mutants is also affected by these plant mutations. The bacteria isolated from leaves of these soybean mutants have transient urease- and hydrogenase-deficient phenotypes that can be corrected by the addition of nickel to free-living cultures. The same bacterium growing on wild-type soybeans or on urease mutants eu1-sun/eu1-sun or eu4/eu4, each deficient in only one urease isozyme, are urease-positive. These results suggest that the bacterium living on the eu2/eu2 or eu3-e1/eu3-e1 mutant is unable to produce an active urease or hydrogenase because it is effectively starved for nickel. We infer that mutations at Eu2 or Eu3 result in defects in nickel metabolism but not in Ni(2+) uptake or transport, because eu2/eu2 and eu3-e1/eu3-e1 mutants exhibit normal uptake of (63)NiCl(2). Moreover, wild-type plants grafted on mutant rootstocks produce seeds with fully active urease, indicating unimpeded transport of nickel through mutant roots and stems.

Journal Article↗
PubMed2004

Growth regulators and the control of nucleotide sugar flux.

A small number of plant growth regulators are involved in the control of cell expansion. Despite knowledge of some of their signal transduction cascades, surprisingly little is known of how basic cell expansion-related processes, such as cell wall biosynthesis, are affected during growth. The Arabidopsis (Arabidopsis thaliana) mutant root hair defective1 (rhd1) lacks a functional UDP-glucose 4-epimerase gene, UGE4, which is involved in channeling UDP-D-galactose (UDP-D-Gal) into cell wall polymers. Here, we use rhd1 as a genetic model to analyze the physiological and genetic controls of nucleotide sugar flux. We find that ethylene specifically suppresses all visible aspects of the rhd1 phenotype. The ethylene-triggered suppression of rhd1 is negatively regulated by CONSTITUTIVE TRIPLE RESPONSE1 and requires the function of the wild-type genes ETHYLENE INSENSITIVE2 (EIN2), EIN4, AUXIN-RESISTENT1, and ETHYLENE-INSENSITIVE ROOT1 but does not depend on the activity of wild-type ETHYLENE RECEPTOR1 or EIN3 genes, highlighting the nonlinearity of ethylene signal transduction. Ethylene does not induce the expression of alternative UGE genes but, instead, suppresses the expression of two isoforms, UGE1 and UGE3, in a tissue-specific manner. Ethylene restores the biosynthesis of galactose-containing xyloglucan and arabinosylated galactan cell wall polymers in rhd1 back to wild-type levels. However, the dependence on UGE4 of pectic (1-->4)-beta-D-galactan and glucuronosyl-modified AGP biosynthesis is exacerbated. Our data suggest that ethylene and auxin together participate in the flux control of UDP-D-Gal into cell wall polymers and that the genetic control of this process is qualitatively distinct from previously described responses to ethylene.

Arabidopsis↗
PubMed2002

The growth defect of lrt1, a maize mutant lacking lateral roots, can be complemented by symbiotic fungi or high phosphate nutrition.

The growth of three maize (Zea mays L.) mutants, each impaired in the formation of one individual element of its root system, was compared under "natural" limiting phosphate conditions (0.1 mM). Mutant plants exhibiting a reduction in root hairs (rth3-1) or a depletion of crown and brace roots (rtcs) grew as well as the corresponding wild-type plants. However, mutant plants lacking lateral roots (lrt1) showed a strong reduction in plant growth. The growth defect of lrt1 was overcome when it was grown in association with an arbuscular mycorrhizal fungus, Glomus mosseae. Establishment of symbiosis was associated with the occurrence of a new type of lateral root. These new lateral roots were stunted and highly branched, giving rise to a bush-like structure. Supply of high phosphate (1 microM) ameliorated the growth of lrt1 plants too, but less efficiently than the symbiosis did. Hence, arbuscular mycorrhizal fungi as well as phosphate functionally complemented the lrt1 mutation.

Fungi↗
PubMed1987

The Isolation and Partial Characterization of the Lipopolysaccharides from Several Rhizobium trifolii Mutants Affected in Root Hair Infection.

The lipopolysaccharides (LPSs) from Rhizobium trifolii ANU843 and several transposon (Tn5) symbiotic mutants derived from ANU843 were isolated and partially characterized. The mutant strains are unable to induce normal root hair curling (Hac- phenotype) or nodulation (Nod-phenotype) in clover plants. The LPSs from the parent and mutants are very similar in composition. Analysis by PAGE shows that the LPSs consist of higher and lower molecular weight forms. The higher molecular weight form of the LPSs exists in several aggregation states when PAGE is done in 0.1% SDS but collapses into a single band when PAGE is done in 0.5% SDS. Mild acid hydrolysis of all the LPSs releases two polysaccharides, PS1 and PS2. Immunoblots of the PAGE gels and enzyme linked immunosorbant assay inhibition assays show that the PS1 fractions contain the immunodominant sites of the LPSs and that these sites are present in the higher molecular weight form of the LPSs. All the PS1 fractions contain methylated sugars, 2-amino-2,6-dideoxyhexose, heptose, glucuronic acid, and 2-keto-3-deoxyoctonic acid (KDO). All the PS2 fractions contain galacturonic acid, mannose, galactose, and KDO. The PS2 fractions have a molecular weight of about 700. The KDO is present at the reducing end of both the PS1 and the PS2 fractions. The PS1 and PS2 fractions from the mutants contain more glucose than these fractions from the parent. The LPS from a deletion mutant contains less acyl groups than the other LPSs. Immunoblots of the LPSs show that the parent and nod A mutant LPSs contain an additional antigenic band which is not observed in the other LPSs.

Journal Article↗
PubMed2002

Reduced gravitropism in inflorescence stems and hypocotyls, but not roots, of Arabidopsis mutants with large plastids.

The sites of gravity perception are columella cells in roots and endodermal cells in hypocotyls and inflorescence stems. Since plastids are likely to play a role in graviperception, we investigated gravitropism in plastid mutants of Arabidopsis. Previous studies have shown that the arc6 and arc12 (accumulation and replication of chloroplasts) mutants have an average of two large plastids per leaf mesophyll cell. In this study, we found that these arc mutants have altered plastid morphology throughout the entire plant body, including the cells involved in gravity perception. There were no major differences in total starch content per cell in endodermal and columella cells of the wild-type (WT) compared to arc6 and arc12 as assayed by iodine staining. Thus, the total mass of plastids per cell in arc6 and arc12 is similar to their respective WT strains. Results from time course of curvature studies demonstrated that the plastid mutation affected gravitropism only of inflorescence stems and hypocotyls, but not roots. Thus, roots appear to have different mechanisms of gravitropism compared to stems and hypocotyls. Time course of curvature studies with light-grown seedlings were performed in the presence of latrunculin B (Lat-B), an actin-depolymerizing drug. Lat-B promoted gravitropic curvature in hypocotyls of both the WT and arc6 but had little or no effect on gravitropism in roots of both strains. These results suggest that F-actin is not required for hypocotyl gravitropism.

Journal Article↗