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At least 505 records · Page 28Linked to original sources
PubMed1997

Epidermal cell differentiation in Arabidopsis determined by a Myb homolog, CPC.

The roots of plants normally carry small hairs arranged in a regular pattern. Transfer DNA-tagged lines of Arabidopsis thaliana included a mutant with few, randomly distributed root hairs. The mutated gene CAPRICE (CPC) encoded a protein with a Myb-like DNA binding domain typical of transcription factors involved in animal and plant development. Analysis in combination with other root hair mutations showed that CPC may work together with the TTG gene and upstream of the GL2 gene. Transgenic plants overexpressing CPC had more root hairs and fewer trichomes than normal. Thus, the CPC gene determines the fate of epidermal cell differentiation in Arabidopsis.

Amino Acid Sequence↗
PubMed2005

Functional genomic analysis of the AUXIN RESPONSE FACTOR gene family members in Arabidopsis thaliana: unique and overlapping functions of ARF7 and ARF19.

The AUXIN RESPONSE FACTOR (ARF) gene family products, together with the AUXIN/INDOLE-3-ACETIC ACID proteins, regulate auxin-mediated transcriptional activation/repression. The biological function(s) of most ARFs is poorly understood. Here, we report the identification and characterization of T-DNA insertion lines for 18 of the 23 ARF gene family members in Arabidopsis thaliana. Most of the lines fail to show an obvious growth phenotype except of the previously identified arf2/hss, arf3/ett, arf5/mp, and arf7/nph4 mutants, suggesting that there are functional redundancies among the ARF proteins. Subsequently, we generated double mutants. arf7 arf19 has a strong auxin-related phenotype not observed in the arf7 and arf19 single mutants, including severely impaired lateral root formation and abnormal gravitropism in both hypocotyl and root. Global gene expression analysis revealed that auxin-induced gene expression is severely impaired in the arf7 single and arf7 arf19 double mutants. For example, the expression of several genes, such as those encoding members of LATERAL ORGAN BOUNDARIES domain proteins and AUXIN-REGULATED GENE INVOLVED IN ORGAN SIZE, are disrupted in the double mutant. The data suggest that the ARF7 and ARF19 proteins play essential roles in auxin-mediated plant development by regulating both unique and partially overlapping sets of target genes. These observations provide molecular insight into the unique and overlapping functions of ARF gene family members in Arabidopsis.

Arabidopsis↗
PubMed1992

Molecular genetic approaches to plant development.

Higher plant morphogenesis has received renewed interest over the past few years. The improvement of molecular genetic approaches to generate tagged developmental mutants, for instance by T-DNA insertion, facilitated the isolation and characterization of the altered genes. Here we present recent progress on flower and root morphogenesis in the small crucifer Arabidopsis thaliana. The current model of Arabidopsis flower development is presented. We report on FLOWER1 (Fl1), which is a T-DNA-tagged ap2 allele. Our observations indicate that this Fl1 mutant has, besides the homeotic Ap2 phenotype, an aberrant seed coat, suggesting that this gene has also a function late in flower development. Furthermore, we present a brief summary about root development and focus on the super root (Sur) mutant, which is an ethyl methanesulfonate-induced mutant that produces excess lateral roots. Root explants of the Sur mutant, that do not develop further than the 4-leaf stage, can be induced to produce normal-looking shoots and flowers by addition of only cytokinin to the medium. The phenotype of Sur and its relation to the action of phytohormones is discussed.

Morphogenesis↗
PubMed2002

An Arabidopsis mutant defective in jasmonate response is allelic to the auxin-signaling mutant axr1.

A screen for Arabidopsis mutants that were insensitive to methyl jasmonate (MeJA) in an assay for seedling root growth yielded only alleles of previously isolated mutants jar1 and coi1, with one exception. Mapping of the locus and morphological characterization of the new mutant suggested it might be allelic to axr1, which had not previously been reported to show resistance to MeJA. The F(1) from a cross of the new mutant with axr1-3 did not show complementation, confirming that these are the same genes. The new allele is called axr1-24. In addition to MeJA and indole-3-acetic acid (IAA), axr1-24 had decreased sensitivity to 1-aminocyclopropane-1-carboxylic acid, 6-benzylamino-purine, epi-brassinolide, and abscisic acid. Both axr1-24 and the previously characterized axr1-3 allele were shown to be susceptible to the opportunistic pathogen Pythium irregulare, a trait found in other jasmonate response mutants, including jar1-1. The double mutant jar1-1/axr1-3 was more resistant to inhibition of root growth by MeJA and was more susceptible to P. irregulare infection than either single mutant, suggesting these genes might act in independent response pathways. In contrast, resistance to IAA in the double mutant was not different from axr1-3. Northern-blot analysis showed that IAA induced the jasmonate-responsive lipoxygenase 2, AOS, and AtVSP gene transcripts and induction was strongly impaired in axr1-3. However, transcript induction by MeJA was only minimally affected in axr1-3. This study demonstrates that in addition to auxin signaling, the AXR1 locus is involved in MeJA response, providing a mechanistic link between jasmonate and auxin-signaling pathways.

Abscisic Acid↗
PubMed1989

Selection and initial characterization of partially nitrate tolerant nodulation mutants of soybean.

Since NO(3) (-) availability in the rooting medium seriously limits symbiotic N(2) fixation by soybean (Glycine max [L.] Merr.), studies were initiated to select nodulation mutants which were more tolerant to NO(3) (-) and were adapted to the Midwest area of the United States. Three independent mutants were selected in the M(2) generation from ethyl methanesulfonate or N-nitroso-N-methylurea mutagenized Williams seed. All three mutants (designated NOD1-3, NOD2-4, and NOD3-7) were more extensively nodulated (427 to 770 nodules plant(-1)) than the Williams parent (187 nodules plant(-1)) under zero-N growth conditions. This provided evidence that the mutational event(s) affected autoregulatory control of nodulation. Moreover, all three mutants were partially tolerant to NO(3) (-); each retained greater acetylene reduction activity when grown hydroponically with 15 millimolar NO(3) (-) than did Williams at 1.5 millimolar NO(3) (-). The NO(3) (-) tolerance did not appear to be related to an altered ability to take up or metabolize NO(3) (-), based on solution NO(3) (-) depletion and on in vivo nitrate reductase assays. Enhanced nodulation appeared to be controlled by the host plant, being consistent across four Bradyrhizobium japonicum strains tested. In general, the mutant lines produced less dry weight than the control, with root dry weights being more affected than shoot dry weights. The nodulation trait has been stable through the M(5) generation in all three mutants.

Journal Article↗
PubMed1980

The development of sensory ganglion cells in normal and Sprawling mutant mice.

The foetal and early post-natal development of dorsal root ganglion cells in normal and Sprawling (Swl) mutant mice was studied by light and electron microscopy. As early as the 11th foetal day the nucleus of some neurons showed an indentation of its membrane and by the 13th day this abnormality was marked and present in many ganglion cells of foetuses which were, therefore, identified as presumptive Swl'. A peripherally situated nucleus and the aggregation of filaments and organelles in the central perikaryon were also early abnormalities, similar to those of the sensory neurons of the adult Swl mouse. In the normal ganglion cells, nuclei were rounded and central by the 16th foetal day and nuclear indentations were never seen, thus making a clear distinction possible between normal and Swl foetuses.

Animals↗
PubMed1990

Expression of glutamine synthetase genes in roots and nodules of Phaseolus vulgaris following changes in the ammonium supply and infection with various Rhizobium mutants.

In this paper we have examined whether the four glutamine synthetase (gln) genes, expressed in roots and nodules of Phaseolus vulgaris are substrate-inducible by ammonium. Manipulation of the ammonium pool in roots, through addition and removal of exogenous ammonium, did not elicit any changes in the abundances of the four mRNAs thus suggesting that the gln genes in roots of this legume are neither substrate-inducible by ammonium nor derepressed during nitrogen starvation. In nodules the effect of the ammonium supply on expression of the gln genes has been examined by growing nodules under argon/oxygen atmospheres, or with a number of Fix- Rhizobium mutants, and following addition of exogenous ammonium. The results of these experiments suggest that the expression of the gln-gamma gene, which is strongly induced during nodule development, is primarily under a developmental control. However nitrogen fixation appears to have a quantitative effect on expression of gln-gamma as the abundance of this mRNA is about 2 to 4-fold higher under nitrogen-fixing conditions. This effect could not be mimicked by addition of exogenous ammonium and moreover is not specific to the gln-gamma gene as mRNA from a leghaemoglobin gene was similarly affected. Taken together these results have failed to find an effect of ammonium on specifically inducing the expression of glutamine synthetase genes in roots and nodules of P. vulgaris.

Ammonia↗
PubMed2002

The Arabidopsis SKU5 gene encodes an extracellular glycosyl phosphatidylinositol-anchored glycoprotein involved in directional root growth.

To investigate how roots respond to directional cues, we characterized a T-DNA-tagged Arabidopsis mutant named sku5 in which the roots skewed and looped away from the normal downward direction of growth on inclined agar surfaces. sku5 roots and etiolated hypocotyls were slightly shorter than normal and exhibited a counterclockwise (left-handed) axial rotation bias. The surface-dependent skewing phenotype disappeared when the roots penetrated the agar surface, but the axial rotation defect persisted, revealing that these two directional growth processes are separable. The SKU5 gene belongs to a 19-member gene family designated SKS (SKU5 Similar) that is related structurally to the multiple-copper oxidases ascorbate oxidase and laccase. However, the SKS proteins lack several of the conserved copper binding motifs characteristic of copper oxidases, and no enzymatic function could be assigned to the SKU5 protein. Analysis of plants expressing SKU5 reporter constructs and protein gel blot analysis showed that SKU5 was expressed most strongly in expanding tissues. SKU5 was glycosylated and modified by glycosyl phosphatidylinositol and localized to both the plasma membrane and the cell wall. Our observations suggest that SKU5 affects two directional growth processes, possibly by participating in cell wall expansion.

Arabidopsis↗
PubMed2005

PGP4, an ATP binding cassette P-glycoprotein, catalyzes auxin transport in Arabidopsis thaliana roots.

Members of the ABC (for ATP binding cassette) superfamily of integral membrane transporters function in cellular detoxification, cell-to-cell signaling, and channel regulation. More recently, members of the multidrug resistance P-glycoprotein (MDR/PGP) subfamily of ABC transporters have been shown to function in the transport of the phytohormone auxin in both monocots and dicots. Here, we report that the Arabidopsis thaliana MDR/PGP PGP4 functions in the basipetal redirection of auxin from the root tip. Reporter gene studies showed that PGP4 was strongly expressed in root cap and epidermal cells. PGP4 exhibits apolar plasma membrane localization in the root cap and polar localization in tissues above. Root gravitropic bending and elongation as well as lateral root formation were reduced in pgp4 mutants compared with the wild type. pgp4 exhibited reduced basipetal auxin transport in roots and a small decrease in shoot-to-root transport consistent with a partial loss of the redirective auxin sink in the root. Seedlings overexpressing PGP4 exhibited increased shoot-to-root auxin transport. Heterologous expression of PGP4 in mammalian cells resulted in 1-N-naphthylthalamic acid-reversible net uptake of [3H]indole-3-acetic acid. These results indicate that PGP4 functions primarily in the uptake of redirected or newly synthesized auxin in epidermal root cells.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed1996

SOS1, a Genetic Locus Essential for Salt Tolerance and Potassium Acquisition.

To begin to determine which genes are essential for salt tolerance in higher plants, we identified four salt-hypersensitive mutants of Arabidopsis by using a root-bending assay on NaCl-containing agar plates. These mutants (sos1-1, sos1-2, sos1-3, and sos1-4) are allelic to each other and were caused by single recessive nuclear mutations. The SOS1 gene was mapped to chromosome 2 at 29.5 [plusmn] 6.1 centimorgans. The mutants showed no phenotypic changes except that their growth was >20 times more sensitive to inhibition by NaCl. Salt hypersensitivity is a basic cellular trait exhibited by the mutants at all developmental stages. The sos1 mutants are specifically hypersensitive to Na+ and Li+. The mutants were unable to grow on media containing low levels (below ~1 mM) of potassium. Uptake experiments using 86Rb showed that sos1 mutants are defective in high-affinity potassium uptake. sos1 plants became deficient in potassium when treated with NaCl. The results demonstrate that potassium acquisition is a critical process for salt tolerance in glycophytic plants.

Journal Article↗
PubMed1997

Characterization of a salicylic acid-insensitive mutant (sai1) of Arabidopsis thaliana, identified in a selective screen utilizing the SA-inducible expression of the tms2 gene.

Salicylic acid (SA) plays an important signaling role in the resistance of many plants to pathogen invasion. Increases in endogenous SA levels have been associated with the hypersensitive response as well as systemic acquired resistance (SAR). SA also induces the expression of a subset of the pathogenesis-related (PR) genes. However, relatively little is known about the events occurring subsequent to SA accumulation during a resistance response. In order to identify mutations in components of the SA signal transduction pathway, we have developed a genetic screen in Arabidopsis thaliana that utilizes the Agrobacterium tumefaciens tms2 gene as a counter-selectable marker. SA-inducible expression of the tms2 gene from the tobacco PR-1a promoter confers sensitivity to alpha-naphthalene acetamide (alpha-NAM), resulting in inhibition of root growth in germinating transgenic Arabidopsis seedlings. Mutants in which root growth is insensitive to alpha-NAM have been selected from this PR-1a:tms2 transgenic line with the expectation that a subset will lack a regulatory component downstream of SA. The sail mutant so identified expressed neither the PR-1a:tms2 transgene nor the endogenous Arabidopsis PR-1, PR-2, and PR-5 genes in response to SA. These genes also were not induced in sai1 by 2,6-dichloroisonicotinic acid (INA) or benzothiadiazole (BTH), two chemical inducers of SAR. As expected of a mutation acting downstream of SA, sai1 plants accumulate SA and its glucoside in response to infection with an avirulent pathogen and are more susceptible to this avirulent pathogen than the wild-type parent. sai1 is allelic to npr1, a previously identified SA-noninducible mutation. The recessive nature of the noninducible sai1 mutation suggests that the wild-type SAI1 gene acts as a positive regulator in the SA signal transduction pathway.

Amidohydrolases↗
PubMed1991

Efficiency of nodule initiation and autoregulatory responses in a supernodulating soybean mutant.

We compared the formation of nodules on the primary roots of a soybean cultivar (Glycine max (L.) Merr. cv. Bragg) and a supernodulating mutant derivative, nts382. Inoculation with Bradyrhizobium japonicum USDA 110 at different times after seed imbibition showed that the roots acquired full susceptibility to infection only between 3 and 4 days postgermination. When the plants were inoculated with serial dilutions of a bacterial suspension, the number of nodules formed in the initially susceptible region of the roots was linearly dependent on the logarithm of the inoculum dose until an optimum dose was reached. At least 10-fold-lower doses were required to induce half-maximal nodulation responses on nts382 than on the wild type. However, at optimal doses, about six times as many nodules formed in the initially susceptible region of the roots in nts382. Since there was no appreciable difference in the apparent rates of nodule emergence, the increased efficiency of nodule initiation in the supernodulating mutant could have resulted from a lower threshold of response to bacterial symbiotic signals. Two inoculations (24 h apart) of G. max cv. Bragg revealed that there was a host-mediated regulatory response that suppressed nodulation in younger portions of the primary roots, as reported previously for other soybean cultivar-Bradyrhizobium combinations. Similar experiments with nts382 revealed a comparable suppressive response, but this response was not as pronounced as it was in the wild type. This and other results suggest that there are additional control mechanisms for nodulation that are different from the systemic autoregulatory control of nodulation altered in supernodulating mutants.

Journal Article↗
PubMed2005

Isolation and characterization of a Ds-tagged rice (Oryza sativa L.) GA-responsive dwarf mutant defective in an early step of the gibberellin biosynthesis pathway.

We have isolated a severe dwarf transposon (Ds) insertion mutant in rice (Oryza sativa L.), which could be differentiated early in the seedling stage by reduced shoot growth and dark green leaves, and later by severe dwarfism and failure to initiate flowering. These mutants, however, showed normal seed germination and root growth. One of the sequences flanking Ds, rescued from the mutant, was of a chromosome 4-located putative ent-kaurene synthase (KS) gene, encoding the enzyme catalyzing the second step of the gibberellin (GA) biosynthesis pathway. Dwarf mutants were always homozygous for this Ds insertion and no normal plants homozygous for this mutation were recovered in the segregating progeny, indicating that the Ds insertion mutation is recessive. As mutations in three recently reported rice GA-responsive dwarf mutant alleles and the dwarf mutation identified in this study mapped to the same locus, we designate the corresponding gene OsKS1. The osks1 mutant seedlings were responsive to exogenous gibberellin (GA3). OsKS1 transcripts of about 2.3 kb were detected in leaves and stem of wild-type plants, but not in germinating seeds or roots, suggesting that OsKS1 is not involved in germination or root growth. There are at least five OsKS1-like genes in the rice genome, four of which are also represented in rice expressed sequence tag (EST) databases. All OsKS1-like genes are transcribed with different expression patterns. ESTs corresponding to all six OsKS genes are represented in other cereal databases including barley, wheat and maize, suggesting that they are biologically active.

Alkyl and Aryl Transferases↗
PubMed2004

ENHANCER of TRY and CPC 2 (ETC2) reveals redundancy in the region-specific control of trichome development of Arabidopsis.

An evolutionarily conserved set of proteins consisting of MYB and bHLH transcription factors and a WD40 domain protein is known to act in concert to control various developmental processes including trichome and root hair development. Their function is difficult to assess because most of them belong to multigene families and appear to act in a redundant fashion. In this study we identified an enhancer of the two root hair and trichome patterning mutants triptychon (try) and caprice (cpc), enhancer of try and cpc2 (etc2). The ETC2 gene shows high sequence similarity to the single-repeat MYB genes CPC and TRY. Overexpression results in the suppression of trichomes and overproduction of root hairs similarly as observed for TRY and CPC suggesting that ETC2 has similar biochemical properties. The etc2 single mutant shows an increase in trichome number on leaves and petioles. Double and triple mutant analysis indicates that the ETC2 gene acts redundant with TRY and CPC in trichome patterning.

Amino Acid Sequence↗
PubMed2003

Genetic analysis of the gravitropic set-point angle in lateral roots of Arabidopsis.

Research on gravity responses in plants has mostly focused on primary roots and shoots, which typically orient to a vertical orientation. However, the distribution of lateral organs and their characteristically non-vertical growth orientation are critical for the determination of plant form. For example, in Arabidopsis, when lateral roots emerge from the primary root, they grow at a nearly horizontal orientation. As they elongate, the roots slowly curve until they eventually reach a vertical orientation. The regulation of this lateral root orientation is an important component affecting overall root system architecture. We found that this change in orientation is not simply due to the onset of gravitropic competence, as non-vertical lateral roots are capable of both positive and negative gravitropism. Thus, the horizontal growth of new lateral roots appears to be determined by what is called the gravitropic set-point angle (GSA). This developmental control of the GSA of lateral roots in Arabidopsis provides a useful system for investigating the components involved in regulating gravitropic responses. Using this system, we have identified several Arabidopsis mutants that have altered lateral root orientations but maintain normal primary root orientation.

Arabidopsis↗
PubMed2002

Characterization of LPS mutants of peanut specific Bradyrhizobium (GN17).

Two mutants of Bradyrhizobium sp. (Arachis) strain GN17 having altered lipopolysaccharide (LPS) composition were isolated upon random Tn5 mutagenesis to study their binding with peanut root lectin (PRA II). These mutant strains designated as GN17M1 and GN17M2 produced rough colonies and showed autoagglutination. Flow cytometric analyses indicated that strain GN17M1 bind to PRA II with highest efficiency. Both the mutants synthesized only high molecular weight lipopolysaccharides as observed by silver staining of polyacrylamide gel. The LPSs from both the mutants cross-reacted with anti-GN17 LPS, however, GN17M1 LPS showed 3 times higher cross-reactivity as detected by ELISA. Carbohydrate analysis by high performance anion exchange chromatography (HPAEC) showed that glucose was the major constituent of the purified LPS from the parent strain whereas mannose appeared as major component in the GN17M2 LPS. Equivalent amount of glucose and galactosamine with significant amount of mannose and galactose was the characteristics of the GN17M1 LPS. Purified LPS from GN17M1 and GN17M2 were respectively 17 and 10 times more potent inhibitors of PRA II activity than that of parent strain GN17. Similar binding efficiencies of the mutant LPS towards PRA II was also observed by ELISA. The results of this study indicate that the composition and the arrangement of the LPS are crucial for lectin binding.

Arachis↗
PubMed1974

Physiology of the Yellow-Green 6 Gene in Tomato: A Possible Interrelationship between the Phenotypic Expressions of the Yellow-Green 6 Gene Mutation and the Gibberellins.

The yellow-green 6 (yg(6)) mutation in tomato (Lycopersicon esculentum Mill.) is controlled by a single recessive gene with pleiotropic effects. The syndrome of characters associated with the mutation are enhanced stem elongation, reduced chlorophyll content and absence of detectable anthocyanins. We now have shown that the mutant also has fewer lateral roots than the wild type and higher l-phenylalanine ammonia-lyase (E.C. 4.3.1.5) activity than the normal tomato. These traits of the mutant closely resemble those induced in many plants by the application of gibberellic acid which suggests that the phenotypic expressions of the mutation might in some manner be related to the endogenous level or activity of the gibberellins. In support of this premise, data are presented which show that the characters of the mutant can be induced in the wild type tomato by application of gibberellic acid. Conversely, several traits of the wild type can be induced in the mutant by an inhibitor of gibberellin hiosynthesis, Phosfon. In addition, an embryoless barley half-seed bioassay for the gibberellins and gas-liquid chromatography indicated that the mutant contained at least three times as much total gibberellin as the wild type plant.

Journal Article↗
PubMed2005

A turanose-insensitive mutant suggests a role for WOX5 in auxin homeostasis in Arabidopsis thaliana.

Sugars acting as signalling molecules regulate many developmental processes in plants, including lateral and adventitious root production. Turanose, a non-metabolizable sucrose analogue, profoundly affects the growth pattern of Arabidopsis seedlings. Turanose-treated seedlings are characterized by a very short primary root and a short hypocotyl showing the production of adventitious roots. A turanose-insensitive (tin) mutant was identified and characterized. Because of a T-DNA insertion and a chromosomal translocation, tin expresses a chimeric form of WOX5, a gene known to be expressed in the root quiescent centre. The tin mutation can be complemented by overexpression of WOX5, suggesting it is a loss-of-function mutant. We found that WOX5 is both turanose- and auxin-inducible. Moreover, turanose insensitivity is associated with altered auxin homeostasis, as demonstrated by the constitutive activation of indole acetic acid (IAA) conjugation and SUPERROOT2 expression in tin. On the basis of turanose effects on wild-type seedlings and the tin molecular and hormonal phenotype, we propose a role for WOX5 in the root apical meristem as a negative trigger of IAA homeostatic mechanisms allowing the maintenance of a restricted area of auxin maximum, which is required for a correct root-formation pattern.

Arabidopsis↗