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At least 397 records · Page 22Linked to original sources
PubMed1998

Regulation of nitrate reductase transcript levels by glutamine accumulating in the leaves of a ferredoxin-dependent glutamate synthase-deficient gluS mutant of Arabidopsis thaliana, and by glutamine provided via the roots.

The regulation by glutamine of the leaf transcript level corresponding to the Arabidopsis thaliana (L.) Heynh. nitrate reductase gene nia2 was examined using a novel approach: we took advantage of the ability of a ferredoxin-dependent glutamate synthase-deficient gluS mutant of A. thaliana to accumulate glutamine in the leaves when illuminated under conditions that favour photorespiration. The accumulation of glutamine in gluS mutant leaves and the concomitant decline in the leaf glutamate pool were not correlated with a reduction in the foliar nia2 transcript level. This result indicates that glutamine may not exert a negative control of the leaf nia2 transcript pool. The pattern of diurnal nia2 mRNA oscillation did not change upon illumination of the gluS mutant in air, although the leaf glutamine level remained high during the diurnal cycle. The amplitude of the diurnal fluctuation in nia2 transcript abundance, therefore, does not seem to depend on the size of the leaf glutamine pool (which normally fluctuates in opposite phase). This result also appears to argue against a role of glutamine as an effective repressor of nia2 transcript accumulation. The application of a solution containing 100 mM glutamine to the roots of A. thaliana resulted in an increase in the leaf glutamine level and in a decrease in the leaf nia2 transcript level. Net CO2 uptake and chlorophyll fluorescence quenching by attached leaves of A. thaliana were determined as a control of the physiological status of the plants and remained unaffected by the glutamine treatment. However, there was a decrease in the foliar nitrate level. The negative effect on the nia2 transcript pool exerted by exogeneous glutamine may, therefore, be explained as a result of the down-regulation of nitrate-uptake permeases in the roots by glutamine.

Amino Acid Oxidoreductases↗
PubMed2002

Water uptake and hydraulic properties of elongating cells in hydrotropically bending roots of Pisum sativum L.

The water potential and hydraulic conductivity (Lp) of elongating cells in hydrotropically bending roots of the ageotropic mutant ageotropum of pea (Pisum sativum L.) were measured in situ. When agar blocks with water potentials of -0.03 and -0.8 MPa were unilaterally applied directly to a root tip, cells in the most rapidly elongating zone, 3-4 mm from the tip, showed marked differential growth. The rate of water uptake by a cell on the side treated with an agar block with a lower water potential was significantly larger in the outer first and second layers of cortex than on the other side. There were no differences in the values of turgor pressure, osmotic potential and calculated water potential between the two sides either in elongating or in mature cells, indicating the absence of any difference in the growth-induced water potential on the two sides of the root. Lp was significantly larger on the side with the agar block with lower water potential. The results suggest that the difference in the rate of water uptake during the differential cell growth that occurs during root hydrotropism might be induced mainly by a change in Lp.

Cell Differentiation↗
PubMed2005

The potassium transporter AtHAK5 functions in K(+) deprivation-induced high-affinity K(+) uptake and AKT1 K(+) channel contribution to K(+) uptake kinetics in Arabidopsis roots.

Potassium is an important macronutrient and the most abundant cation in plants. Because soil mineral conditions can vary, plants must be able to adjust to different nutrient availabilities. Here, we used Affymetrix Genechip microarrays to identify genes responsive to potassium (K(+)) deprivation in roots of mature Arabidopsis (Arabidopsis thaliana) plants. Unexpectedly, only a few genes were changed in their expression level after 6, 48, and 96 h of K(+) starvation even though root K(+) content was reduced by approximately 60%. AtHAK5, a potassium transporter gene from the KUP/HAK/KT family, was most consistently and strongly up-regulated in its expression level across 48-h, 96-h, and 7-d K(+) deprivation experiments. AtHAK5 promoter-beta-glucuronidase and -green fluorescent protein fusions showed AtHAK5 promoter activity in the epidermis and vasculature of K(+) deprived roots. Rb(+) uptake kinetics in roots of athak5 T-DNA insertion mutants and wild-type plants demonstrated the absence of a major part of an inducible high-affinity Rb(+)/K(+) (K(m) approximately 15-24 microm) transport system in athak5 plants. In comparative analyses, uptake kinetics of the K(+) channel mutant akt1-1 showed that akt1-1 roots are mainly impaired in a major transport mechanism, with an apparent affinity of approximately 0.9 mm K(+)(Rb(+)). Data show adaptation of apparent K(+) affinities of Arabidopsis roots when individual K(+) transporter genes are disrupted. In addition, the limited transcriptome-wide response to K(+) starvation indicates that posttranscriptional mechanisms may play important roles in root adaptation to K(+) availability in Arabidopsis. The results demonstrate an in vivo function for AtHAK5 in the inducible high-affinity K(+) uptake system in Arabidopsis roots.

Arabidopsis↗
PubMed2000

Genetic interactions during root hair morphogenesis in Arabidopsis.

Root hairs are a major site for the uptake of water and nutrients into plants and form an increasingly important model system for studies of development of higher plants and cell biology. We have identified loss-of-function mutations in eight new genes required for hair growth in Arabidopsis: SHAVEN1 (SHV1), SHV2, and SHV3; CENTIPEDE1 (CEN1), CEN2, and CEN3; BRISTLED1 (BST1); and SUPERCENTIPEDE1 (SCN1). We combined mutations in 79 pairs of genes to determine the stages at which these and six previously known genes contribute to root hair formation. Double mutant phenotypes revealed roles for several genes that could not have been predicted from the single mutant phenotypes. For example, we show that TIP1 and RHD3 are required much earlier in hair formation than previous studies have suggested. We present a genetic model for root hair morphogenesis that defines the roles of each gene, and we suggest hypotheses about functional relationships between genes.

Arabidopsis↗
PubMed2003

AtAGP30, an arabinogalactan-protein in the cell walls of the primary root, plays a role in root regeneration and seed germination.

Arabinogalactan-proteins (AGPs) are extracellular proteoglycans that are implicated in many plant growth and developmental processes, but in no case has a biological function been assigned to a particular AGP. AtAGP30 is a non-classical AGP core protein from Arabidopsis that is expressed only in roots. Analysis of the corresponding mutant, agp30, has revealed that the wild-type gene product is required in vitro for root regeneration and in planta for the timing of seed germination. The mutant shows a suppression of the abscisic acid (ABA)-induced delay in germination and altered expression of some ABA-regulated genes. This suggests that AtAGP30 functions in the ABA response. By analogy to proteoglycan-mediated regulation of growth-factor-signalling pathways in animals, our data indicate that phytohormone activity in plants can be modulated by AGPs.

Amino Acid Sequence↗
PubMed2005

Pseudomonas fluorescens and Glomus mosseae trigger DMI3-dependent activation of genes related to a signal transduction pathway in roots of Medicago truncatula.

Plant genes induced during early root colonization of Medicago truncatula Gaertn. J5 by a growth-promoting strain of Pseudomonas fluorescens (C7R12) have been identified by suppressive subtractive hybridization. Ten M. truncatula genes, coding proteins associated with a putative signal transduction pathway, showed an early and transient activation during initial interactions between M. truncatula and P. fluorescens, up to 8 d after root inoculation. Gene expression was not significantly enhanced, except for one gene, in P. fluorescens-inoculated roots of a Myc(-)Nod(-) genotype (TRV25) of M. truncatula mutated for the DMI3 (syn. MtSYM13) gene. This gene codes a Ca(2+) and calmodulin-dependent protein kinase, indicating a possible role of calcium in the cellular interactions between M. truncatula and P. fluorescens. When expression of the 10 plant genes was compared in early stages of root colonization by mycorrhizal and rhizobial microsymbionts, Glomus mosseae activated all 10 genes, whereas Sinorhizobium meliloti only activated one and inhibited four others. None of the genes responded to inoculation by either microsymbiont in roots of the TRV25 mutant. The similar response of the M. truncatula genes to P. fluorescens and G. mosseae points to common molecular pathways in the perception of the microbial signals by plant roots.

Base Sequence↗
PubMed2002

Cell specification in the Arabidopsis root epidermis requires the activity of ECTOPIC ROOT HAIR 3--a katanin-p60 protein.

The Arabidopsis root is composed of radial cell layers, each with distinct identities. The epidermal layer is composed of rows of hair cells flanked on either side by rows of non-hair epidermal cells. The development of hair and non-hair cells is dependent on domains of positional information with strict boundaries. The pattern of cell differentiation and the expression of molecular markers of cell fate is altered in the ectopic root hair 3 (erh3) mutant epidermis indicating that ERH3 is required for the specification of cell fates from early in development (in the meristem) through differentiation. Furthermore the expression of molecular markers indicates that the specification of cell identities is defective within other radial cell layers. ERH3 encodes a p60 katanin protein that is expressed throughout the plant. Katanin proteins are known to sever microtubules, and have a role in the organisation of the plant cell wall since mutants with decreased katanin activity have been shown to have defective walls. We suggest that microtubules are involved in the specification of cell identities in cells of the Arabidopsis root. Microtubules may be required for the localization of positional cues in the wall that have previously been shown to operate in the development of the root epidermis. Alternatively microtubules may be involved in another as yet undefined process required for the specification of cell identity in plants.

Adenosine Triphosphatases↗
PubMed2004

The ubiquitin ligase XBAT32 regulates lateral root development in Arabidopsis.

Ubiquitin-mediated protein modification plays a key role in many cellular signal transduction pathways. The Arabidopsis gene XBAT32 encodes a protein containing an ankyrin repeat domain at the N-terminal half and a RING finger motif. The XBAT32 protein is capable of ubiquitinating itself. Mutation in XBAT32 causes a number of phenotypes including severe defects in lateral root production and in the expression of the cell division marker CYCB1;1::GUS. The XBAT32 gene is expressed abundantly in the vascular system of the primary root, but not in newly formed lateral root primordia. Treatment with auxin increases the expression of XBAT32 in the primary root and partially rescues the lateral root defect in xbat32-1 mutant plants. Thus, XBAT32 is a novel ubiquitin ligase required for lateral root initiation.

Alleles↗
PubMed1992

Hydrotropism in pea roots in a porous-tube water delivery system.

Orientation of root growth on earth and under microgravity conditions can possibly be controlled by hydrotropism--growth toward a moisture source in the absence of or reduced gravitropism. A porous-tube water delivery system being used for plant growth studies is appropriate for testing this hypothesis since roots can be grown aeroponically in this system. When the roots of the agravitropic mutant pea ageotropum (Pisum sativum L.) were placed vertically in air of 91% relative humidity and 2 to 3 mm from the water-saturated porous tube placed horizontally, the roots responded hydrotropically and grew in a continuous arch along the circular surface of the tube. By contrast, normal gravitropic roots of Alaska' pea initially showed a slight transient curvature toward the tube and then resumed vertical downward growth due to gravitropism. Thus, in microgravity, normal gravitropic roots could respond to a moisture gradient as strongly as the agravitropic roots used in this study. Hydrotropism should be considered a significant factor responsible for orientation of root growth in microgravity.

Equipment Design↗
PubMed1992

Methyl jasmonate inhibition of root growth and induction of a leaf protein are decreased in an Arabidopsis thaliana mutant.

Jasmonic acid and its methyl ester, methyl jasmonate (MeJA), are plant signaling molecules that affect plant growth and gene expression. Primary root growth of wild-type Arabidopsis thaliana seedlings was inhibited 50% when seedlings were grown on agar medium containing 0.1 M MeJA. An ethyl methanesulfonate mutant (jar1) with decreased sensitivity to MeJA inhibition of root elongation was isolated and characterized. Genetic data indicated the trait was recessive and controlled by a single Mendelian factor. MeJA-induced polypeptides were detected in Arabidopsis leaves by antiserum to a MeJA-inducible vegetative storage protein from soybean. The induction of these proteins by MeJA in the mutant was at least 4-fold less in jar1 compared to wild type. In contrast, seeds of jar1 plants were more sensitive than wild type to inhibition of germination by abscisic acid. These results suggest that the defect in jar1 affects a general jasmonate response pathway, which may regulate multiple genes in different plant organs.

Journal Article↗
PubMed2000

Root colonization by phenazine-1-carboxamide-producing bacterium Pseudomonas chlororaphis PCL1391 is essential for biocontrol of tomato foot and root rot.

The phenazine-1-carboxamide-producing bacterium Pseudomonas chlororaphis PCL1391 controls tomato foot and root rot caused by Fusarium oxysporum f. sp. radicislycopersici. To test whether root colonization is required for biocontrol, mutants impaired in the known colonization traits motility, prototrophy for amino acids, or production of the site-specific recombinase, Sss/XerC were tested for their root tip colonization and biocontrol abilities. Upon tomato seedling inoculation, colonization mutants of strain PCL1391 were impaired in root tip colonization in a gnotobiotic sand system and in potting soil. In addition, all mutants were impaired in their ability to control tomato foot and root rot, despite the fact that they produce wild-type levels of phenazine-1-carboxamide, the antifungal metabolite previously shown to be required for biocontrol. These results show, for what we believe to be the first time, that root colonization plays a crucial role in biocontrol, presumably by providing a delivery system for antifungal metabolites. The ability to colonize and produce phenazine-1-carboxamide is essential for control of F. oxysporum f. sp. radicis-lycopersici. Furthermore, there is a notable overlap of traits identified as being important for colonization of the rhizosphere and animal tissues.

Amino Acid Sequence↗
PubMed2003

Arabidopsis actin gene ACT7 plays an essential role in germination and root growth.

Arabidopsis contains eight actin genes. Of these ACT7 is the most strongly expressed in young plant tissues and shows the greatest response to physiological cues. Adult plants homozygous for the act7 mutant alleles show no obvious above-ground phenotypes, which suggests a high degree of functional redundancy among plant actins. However, act7-1 mutant plants are at a strong selective disadvantage when grown in competition with wild-type plants and therefore must have undetected physical defects. The act7-1 and act7-4 alleles contain T-DNA insertions just after the stop codon and within the first intron, respectively. Homozygous mutant seedlings of both alleles showed less than 7% of normal ACT7 protein levels. Mutants displayed delayed and less efficient germination, increased root twisting and waving, and retarded root growth. The act7-4 mutant showed the most dramatic reduction in root growth. The act7-4 root apical cells were not in straight files and contained oblique junctions between cells suggesting a possible role for ACT7 in determining cell polarity. Wild-type root growth was fully restored to the act7-1 mutant by the addition of an exogenous copy of the ACT7 gene. T-DNA insertions just downstream of the major polyadenylation sites (act7-2, act7-3) appeared fully wild type. The act7 mutant phenotypes demonstrate a significant requirement for functional ACT7 protein during root development and explain the strong negative selection component seen for the act7-1 mutant.

Actins↗
PubMed1991

Light Microscopy Study of Nodule Initiation in Pisum sativum L. cv Sparkle and in Its Low-Nodulating Mutant E2 (sym 5).

We compared nodule initiation in lateral roots of Pisum sativum (L.) cv Sparkle and in a low-nodulating mutant E2 (sym 5). In Sparkle, about 25% of the infections terminated in the epidermis, a similar number stopped in the cortex, and 50% resulted in the formation of a nodule meristem or an emerged nodule. The mutant E2 (sym 5) was infected as often as was the parent, and it formed a normal infection thread. In the mutant, cell divisions rarely occurred in advance of the infection thread, and few nodule primordia were produced. Growing the mutant at a low root temperature or adding Ag(+) to the substrate increased the number of cell divisions and nodule primordia. We conclude that, in the E2 line, the infection process is arrested in the cortex, at the stage of initial cell divisions before the establishment of a nodule primordium.

Journal Article↗
PubMed1998

An isoflavonoid-inducible efflux pump in Agrobacterium tumefaciens is involved in competitive colonization of roots.

Agrobacterium tumefaciens 1D1609, which was originally isolated from alfalfa (Medicago sativa L.), contains genes that increase competitive root colonization on that plant by reducing the accumulation of alfalfa isoflavonoids in the bacterial cells. Mutant strain I-1 was isolated by its isoflavonoid-inducible neomycin resistance following mutagenesis with the transposable promoter probe Tn5-B30. Nucleotide sequence analysis showed the transposon had inserted in the first open reading frame, ifeA, of a three-gene locus (ifeA, ifeB, and ifeR), which shows high homology to bacterial efflux pump operons. Assays on alfalfa showed that mutant strain I-1 colonized roots normally in single-strain tests but was impaired significantly (P < or = 0.01) in competition against wild-type strain 1D1609. Site-directed mutagenesis experiments, which produced strains I-4 (ifeA::gusA) and I-6 (ifeA::omega-Tc), confirmed the importance of ifeA for competitive root colonization. Exposure to the isoflavonoid coumestrol increased beta-glucuronidase activity in strain I-4 21-fold during the period when coumestrol accumulation in wild-type cells declined. In the same test, coumestrol accumulation in mutant strain I-6 did not decline. Expression of the ifeA-gusA reporter was also induced by the alfalfa root isoflavonoids formononetin and medicarpin but not by two triterpenoids present in alfalfa. These results show that an efflux pump can confer measurable ecological benefits on A. tumefaciens in an environment where the inducing molecules are known to be present.

Agrobacterium tumefaciens↗
PubMed2001

The effect of the Agrobacterium tumefaciens attR mutation on attachment and root colonization differs between legumes and other dicots.

Infections of wound sites on dicot plants by Agrobacterium tumefaciens result in the formation of crown gall tumors. An early step in tumor formation is bacterial attachment to the plant cells. AttR mutants failed to attach to wound sites of both legumes and nonlegumes and were avirulent on both groups of plants. AttR mutants also failed to attach to the root epidermis and root hairs of nonlegumes and had a markedly reduced ability to colonize the roots of these plants. However, AttR mutants were able to attach to the root epidermis and root hairs of alfalfa, garden bean, and pea. The mutant showed little reduction in its ability to colonize these roots. Thus, A. tumefaciens appears to possess two systems for binding to plant cells. One system is AttR dependent and is required for virulence on all of the plants tested and for colonization of the roots of all of the plants tested except legumes. Attachment to root hairs through this system can be blocked by the acetylated capsular polysaccharide. The second system is AttR independent, is not inhibited by the acetylated capsular polysaccharide, and allows the bacteria to bind to the roots of legumes.

Agrobacterium tumefaciens↗
PubMed2005

AtbHLH29 of Arabidopsis thaliana is a functional ortholog of tomato FER involved in controlling iron acquisition in strategy I plants.

AtbHLH29 of Arabidopsis, encoding a bHLH protein, reveals a high similarity to the tomato FER which is proposed as a transcriptional regulator involved in controlling the iron deficiency responses and the iron uptake in tomato. For identification of its biological functions, AtbHLH29 was introduced into the genome of the tomato FER mutant T3238fer mediated by Agrobacterium tumefaciencs. Transgenic plants were regenerated and the stable integration of AtbHLH29 into their genomes was confirmed by Southern hybridization. Molecular analysis demonstrated that expression of the exogenous AtbHLH29 of Arabidopsis in roots of the FER mutant T3238fer enabled to complement the defect functions of FER. The transgenic plants regained the ability to activate the whole iron deficiency responses and showed normal growth as the wild type under iron-limiting stress. Our transformation data demonstrate that AtbHLH29 is a functional ortholog of the tomato FER and can completely replace FER in controlling the effective iron acquisition in tomato. Except of iron, FER protein was directly or indirectly involved in manganese homeostasis due to that loss functions of FER in T3238fer resulted in strong reduction of Mn content in leaves and the defect function on Mn accumulation in leaves was complemented by expression of AtbHLH29 in the transgenic plants. Identification of the similar biological functions of FER and AtbHLH29, which isolated from two systematically wide-diverged "strategy I" plants, suggests that FER might be a universal gene presented in all strategy I plants in controlling effective iron acquisition system in roots.

Arabidopsis↗
PubMed2004

Lateral roots affect the proteome of the primary root of maize (Zea mays L.).

Lateral roots are initiated from the pericycle cells of other types of roots and remain in contact with these roots throughout their life span. Although this physical contact has the potential to permit the exchange of signals, little is known about the flow of information from the lateral roots to the primary root. To begin to study these interactions the proteome of the primary root system of the maize (Zea mays L.) lrt1 mutant, which does not initiate lateral roots, was compared with the corresponding proteome of wild-type seedlings 9 days after germination. Approximately 150 soluble root proteins were resolved by two-dimensional electrophoresis and analyzed by MALDI-ToF mass spectrometry and database searching. The 96 most abundant proteins from a pH 4-7 gradient were analyzed; 67 proteins representing 47 different Genbank accessions were identified. Interestingly, 10 (15/150) of the detected proteins were preferentially expressed in lrt1 roots that lack lateral roots. Eight of these lrt1-specific proteins were identified and four are involved in lignin metabolism. This study demonstrates for the first time the influence of lateral roots on the proteome of the primary root system. To our knowledge this is the first study to demonstrate an interaction between two plant organs (viz., lateral and primary roots) at the level of the proteome.

Electrophoresis, Gel, Two-Dimensional↗