PubMed Health⌕ Search

Biomedical subjects

Christian Luschnig

Publications and source records attributed to Christian Luschnig.

12 recordsLinked to original sources
PubMed2006

Canalization of auxin flow by Aux/IAA-ARF-dependent feedback regulation of PIN polarity.

Plant development is characterized by a profound ability to regenerate and form tissues with new axes of polarity. An unsolved question concerns how the position within a tissue and cues from neighboring cells are integrated to specify the polarity of individual cells. The canalization hypothesis proposes a feedback effect of the phytohormone auxin on the directionality of intercellular auxin flow as a means to polarize tissues. Here we identify a cellular and molecular mechanism for canalization. Local auxin application, wounding, or auxin accumulation during de novo organ formation lead to rearrangements in the subcellular polar localization of PIN auxin transport components. This auxin effect on PIN polarity is cell-specific, does not depend on PIN transcription, and involves the Aux/IAA-ARF (indole-3-acetic acid-auxin response factor) signaling pathway. Our data suggest that auxin acts as polarizing cue, which links individual cell polarity with tissue and organ polarity through control of PIN polar targeting. This feedback regulation provides a conceptual framework for polarization during multiple regenerative and patterning processes in plants.

Arabidopsis↗
PubMed2006

PIN proteins perform a rate-limiting function in cellular auxin efflux.

Intercellular flow of the phytohormone auxin underpins multiple developmental processes in plants. Plant-specific pin-formed (PIN) proteins and several phosphoglycoprotein (PGP) transporters are crucial factors in auxin transport-related development, yet the molecular function of PINs remains unknown. Here, we show that PINs mediate auxin efflux from mammalian and yeast cells without needing additional plant-specific factors. Conditional gain-of-function alleles and quantitative measurements of auxin accumulation in Arabidopsis and tobacco cultured cells revealed that the action of PINs in auxin efflux is distinct from PGP, rate-limiting, specific to auxins, and sensitive to auxin transport inhibitors. This suggests a direct involvement of PINs in catalyzing cellular auxin efflux.

ATP-Binding Cassette Transporters↗
PubMed2006

The Arabidopsis MAX pathway controls shoot branching by regulating auxin transport.

BACKGROUND: Plants achieve remarkable plasticity in shoot system architecture by regulating the activity of secondary shoot meristems, laid down in the axil of each leaf. Axillary meristem activity, and hence shoot branching, is regulated by a network of interacting hormonal signals that move through the plant. Among these, auxin, moving down the plant in the main stem, indirectly inhibits axillary bud outgrowth, and an as yet undefined hormone, the synthesis of which in Arabidopsis requires MAX1, MAX3, and MAX4, moves up the plant and also inhibits shoot branching. Since the axillary buds of max4 mutants are resistant to the inhibitory effects of apically supplied auxin, auxin and the MAX-dependent hormone must interact to inhibit branching. RESULTS: Here we show that the resistance of max mutant buds to apically supplied auxin is largely independent of the known, AXR1-mediated, auxin signal transduction pathway. Instead, it is caused by increased capacity for auxin transport in max primary stems, which show increased expression of PIN auxin efflux facilitators. The max phenotype is dependent on PIN1 activity, but it is independent of flavonoids, which are known regulators of PIN-dependent auxin transport. CONCLUSIONS: The MAX-dependent hormone is a novel regulator of auxin transport. Modulation of auxin transport in the stem is sufficient to regulate bud outgrowth, independent of AXR1-mediated auxin signaling. We therefore propose an additional mechanism for long-range signaling by auxin in which bud growth is regulated by competition between auxin sources for auxin transport capacity in the primary stem.

Arabidopsis↗
PubMed2006

The TORNADO1 and TORNADO2 genes function in several patterning processes during early leaf development in Arabidopsis thaliana.

In multicellular organisms, patterning is a process that generates axes in the primary body plan, creates domains upon organ formation, and finally leads to differentiation into tissues and cell types. We identified the Arabidopsis thaliana TORNADO1 (TRN1) and TRN2 genes and their role in leaf patterning processes such as lamina venation, symmetry, and lateral growth. In trn mutants, the leaf venation network had a severely reduced complexity: incomplete loops, no tertiary or quaternary veins, and vascular islands. The leaf laminas were asymmetric and narrow because of a severely reduced cell number. We postulate that the imbalance between cell proliferation and cell differentiation and the altered auxin distribution in both trn mutants cause asymmetric leaf growth and aberrant venation patterning. TRN1 and TRN2 were epistatic to ASYMMETRIC LEAVES1 with respect to leaf asymmetry, consistent with their expression in the shoot apical meristem and leaf primordia. TRN1 codes for a large plant-specific protein with conserved domains also found in a variety of signaling proteins, whereas TRN2 encodes a transmembrane protein of the tetraspanin family whose phylogenetic tree is presented. Double mutant analysis showed that TRN1 and TRN2 act in the same pathway.

Arabidopsis↗
PubMed2006

Intracellular trafficking and proteolysis of the Arabidopsis auxin-efflux facilitator PIN2 are involved in root gravitropism.

Root gravitropism describes the orientation of root growth along the gravity vector and is mediated by differential cell elongation in the root meristem. This response requires the coordinated, asymmetric distribution of the phytohormone auxin within the root meristem, and depends on the concerted activities of PIN proteins and AUX1 - members of the auxin transport pathway. Here, we show that intracellular trafficking and proteasome activity combine to control PIN2 degradation during root gravitropism. Following gravi-stimulation, proteasome-dependent variations in PIN2 localization and degradation at the upper and lower sides of the root result in asymmetric distribution of PIN2. Ubiquitination of PIN2 occurs in a proteasome-dependent manner, indicating that the proteasome is involved in the control of PIN2 turnover. Stabilization of PIN2 affects its abundance and distribution, and leads to defects in auxin distribution and gravitropic responses. We describe the effects of auxin on PIN2 localization and protein levels, indicating that redistribution of auxin during the gravitropic response may be involved in the regulation of PIN2 protein.

Arabidopsis↗
PubMed2006

Transcriptome analysis of bud burst in sessile oak (Quercus petraea).

Expression patterns of hundreds of transcripts in apical buds were monitored during bud flushing in sessile oak (Quercus petraea), in order to identify genes differentially expressed between the quiescent and active stage of bud development. Different transcriptomic techniques combining the construction of suppression subtractive hybridization (SSH) libraries and the monitoring of gene expression using macroarray and real-time reverse transcriptase polymerase chain reaction (RT-PCR) were performed to dissect bud burst, with a special emphasis on the onset of the process. We generated 801 expressed sequence tags (ESTs) derived from six developmental stages of bud burst. Macroarray experiment revealed a total of 233 unique transcripts exhibiting differential expression during the process, and a putative function was assigned to 65% of them. Cell rescue/defense-, metabolism-, protein synthesis-, cell cycle- and transcription-related transcripts were among the most regulated genes. Macroarray and real-time RT-PCR showed that several genes exhibited contrasted expressions between quiescent and swelling buds, such as a putative homologue of the transcription factor DAG2 (Dof Affecting Germination 2), previously reported to be involved in the control of seed germination in Arabidopsis thaliana. These differentially expressed genes constitute relevant candidates for signaling pathway of bud burst in trees.

Cluster Analysis↗
PubMed2005

Regulating the regulator: the control of auxin transport.

With the discovery of the phytohormone auxin in the late 1920s, it became possible to link the regulation of complex plant growth responses to a single biologically active compound. Among all the plant growth regulators characterised so far, only auxin appears to be actively transported throughout the plant to create complex variations in concentration patterns and flow directions over time. This stimulated interest in the specific mechanisms underlying auxin transport as key factors in plant growth responses. Research in the last decade revealed several genes involved in the controlled transport of auxin and greatly improved our understanding of the basic principles of auxin-mediated responses. We are at this point, however, only starting to understand the complex interplay and control of factors that ultimately underlie the observed spatiotemporal variations in auxin transport and thus mediate plant growth and environmental responses. This review highlights important findings that provide us with a framework of molecular players and potential regulatory mechanisms that should contribute to the formulation of a comprehensive dynamic model of spatiotemporal auxin distribution.

Biological Transport↗
PubMed2005

Functional redundancy of PIN proteins is accompanied by auxin-dependent cross-regulation of PIN expression.

Plant development displays an exceptional plasticity and adaptability that involves the dynamic, asymmetric distribution of the phytohormone auxin. Polar auxin flow, which requires polarly localized transport facilitators of the PIN family, largely contributes to the establishment and maintenance of the auxin gradients. Functionally overlapping action of PIN proteins mediates multiple developmental processes, including embryo formation, organ development and tropisms. Here we show that PIN proteins exhibit synergistic interactions, which involve cross-regulation of PIN gene expression in pin mutants or plants with inhibited auxin transport. Auxin itself positively feeds back on PIN gene expression in a tissue-specific manner through an AUX/IAA-dependent signalling pathway. This regulatory switch is indicative of a mechanism by which the loss of a specific PIN protein is compensated for by auxin-dependent ectopic expression of its homologues. The compensatory properties of the PIN-dependent transport network might enable the stabilization of auxin gradients and potentially contribute to the robustness of plant adaptive development.

Arabidopsis↗
PubMed2003

Detoxification of the Fusarium mycotoxin deoxynivalenol by a UDP-glucosyltransferase from Arabidopsis thaliana.

Plant pathogenic fungi of the genus Fusarium cause agriculturally important diseases of small grain cereals and maize. Trichothecenes are a class of mycotoxins produced by different Fusarium species that inhibit eukaryotic protein biosynthesis and presumably interfere with the expression of genes induced during the defense response of the plants. One of its members, deoxynivalenol, most likely acts as a virulence factor during fungal pathogenesis and frequently accumulates in grain to levels posing a threat to human and animal health. We report the isolation and characterization of a gene from Arabidopsis thaliana encoding a UDP-glycosyltransferase that is able to detoxify deoxynivalenol. The enzyme, previously assigned the identifier UGT73C5, catalyzes the transfer of glucose from UDP-glucose to the hydroxyl group at carbon 3 of deoxynivalenol. Using a wheat germ extract-coupled transcription/translation system we have shown that this enzymatic reaction inactivates the mycotoxin. This deoxynivalenol-glucosyltransferase (DOGT1) was also found to detoxify the acetylated derivative 15-acetyl-deoxynivalenol, whereas no protective activity was observed against the structurally similar nivalenol. Expression of the glucosyltransferase is developmentally regulated and induced by deoxynivalenol as well as salicylic acid, ethylene, and jasmonic acid. Constitutive overexpression in Arabidopsis leads to enhanced tolerance against deoxynivalenol.

Amino Acid Sequence↗
PubMed2003

PROPORZ1, a putative Arabidopsis transcriptional adaptor protein, mediates auxin and cytokinin signals in the control of cell proliferation.

Plants generate cells and organs throughout their life cycle. Plant cell proliferation relates to the activity of dividing meristematic cells, which subsequently differentiate in a position- and lineage-dependent manner. The events underlying the regulation of cell division and further differentiation processes are under tight control of both intrinsic and environmental parameters. Among the intrinsic factors, two groups of phytohormones, auxins and cytokinins, exhibit a combined regulatory impact on cell proliferation, as an important determinant for the totipotency of plant cells. Classical experiments demonstrated that application of both growth regulators in appropriate concentrations promotes callus formation. When the ratio between the phytohormones changes, callus cells acquire the competence to regenerate organs. Typically, a high auxin-to-cytokinin ratio promotes the formation of roots, whereas a low auxin-to-cytokinin ratio results in the regeneration of shoots. Conclusively, the concerted, proportional impact of both phytohormones functions as a determinant of plant cell proliferation; they act as cell cycle-promoting mitogens as well as morphogens that control plant organogenesis. Here, we describe PROPORZ1 (PRZ1), an Arabidopsis gene, essential for the developmental switch from cell proliferation to differentiation in response to variations in auxin and cytokinin concentrations. PRZ1 probably acts as a transcriptional adaptor protein that affects the expression of cell cycle regulators and might, thereby, mediate its effect on the control of cell proliferation.

Arabidopsis↗
PubMed2002

Auxin transport: ABC proteins join the club.

The isolation of potential auxin carriers from Arabidopsis thaliana marks a breakthrough in the characterization of elements involved in auxin delivery. Current models suggest that asymmetrical localization of auxin uptake and efflux carriers within the plasma membrane control the establishment of auxin gradients via facilitated transport. Now, the analysis of mutants defective in Arabidopsis ABC proteins indicates that primary active transport might participate in the control of auxin homeostasis as well.

ATP Binding Cassette Transporter, Subfamily B, Mem↗