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Publikationen - Molekulare Signalverarbeitung

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Publikation

Schwager, K. M.; Calderon-Villalobos, L. I. A.; Dohmann, E. M.; Willige, B. C.; Knierer, S.; Nill, C.; Schwechheimer, C.; Characterization of the VIER F-BOX PROTEINE Genes from Arabidopsis Reveals Their Importance for Plant Growth and Development Plant Cell 19, 1163-1178, (2007) DOI: 10.1105/tpc.105.040675

E3 ubiquitin ligases (E3s) target proteins for degradation by the 26S proteasome. In SKP1/CDC53/F-box protein–type E3s, substrate specificity is conferred by the interchangeable F-box protein subunit. The vast majority of the 694 F-box proteins encoded by the Arabidopsis thaliana genome remain to be understood. We characterize the VIER F-BOX PROTEINE (VFB; German for FOUR F-BOX PROTEINS) genes from Arabidopsis that belong to subfamily C of the Arabidopsis F-box protein superfamily. This subfamily also includes the F-box proteins TRANSPORT INHIBITOR RESPONSE1 (TIR1)/AUXIN SIGNALING F-BOX (AFB) proteins and EIN3 BINDING F-BOX proteins, which regulate auxin and ethylene responses, respectively. We show that loss of VFB function causes delayed plant growth and reduced lateral root formation. We find that the expression of a number of auxin-responsive genes and the activity of DR5:β-glucuronidase, a reporter for auxin reponse, are reduced in the vfb mutants. This finding correlates with an increase in the abundance of an AUXIN/INDOLE-3-ACETIC ACID repressor. However, we also find that auxin responses are not affected in the vfb mutants and that a representative VFB family member, VFB2, cannot functionally complement the tir1-1 mutant. We therefore exclude the possibility that VFBs are functional orthologs of TIR1/AFB proteins.
Publikation

Vigliocco, A.; Alemano, S.; Miersch, O.; Alvarez, D.; Abdala, G.; Endogenous jasmonates in dry and imbibed sunflower seeds from plants grown at different soil moisture contents Seed Sci. Res. 17, 91-98, (2007) DOI: 10.1017/S0960258507708371

In this study, we characterized two sunflower (Helianthus annuus L.) lines with differential sensitivity to drought, the sensitive line B59 and the tolerant line B71. Using both lines, we compared the content of endogenous jasmonates (JAs) in dry and imbibed seeds from plants grown under irrigation and drought. Jasmonic acid (JA), 12-oxo-phytodienoic acid (OPDA), 11-hydroxyjasmonate (11-OH-JA) and 12-hydroxyjasmonate (12-OH-JA) were detected in dry and imbibed sunflower seeds. Seeds from plants grown under drought had a lower content of total JAs and exhibited higher germination percentages than seeds from irrigated plants, demonstrating that environmental conditions have a strong influence on the progeny. OPDA and 12-OH-JA were the main compounds found in dry seeds of both lines. Imbibed seeds showed an enhanced amount of total JAs with respect to dry seeds produced by plants grown in both soil moisture conditions. Imbibition triggered a dramatic OPDA increase in the embryo, suggesting a role of this compound in germination. We conclude that JAs patterns vary during sunflower germination and that the environmental conditions experienced by the mother plant modify the hormonal content of the seed progeny.
Publikation

Abel, S.; Auxin Is Surfacing ACS Chem. Biol. 2, 380-384, (2007) DOI: 10.1021/cb7001158

Indole-3-acetic acid (IAA or auxin) is essential throughout the life cycle of a plant. It controls diverse cellular processes, including gene expression. The hormone is perceived by a ubiquitin protein ligase (E3) and triggers the rapid destruction of repressors, called Aux/IAA proteins. The first structural model of a plant hormone receptor illustrates how auxin promotes Aux/IAA substrate recruitment by extending the hydrophobic protein-interaction surface. This work establishes a novel mechanism of E3 regulation by small molecules and promises a novel strategy for the treatment of human disorders associated with defective ubiquitin-dependent proteolysis.
Publikation

Calderon-Villalobos, L. I. A.; Nill, C.; Marrocco, K.; Kretsch, T.; Schwechheimer, C.; The evolutionarily conserved Arabidopsis thaliana F-box protein AtFBP7 is required for efficient translation during temperature stress Gene 392, 106-116, (2007) DOI: 10.1016/j.gene.2006.11.016

In eukaryotes, E3 ubiquitin ligases (E3s) mediate the ubiquitylation of proteins that are destined for degradation by the ubiquitin–proteasome system. In SKP1/CDC53/F-box protein (SCF)-type E3 complexes, the interchangeable F-box protein confers specificity to the E3 ligase through direct physical interactions with the degradation substrate. The vast majority of the approximately 700 F-box proteins from the plant model organism Arabidopsis thaliana remain to be characterized. Here, we investigate the previously uncharacterized and evolutionarily conserved Arabidopsis F-box protein 7 (AtFBP7), which is encoded by a unique gene in Arabidopsis (At1g21760). Several apparent fbp7 loss-of-function alleles do not have an obvious phenotype. AtFBP7 is ubiquitously expressed and its expression is induced after cold and heat stress. When following up on a reported co-purification of the eukaryotic elongation factor-2 (eEF-2) with YLR097c, the apparent budding yeast orthologue of AtFBP7, we discovered a general defect in protein biosynthesis after cold and heat stress in fbp7 mutants. Thus, our findings suggest that AtFBP7 is required for protein synthesis during temperature stress.
Publikation

Abel, S.; Ticconi, C. A.; Delatorre, C. A.; Phosphate sensing in higher plants Physiol. Plant. 115, 1-8, (2002) DOI: 10.1034/j.1399-3054.2002.1150101.x

Phosphate (Pi) plays a central role as reactant and effector molecule in plant cell metabolism. However, Pi is the least accessible macronutrient in many ecosystems and its low availability often limits plant growth. Plants have evolved an array of molecular and morphological adaptations to cope with Pi limitation, which include dramatic changes in gene expression and root development to facilitate Pi acquisition and recycling. Although physiological responses to Pi starvation have been increasingly studied and understood, the initial molecular events that monitor and transmit information on external and internal Pi status remain to be elucidated in plants. This review summarizes molecular and developmental Pi starvation responses of higher plants and the evidence for coordinated regulation of gene expression, followed by a discussion of the potential involvement of plant hormones in Pi sensing and of molecular genetic approaches to elucidate plant signalling of low Pi availability. Complementary genetic strategies in Arabidopsis thaliana have been developed that are expected to identify components of plant signal transduction pathways involved in Pi sensing. Innovative screening methods utilize reporter gene constructs, conditional growth on organophosphates and the inhibitory properties of the Pi analogue phosphite, which hold the promise for significant advances in our understanding of the complex mechanisms by which plants regulate Pi‐starvation responses.
Publikation

Wang, Q.; Grubb, C. D.; Abel, S.; Direct analysis of single leaf disks for chemopreventive glucosinolates Phytochem. Anal. 13, 152-157, (2002) DOI: 10.1002/pca.636

Natural isothiocyanates, produced during plant tissue damage from methionine‐derived glucosinolates, are potent inducers of mammalian phase 2 detoxification enzymes such as quinone reductase (QR). A greatly simplified bioassay for glucosinolates based on induction and colorimetric detection of QR activity in murine hepatoma cells is described. It is demonstrated that excised leaf disks of Arabidopsis thaliana (ecotype Columbia) can directly and reproducibly substitute for cell‐free leaf extracts as inducers of murine QR, which reduces sample preparation to a minimum and maximizes throughput. A comparison of 1 and 3 mm diameter leaf disks indicated that QR inducer potency was proportional to disk circumference (extent of tissue damage) rather than to area. When compared to the QR inducer potency of the corresponding amount of extract, 1 mm leaf disks were equally effective, whereas 3 mm disks were 70% as potent. The QR inducer potency of leaf disks correlated positively with the content of methionine‐derived glucosinolates, as shown by the analysis of wild‐type plants and mutant lines with lower or higher glucosinolate content. Thus, the microtitre plate‐based assay of single leaf disks provides a robust and inexpensive visual method for rapidly screening large numbers of plants in mapping populations or mutant collections and may be applicable to other glucosinolate‐producing species.
Publikation

Vigliocco, A.; Bonamico, B.; Alemano, S.; Miersch, O.; Abdala, G.; Stimulation of jasmonic acid production in Zea Mays L. infected by the maize rough dwarf virus - Río Cuarto. Reversion of symptoms by salicylic acid Biocell 26, 369-374, (2002)

In the present paper we study the possible biological relevance of endogenous jasmonic acid (JA) and exogenous salicylic acid (SA) in a plant-microbial system maize-virus. The virus disease "Mal de Río Cuarto" is caused by the maize rough dwarf virus - Río Cuarto. The characteristic symptoms are the appearance of galls or "enations" in leaves, shortening of the stem internodes, poor radical system and general stunting. Changes in JA and protein pattern in maize control and infected plants of a virus-tolerant cultivar were investigated. Healthy and infected-leaf discs were collected for JA measurement at different post-infection times (20, 40, 60 and 68 days). JA was also measured in roots on day 60 after infection. For SDS-PAGE protein analysis, leaf discs were also harvested on day 60 after infection. Infected leaves showed higher levels of JA than healthy leaves, and the rise in endogenous JA coincided with the enation formation. The soluble protein amount did not show differences between infected and healthy leaves; moreover, no difference in the expression of soluble protein was revealed by SDS-PAGE. Our results show that the octadecanoid pathway was stimulated in leaves and roots of the tolerant maize cultivar when infected by this virus. This finding, together with fewer plants with the disease symptoms, suggest that higher foliar and roots JA content may be related to disease tolerance. SA exogenous treatment caused the reversion of the dwarfism symptom.
Publikation

Laskowski, M. J.; Dreher, K. A.; Gehring, M. A.; Abel, S.; Gensler, A. L.; Sussex, I. M.; FQR1, a Novel Primary Auxin-Response Gene, Encodes a Flavin Mononucleotide-Binding Quinone Reductase Plant Physiol. 128, 578-590, (2002) DOI: 10.1104/pp.010581

FQR1 is a novel primary auxin-response gene that codes for a flavin mononucleotide-binding flavodoxin-like quinone reductase. Accumulation of FQR1 mRNA begins within 10 min of indole-3-acetic acid application and reaches a maximum of approximately 10-fold induction 30 min after treatment. This increase in FQR1 mRNA abundance is not diminished by the protein synthesis inhibitor cycloheximide, demonstrating thatFQR1 is a primary auxin-response gene. Sequence analysis reveals that FQR1 belongs to a family of flavin mononucleotide-binding quinone reductases. Partially purified His-tagged FQR1 isolated fromEscherichia coli catalyzes the transfer of electrons from NADH and NADPH to several substrates and exhibits in vitro quinone reductase activity. Overexpression of FQR1 in plants leads to increased levels of FQR1 protein and quinone reductase activity, indicating that FQR1 functions as a quinone reductase in vivo. In mammalian systems, glutathione S-transferases and quinone reductases are classified as phase II detoxification enzymes. We hypothesize that the auxin-inducible glutathioneS-transferases and quinone reductases found in plants also act as detoxification enzymes, possibly to protect against auxin-induced oxidative stress.
Publikation

Grubb, C. D.; Gross, H. B.; Chen, D. L.; Abel, S.; Identification of Arabidopsis mutants with altered glucosinolate profiles based on isothiocyanate bioactivity Plant Sci. 162, 143-152, (2002) DOI: 10.1016/S0168-9452(01)00550-7

Glucosinolates are a diverse class of nitrogen- and sulfur-containing secondary metabolites. They are rapidly hydrolyzed on tissue disruption to a number of biologically active compounds that are increasingly attracting interest as anticarcinogenic phytochemicals and crop protectants. Several glucosinolate-derived isothiocyanates are potent chemopreventive agents that favorably modulate carcinogen metabolism in mammals. Methylsulfinylalkyl isothiocyanates, in particular the 4-methylsulfinylbutyl derivative, are selective and potent inducers of mammalian detoxification enzymes such as quinone reductase (QR). Cruciferous plants including Arabidopsis thaliana (L.) Heyhn, synthesize methylsulfinylalkyl glucosinolates, which are derived from methionine. Using a colorimetric assay for QR activity in murine hepatoma cells and high performance liquid chromatography (HPLC) analysis of desulfoglucosinolates, we have demonstrated a strong positive correlation between leaf QR inducer potency and leaf content of methionine-derived glucosinolates in various A. thaliana ecotypes and available glucosinolate mutants. In a molecular genetic approach to glucosinolate biosynthesis, we screened 3000 chemically mutagenized M2 plants of the Columbia ecotype for altered leaf QR inducer potency. Subsequent HPLC analysis of progeny of putative mutants identified six lines with significant and heritable changes in leaf glucosinolate content and composition.
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