Biomedical subjects

Thomas Potuschak

Publications and source records attributed to Thomas Potuschak.

6 recordsLinked to original sources

PubMed2006

The exoribonuclease XRN4 is a component of the ethylene response pathway in Arabidopsis.

EXORIBONUCLEASE4 (XRN4), the Arabidopsis thaliana homolog of yeast XRN1, is involved in the degradation of several unstable mRNAs. Although a role for XRN4 in RNA silencing of certain transgenes has been reported, xrn4 mutant plants were found to lack any apparent visible phenotype. Here, we show that XRN4 is allelic to the unidentified components of the ethylene response pathway ETHYLENE-INSENSITIVE5/ACC-INSENSITIVE1 (EIN5/AIN1) and EIN7. xrn4 mutant seedlings are ethylene-insensitive as a consequence of the upregulation of EIN3 BINDING F-BOX PROTEIN1 (EBF1) and EBF2 mRNA levels, which encode related F-box proteins involved in the turnover of EIN3 protein, a crucial transcriptional regulator of the ethylene response pathway. Epistasis analysis placed XRN4/EIN5/AIN1 downstream of CTR1 and upstream of EBF1/2. XRN4 does not appear to regulate ethylene signaling via an RNA-INDUCED SILENCING COMPLEX-based RNA silencing mechanism but acts by independent means. The identification of XRN4 as an integral new component in ethylene signaling adds RNA degradation as another posttranscriptional process that modulates the perception of this plant hormone.

Alleles↗

PubMed2006

F-box proteins everywhere.

The ubiquitin proteasome system is a key regulator of many biological processes in all eukaryotes. This mechanism employs several types of enzymes, the most important of which are the ubiquitin E3 ligases that catalyse the attachment of polyubiquitin chains to target proteins for their subsequent degradation by the 26S proteasome. Among the E3 families, the SCF is the best understood; it consists of a multi-protein complex in which the F-box protein plays a crucial role by recruiting the target substrate. Strikingly, nearly 700 F-box proteins have been predicted in Arabidopsis, suggesting that plants have the capacity to assemble a multitude of SCF complexes, possibly controlling the stability of hundreds of substrates involved in a plethora of biological processes. Interestingly, viruses and even pathogenic bacteria have also found ways to hijack the plant SCF and to reprogram it for their own purposes.

F-Box Proteins↗

PubMed2005

Arabidopsis TCP20 links regulation of growth and cell division control pathways.

During postembryonic plant development, cell division is coupled to cell growth. There is a stringent requirement to couple these processes in shoot and root meristems. As cells pass through meristems, they transit through zones with high rates of cell growth and proliferation during organogenesis. This transition implies a need for coordinate regulation of genes underpinning these two fundamental cell functions. Here, we report a mechanism for coregulation of cell division control genes and cell growth effectors. We identified a GCCCR motif necessary and sufficient for high-level cyclin CYCB1;1 expression at G2/M. This motif is overrepresented in many ribosomal protein gene promoters and is required for high-level expression of the S27 and L24 ribosomal subunit genes we examined. p33(TCP20), encoded by the Arabidopsis TCP20 gene, binds to the GCCCR element in the promoters of cyclin CYCB1;1 and ribosomal protein genes in vitro and in vivo. We propose a model in which organ growth rates, and possibly shape in aerial organs, are regulated by the balance of positively and negatively acting teosinte-branched, cycloidea, PCNA factor (TCP) genes in the distal meristem boundary zone where cells become mitotically quiescent before expansion and differentiation.

Arabidopsis↗

PubMed2003

EIN3-dependent regulation of plant ethylene hormone signaling by two arabidopsis F box proteins: EBF1 and EBF2.

The plant hormone ethylene regulates a wide range of developmental processes and the response of plants to stress and pathogens. Genetic studies in Arabidopsis led to a partial elucidation of the mechanisms of ethylene action. Ethylene signal transduction initiates with ethylene binding at a family of ethylene receptors and terminates in a transcription cascade involving the EIN3/EIL and ERF families of plant-specific transcription factors. Here, we identify two Arabidopsis F box proteins called EBF1 and EBF2 that interact physically with EIN3/EIL transcription factors. EBF1 overexpression results in plants insensitive to ethylene. In contrast, plants carrying the ebf1 and ebf2 mutations display a constitutive ethylene response and accumulate the EIN3 protein in the absence of the hormone. Our work places EBF1 and EBF2 within the genetic framework of the ethylene-response pathway and supports a model in which ethylene action depends on EIN3 protein stabilization.

Arabidopsis↗

PubMed2003

PRT1 of Arabidopsis is a ubiquitin protein ligase of the plant N-end rule pathway with specificity for aromatic amino-terminal residues.

The gene PRT1 of Arabidopsis, encoding a 45-kD protein with two RING finger domains, is essential for the degradation of F-dihydrofolate reductase, a model substrate of the N-end rule pathway of protein degradation. We have determined the function of PRT1 by expression in yeast (Saccharomyces cerevisiae). PRT1 can act as a ubiquitin protein ligase in the heterologous host. The identified substrates of PRT1 have an aromatic residue at their amino-terminus, indicating that PRT1 mediates degradation of N-end rule substrates with aromatic termini but not of those with aliphatic or basic amino-termini. Expression of model substrates in mutant and wild-type plants confirmed this substrate specificity. A ligase activity exclusively devoted to aromatic amino-termini of the N-end rule pathway is apparently unique to plants. The results presented also imply that other known substrates of the plant N-end rule pathway are ubiquitylated by one or more different ubiquitin protein ligases.

Amino Acids, Aromatic↗

PubMed2002

The upstream Sal repeat-containing segment of Arabidopsis thaliana ribosomal DNA intergenic region (IGR) enhances the activity of adjacent protein-coding genes.

The sequence containing 'upstream Sal repeats' (USR) from the Arabidopsis thaliana ribosomal DNA intergenic region (IGR) was tested for its influence on the in vivo activity of nearby protein coding genes. On average, the presence of the IGR fragment leads to a four-fold increase in the expression of a reporter gene, beta-glucuronidase, under control of the strong CaMV 35S promoter. With the help of the site-specific cre-lox recombination system, we have also obtained pairs of transgenic lines with or without the USR-containing fragment, both integrated at the same chromosomal position. Results with these transgenic lines, which contain an NPT II (kanamycin resistance) gene under control of the nos promoter as a test gene, confirmed the results obtained with the CaMV 35S-driven GUS gene. Moreover, they show that the IGR sequence can oppose tendencies of gene silencing. We hypothesize that the described effect relates to features of the chromatin structure in the proximity of the upstream Sal repeats.

Arabidopsis↗