Characterization of the hypoxia-induced transcription factor ABR1

Judith Bäumler1, Angelika Mustroph1
1 Plant Genetics, University of Bayreuth

P 1.1 in Special SPECIES and species' specialties

Plants can suffer from low oxygen stress (hypoxia), for example during root submergence or waterlogging, and respond to it by a variety of transcriptomic changes. In Arabidopsis thaliana major regulators of the hypoxic response are the group VII ERF transcription factors: they accumulate under hypoxic conditions to initiate the transcription of hypoxia-responsive genes and are degraded under normoxic conditions. Because of the fact that their stability is dependent on its N-Terminus, the underlying mechanism is called the N-end rule pathway (NERP).

We are interested in the function of the transcription factor ABSCISIC ACID REPRESSOR 1 (ABR1) that seems to be highly induced by hypoxia. According to its title, a previous study suggested a role in abscisic acid signalling, which could not be confirmed by our data. Interestingly, ABR1 contains the conserved N-terminal methionine/cysteine (MC) motif, which makes it a possible target for the NERP. ABR1-overexpression lines showed multiple phenotypes: 5-week-old plants possessed smaller rosette leaves and shorter petioles in comparison to the wildtype, whereas seedlings formed a lot of root hairs, whose formation seemed to correlate with the ABR1 transcript level. As a first approach to investigate this phenotype, we analyzed the cell patterning of the root epidermis and observed that root hairs are not only produced in root hair cells, but also in the so-called non-hair cells, that normally lack root hairs. To provide an informative basis, we performed a microarray analysis of ABR1-overexpressing plants. Right now we are trying to link the expression data to the observed phenotypes. First evaluations of the microarray experiment connected a major part of the genes differentially regulated by an ABR1-overexpression to abiotic and biotic stress. By using a glucocorticoid-inducible protoplast assay we plan to confirm this assumption and furthermore try to detect direct target genes of ABR1.

Keywords: Arabidopsis thaliana, root hairs, hypoxia, N-end rule pathway, microarray
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