Transcriptional control of the response of Arabidopsis thaliana to hypoxic stress
Final Report Abstract
Plants can be exposed to periods of low-oxygen concentrations, for example during flooding events, but also in plant organs with densely packed cells. Under those stress conditions, mitochondrial respiration is strongly inhibited, leading to reduced ATP production and a subsequent energy crisis inside plant cells. In order to cope with this stress, plants have evolved multiple adaptational mechanisms, for example morphological changes to outgrow the flooded soil (leaf elongation, aerenchyma formation), or biochemical modifications. A major biochemical response found in sensitive and tolerant species is the induction of the fermentative enzymes alcohol dehydrogenase and pyruvate decarboxylase in order to maintain at least the glycolytic flux and therefore glycolytic ATP production under oxygen deficiency stress. The transcriptional regulation of those processes has been revealed only recently. The goal of our project was the elucidation of transcription factors that regulate the induction of genes under oxygen deficiency stress. For this, the promoter of a strong and conserved hypoxia-inducible gene LOB DOMAIN-CONTAINING PROTEIN 41 (LBD41) was chosen and analyzed in a protoplast transactivation system with a library of Arabidopsis transcription factors. Several activators were found in this system, among them all members of the subgroup VII of the ETHYLENE RESPONSE FACTOR (ERF) transcription factors. During our screen, other groups discovered those ERF transcription factors as the major regulators of hypoxic gene induction, which was a major break-through in our research field. They also described the mechanism with which plants can respond to a decrease in oxygen concentrations - based on the oxygen-dependent degradation of group VII ERF proteins through the N-end rule pathway. Due to the appearance of the publications, we extended our screen to the search for repressing transcription factors of the low-oxygen-inducible promoter with the same library. This screen revealed several interesting candidates that provide a basis for still ongoing research. As a second goal, we wanted to identify the responsive promoter element for the group VII ERF transcription factors. With the help of the protoplast transactivation system we were able to identify a 33-bp-element that was sufficient and necessary for the induction of the LBD41- promoter by group VII ERFs as well as oxygen deficiency. This element was confirmed by yeast-1-hybrid experiments and Chromatin immunoprecipitation. Furthermore, with a newly developed phylogenetic footprinting pipeline on conserved hypoxia-responsive genes we were able to bioinformatically predict the binding element found above, another confirmation of the results from the protoplast transactivation system.
Publications
- (2011) Plant oxygen sensing is mediated by the N-end rule pathway: a milestone in plant anaerobiosis. Plant Cell 23: 4173-4183
Sasidharan R, Mustroph A
- (2014) A shoot-specific hypoxic response of Arabidopsis thaliana sheds light on the role of the phosphate-responsive transcription factor PHR1. Plant Physiol 165: 774-790
Klecker M, Gasch P, Peisker H, Dörmann P, Schlicke H, Grimm B, Mustroph A
(See online at https://doi.org/10.1038/nphoton.2014.48) - (2015) Redundant ERF-VII transcription factors bind to an evolutionarily-conserved cis-motif to regulate hypoxia-responsive gene expression in Arabidopsis. Plant Cell (PDF: 66 S.)
Gasch P, Fundinger M, Müller JT, Lee T, Bailey-Serres J, Mustroph A
(See online at https://doi.org/10.1105/tpc.15.00866)
