ADDRESS: BUI TL, Cuu Long Delta Rice Research Institute, Cantho, Vietnam

e-mail: Bui Liem [liem.rice@gmail.com]

1. Constitutively expressed ERF-VII transcription factors redundantly activate the coreanaerobic response in Arabidopsis thaliana

Abstract:

Plant adaptation to hypoxic conditions is mediated by the transcriptional activation of genes involved in the metabolic reprogramming of plant cells to cope with reduced oxygen availability. Recent studies indicated that members of the group VII of the Ethylene Responsive Transcription Factor (ERFs) family act as positive regulators of this molecular response. In the current study, the five ERF-VII transcription factors of Arabidopsisthaliana were compared to infer a hierarchy in their role with respect to the anaerobic response. When the activity of each transcription factor was tested on a set of hypoxiaresponsive promoters, RAP2.2, RAP2.3 and RAP2.12 appeared to be the most powerful activators. RAP2.12 was further dissected in transactivation assays in Arabidopsis protoplasts to identify responsible regions for transcriptional activation. An ultimate Cterminal motif was identified as sufficient to drive gene transcription. Finally, using realtime RT-PCR in single and double mutants for the corresponding genes, we confirmed that RAP2.2 and RAP2.12 exert major control upon the anaerobic response.

2. Cross taxa analysis of the molecular response to low oxygen conditions in the plant kingdom

Abstract:

Plants adapt to environmental changes by evolutionary transformation not only in morphology physiology strategies but also genetic backgrounds. Low oxygen conditions occur often during a plant’s life cycle due to limitation of oxygen sources, such as during flooding, or high rate of its consumption. ERF-VII transcription factors are key players in regulation of low oxygen responses in Arabidopsis, where these proteins are substrates of the N-end rule pathway. Here, we present the evolutionary responses to low oxygen stress across plant taxa and the identification of roles of ERF-VII transcription factors, their homologs and enzyme components involves in the N-end rule pathway in different plant species. Our results reveal that ERF-VII transcription factors or homologs have been fixed only recently in fern species and maintained in higher plants whereas orthologues of the N-end rule enzymes are conserved in all plant species analyzed. Only spermatophytes displayed consistent upregulation of the genes identified previously as hypoxia responsive in monocots and dicots, whereas their orthologues in less evolved plant species showed fluctuations of these genes. Double mutation of two members ERF-VII RAP2.2 and RAP2.12 represses upregulation of anaerobic genes and overexpression of RAP2.12 could restore these gene responses under anoxia. Interestingly, overexpression of fern ERF homolog could only rescue Hb1 induction but not ADH and PDC in the same experiment. These findings indicate that the N-end rule is widely conserved in plant taxa and the ERF-VII evolved from recently vascular plant Pterisvitata and higher plants. In addition, evolutionary responses to low oxygen in Spermatophytes are consistent to monocot and dicots.