PUB - Publikationen an der Universität Bielefeld

Flooding impairs plant growth through oxygen deprivation, which activates plant survival and acclimation responses. Transcriptional responses to low oxygen are generally associated with the activation of group VII ETHYLENE‐RESPONSE FACTOR (ERFVII) transcription factors. However, the exact mechanisms and molecular components by which ERFVII factors initiate gene expression are not fully elucidated. Here, we show that the ERFVII factors RELATED TO APETALA 2.2 (RAP2.2) and RAP2.12 cooperate with the Mediator complex subunit At MED25 to coordinate gene expression under hypoxia in Arabidopsis thaliana . Respective med25 knock‐out mutants display reduced low‐oxygen stress tolerance. At MED25 physically associates with a distinct set of hypoxia core genes and its loss partially impairs transcription under hypoxia due to decreased RNA polymerase II recruitment. Association of At MED25 with target genes requires the presence of ERFVII transcription factors. Next to ERFVII protein stabilisation, also the composition of the Mediator complex including At MED25 is potentially affected by hypoxia stress as shown by protein‐complex pulldown assays. The dynamic response of the Mediator complex to hypoxia is furthermore supported by the fact that two subunits, At MED8 and At MED16, are not involved in the establishment of hypoxia tolerance, whilst both act in coordination with At MED25 under other environmental conditions. We furthermore show that At MED25 function under hypoxia is independent of ethylene signalling. Finally, functional conservation at the molecular level was found for the MED25‐ERFVII module between A. thaliana and the monocot species Oryza sativa , pointing to a potentially universal role of MED25 in coordinating ERFVII‐dependent transcript responses to hypoxia in plants.