MEDIATOR SUBUNIT 25 modulates ERFVII-controlled hypoxia responses in Arabidopsis

Flooding impairs plant growth through oxygen deprivation, which activates plant survival and acclimation responses. Low-oxygen responses are generally associated with activation of group VII ETHYLENE-RESPONSE FACTOR (ERFVII) transcription factors. However, mechanism and molecular components by which ERFVII factors initiate gene expression are not fully elucidated. Here, we show that the Mediator complex subunit At MED25 is recruited by RELATED TO APETALA 2.2 (RAP2.2) and RAP2.12 to coordinate gene expression during hypoxia in Arabidopsis thaliana .. The med25 mutants display reduced low-oxygen stress tolerance. At MED25 associates with several ERFVII-controlled hypoxia core genes and its loss impairs transcription under hypoxia due to decreasing RNA polymerase II recruitment. Protein complex pulldown assays demonstrate that the Mediator complex built around At MED25 is adjusted under low-oxygen conditions. Moreover, during hypoxia, no functional cooperation between At MED25 and the two subunits At MED8 and At MED16 occurs, contrasting previous observations made for other conditions. In addition, At MED25 function under hypoxia is independent from ethylene signalling. Finally, a functional conservation at the molecular level was found for the MED25-ERFVII module between Arabidopsis thaliana and the monocot Oryza sativa , pointing to a potentially universal role of MED25 in enabling ERFVII-dependent transcript responses to hypoxia in plants.