| Summary: | All aerobic organisms require O2 for survival. When their O2 is limited (hypoxia), a response is required to reduce demand and/or improve supply. A hypoxic response mechanism has been identified in flowering plants: stability of proteins with N-terminal cysteine residues is regulated in an O2-dependent manner by the Cys/Arg branch of the N-degron pathway. Oxidation of these cysteine residues is catalysed by plant cysteine oxidases (PCOs) which destabilises proteins in normoxia; PCO inactivity in hypoxia results in protein stabilisation. Biochemically, the PCOs are sensitive to O2 availability and can therefore act as plant O2 sensors and regulation of the stability of proteins such as Group VII ethylene response factors (ERF-VIIs) can initiate adaptive responses to hypoxia. It is not known whether oxygen-sensing mechanisms exist in other phyla from the plant kingdom. Known PCO targets are only conserved in flowering plants, however PCO-like sequences are conserved in all planta. We sought to determine whether PCO-like enzymes from the liverwort, Marchantia polymorpha (MpPCO) and the freshwater algae, Klebsormidium nitens (KnPCO) have a similar function to PCO enzymes from Arabidopsis thaliana . We report that MpPCO and KnPCO show O2-sensitive N-terminal cysteine dioxygenase activity towards known AtPCO ERF-VII substrates as well as a putative endogenous substrate, MpERF-like, which was identified by homology to the Arabidopsis ERF-VIIs transcription factors. This work confirms functional and O2-dependent PCOs from Bryophyta and Charophyta, indicating the potential for PCO-mediated O2-sensing pathways in these organisms and suggesting PCO O2-sensing function could be important throughout the plant kingdom.
|
|---|