Plant PRC2 subunit VRN2 stability regulation through oxygen dependent proteolysis

Polycomb repressive complex 2 (PRC2) represses the expression of its gene targets epigenetically and VERNALIZATION 2 (VRN2) is a subunit of the PRC2 complex in Arabidopsis. The PRC2-VRN2 complex, among other roles, regulates flowering after long cold exposure. Gibbs and coworkers identified VRN2 as a possible target for the N end rule pathway, since it posses a conserved Met-Cys (MC-) N terminal. The N-end rule regulates protein destruction by ubiquitylation with specific E3 ligases of the N terminal (N-) degron. Using the PRT6 E3-ligase mutant and an Ala-VRN2 mutated version they could show that the N-end rule pathway indeed regulates VRN2 under non stressing conditions, keeping it only in meristematic tissues. Further studies also showed that VRN2 is stabilized through the plant by low levels of O₂ and contributes to hypoxia resistance. Experiments with the VRN2 barley homolog also showed a functional N-degron. Phylogenetic analysis of other VRN2 plant homologs suggested that this mechanism appeared early in angiosperm evolution, linking PRC2 epigenetic activity to environmental conditions. (Summary by Cecilia Vasquez Robinet) Nature Comms. 10.1038/s41467-018-07875-7