Plant diseases cause devastating crop losses around the world and threaten the food supply of millions of people. Over time, plants have developed powerful immune systems to resist infection by a wide range of pathogens. In the absence of pathogen threat, immune activators are kept under control by post- translational modifications including SUMOylation and ubiquitination. Activation of plant immunity is associated with large-scale transcriptional reprogramming induced by the unstable coactivator NPR1. I will discuss recent work showing that dynamic ubiquitination regulates the transcriptional activity of NPR1 during immune signalling and steps we are now taking to further understand the intricacies of this mechanism. I will also present work showing that pathogen-induced nitric oxide signalling directly impacts upon SUMOylation to promote immunity. These studies have demonstrated that ubiquitin and ubiquitin-like modifications are critical regulators of transcriptional responses in plant immunity. Finally, I will discuss how future research into ubiquitin-chain modifying enzymes in plants is critical to improve resistance against biotic and abiotic stresses.