Journal Article

Proteasome-associated HECT-type ubiquitin ligase activity is required for plant immunity

Grey, Heather, Spoel, Steven H., Wang, Zhishuo, Nomoto, Mika, Furniss, James J., Jackson, Lorna, Tada, Yasuomi

2018

Overview

Regulated degradation of proteins by the 26S proteasome plays important roles in maintenance and signalling in eukaryotic cells. Proteins are marked for degradation by the action of E3 ligases that site-specifically modify their substrates by adding chains of ubiquitin. Innate immune signalling in plants is deeply reliant on the ubiquitin-26S proteasome system. While progress has been made in understanding substrate ubiquitination during plant immunity, how these substrates are processed upon arrival at the proteasome remains unclear. Here we show that specific members of the HECT domain-containing family of ubiquitin protein ligases (UPL) play important roles in proteasomal substrate processing during plant immunity. Mutations in UPL1, UPL3 and UPL5 significantly diminished immune responses activated by the immune hormone salicylic acid (SA). In depth analyses of upl3 mutants indicated that these plants were impaired in reprogramming of nearly the entire SA-induced transcriptome and failed to establish immunity against a hemi-biotrophic pathogen. UPL3 was found to physically interact with the regulatory particle of the proteasome and with other ubiquitin-26S proteasome pathway components. In agreement, we demonstrate that UPL3 enabled proteasomes to form polyubiquitin chains, thereby regulating total cellular polyubiquitination levels. Taken together, our findings suggest that proteasome-associated ubiquitin ligase activity of UPL3 promotes proteasomal processivity and is indispensable for development of plant immunity.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Arabidopsis - genetics / Arabidopsis - metabolism / Arabidopsis Proteins - genetics / Arabidopsis Proteins - metabolism / Binding sites / Biodegradation / Biology and Life Sciences / Chains / Degradation / Enzymes / Eukaryotes / Gene expression / Genomes / Hormones / Immune response / Immunity / Ligases / Ligases - genetics / Ligases - metabolism / Medicine and Health Sciences / Mutants / Mutation / Phenols (Class of compounds) / Plant immunity / Plant Immunity - immunology / Plant Immunity - physiology / Polyubiquitin - genetics / Proteasome 26S / Proteasome Endopeptidase Complex - genetics / Proteasome Endopeptidase Complex - metabolism / Proteasomes / Proteins / Proteolysis / Salicylic acid / Salicylic Acid - metabolism / Signal transduction / Signaling / Substrates / Ubiquitin / Ubiquitin - metabolism / Ubiquitin-proteasome system / Ubiquitin-protein ligase / Ubiquitin-Protein Ligase Complexes - genetics / Ubiquitin-Protein Ligase Complexes - metabolism / Ubiquitin-Protein Ligases - metabolism / Ubiquitination