E3 ubiquitin-protein ligase that mediates E2-dependent protein ubiquitination. Plays a role in salicylic acid-mediated negative feedback regulation of salicylic acid (SA) accumulation. May be involved in the overall regulation of SA, benzoic acid and phenylpropanoid biosynthesis. Involved in defense response. May act as negative regulator of resistance to the necrotrophic fungal pathogen Plectosphaerella cucumerina by modulating the accumulation of the phytoalexin camalexin and the salicylic acid- and jasmonate- dependent defense pathways. Controls the adaptability to nitrogen limitation by channeling the phenylpropanoid metabolic flux to the induced anthocyanin synthesis. Involved in the regulation of inorganic phosphate (Pi) homeostasis in a nitrate-dependent fashion. Directs the ubiquitination and subsequent degradation of the plasma membrane-localized inorganic phosphate transporters PHT1-1 and PHT1-4, to maintain phosphate homeostasis. The ubiquitination of PHTs triggers their clathrin-dependent endocytosis and trafficking to the vacuole through the endosomal pathway for degradation. Functions cooperatively with UBC24/PHO2 to regulate the abundance of PHT1-1, PHT1-2 and PHT1-3 in different subcellular compartments. Regulates Pi homeostasis by mediating, cooperatively with UBC24/PHO2, polyubiquitination of PHT1-4 and its targeting for degradation. Directs the polyubiquitination and subsequent degradation of the plasma membrane-localized nitrate transporter NPF2.13/NRT1.7, to help plants to adapt to nitrogen deficiency by regulating the source-to-sink remobilization of nitrate. Regulates leaf senescence during nitrogen deficiency by mediating, cooperatively with UBC24/PHO2, polyubiquitination of NAC92/ORE1 and its targeting for degradation