Autophagic substrate degraded in the vacuole by non-selective autophagy. Requires ATG8 protein expression to be recognized as an autophagic substrate (PubMed:21606687). Acts probably as a receptor for autophagosomal degradation of ubiquitinated proteins. Targets ubiquitinated protein aggregates derived from denatured or damaged non-native proteins generated under stress conditions (PubMed:23341779). Functions additively with the E3 ubiquitin-protein ligase CHIP for autophagosomal degradation of proteotoxic aggregates formed under stress conditions (PubMed:24497840). Homodimer. Interacts with ATG8A, ATG8B, ATG8C, ATG8D, ATG8F and ATG8I. Binds to ubiquitin. Forms large punctated cytoplasmic structures. Recruited to the central vacuole by non-selective autophagy. By heat shock. The PB1 domain mediates homodimerization. The UBA domain is required for ubiquitin binding. The LIR motif is required for the interaction with ATG8 proteins and for vacuolar import (PubMed:21606687). The LIR motif is required for NBR1 function as receptor for autophagosomal degradation of ubiquitinated proteins under stress conditions (PubMed:23341779). No visible phenotype under normal growth conditions, but mutant plants show enhanced sensitivity to heat, oxidative, salt, and drought stresses.