Characterization of the Arabidopsis thaliana homologue of NBR1

Abstract

It is now well established that p62 and NBR1 are selectively degraded by autophagy and can act as cargo receptors or adaptors for the autophagic degradation of ubiquitinated substrates. Research on autophagy in plants is also well under way, but the mechanism by which target substrates are sequestered for autophagic degradation has not been elucidated. The uncharacterized plant protein Q9SB64 shares several important functional properties with p62 and NBR1, which indicates that it could act as a cargo receptor for the autophagic degradation of ubiquitinated substrates in plants. Results from this study show that Q9SB64 polymerize via an N-terminal PB1 domain, binds ubiquitin through a C-terminal UBA domain and interacts with the Arabidopsis family of ATG8 proteins. Based on sequence similarity Q9SB64 can be viewed as the Arabidopsis orthologue of vertebrate NBR1 and named AtNBR1. Plants do not seem to have a p62 orthologue. However, with regard to the functional properties studied here AtNBR1 behaves more similar to mammalian p62 than to NBR1.