Oxidative and Salt Stresses Alter the 26S Proteasome Holoenzyme and Associated Protein Profiles in Arabidopsis Thaliana

Abstract

Background: The 26S proteasome, canonically composed of multi-subunit 19S regulatory (RP) and 20S core (CP) particles, is crucial for cellular proteostasis. Proteasomes may be re-modeled, activated, or re-localized and this regulation is critical for plants in response to environmental stresses. The proteasome holoenzyme assembly and dissociation are therefore highly dynamic in vivo. However, the stoichiometric changes of the plant proteasomes and how proteasome associated chaperones vary under common abiotic stresses have not been systematically studied.Results: Here, we studied the impact of abiotic stresses on proteasome structure, activity, and interacting partners in Arabidopsis thaliana. We analyzed available RNA expression data and observed that expressions of proteasome coding genes varied substantially under stresses; however, the protein levels of a few key subunits did not change significantly within 24 hours. Instead, a switch in the predominant proteasome complex, from 26S to 20S, occurs under oxidative or salt stress. Oxidative stress also reduced the cellular ATP content and the association of HSP70-family proteins to the 20S proteasome, but enhanced the activity of cellular free form CP. Salt stress, on the other hand, did not affect cellular ATP level, but caused subtle changes in proteasome subunit composition and impacted bindings of assembly chaperones. Analyses of an array of T-DNA insertional mutant lines highlighted important roles for several putative assembly chaperones in seedling establishment and stress sensitivity. We also observed that knockout of PBAC1, one of the a-ring assembly chaperones, resulted in hypersensitivity and tearing of the seed coat during sterilization. Conclusions: Our study revealed an evolutionarily conserved mechanism of proteasome regulation during oxidative stress, involving dynamic regulation of the holoenzyme formation and associated regulatory proteins, and we also identified a novel role of the PBAC1 proteasome assembly chaperone in seed coat development.

Proteasomal activity is differentially regulated in source and sink tissues of Arabidopsis

“…Especially DC and SC 26S proteasome activity in ageing siliques increased while 20S activity appeared to remain unaffected. Of note, 20S activity bands of the siliques (20S +) run higher in the gel as compared to those in leaves, suggesting the presence of chaperones or other proteins interacting with the core particle in siliques (Bonea et al, 2021).…”