The Arabidopsis 26S proteasome subunit RPN1a is required for optimal plant growth and stress responses.

The current literature offers contradictory results regarding the role of the proteasome subunit RPN1a in Arabidopsis development. Here we show that plants lacking RPN1a are viable and have increased cell sizes, decreased heat shock tolerance, increased oxidative stress tolerance and other phenotypes characteristic for 26S proteasome subunit mutants. These results strengthen our contention that most of the phenotypes of 26S proteasome mutants in Arabidopsis described to date reflect a general impairment in 26S proteasome function rather than a specific defect of a single subunit, and suggest that the role of the RPN1a subunit during embryogenesis needs to be reconsidered.