Abstract
The plant hormone auxin is perceived by the nuclear F-box protein TIR1 receptor family and regulates gene expression through degradation of Aux/IAA transcriptional repressors. Several studies have revealed the importance of the proteasome in auxin signalling, but details on how the proteolytic machinery is regulated and how this relates to degradation of Aux/IAA proteins remains unclear. Here we show that an Arabidopsis homologue of the proteasome inhibitor PI31, which we name PROTEASOME REGULATOR1 (PTRE1), is a positive regulator of the 26S proteasome. Loss-of-function ptre1 mutants are insensitive to auxin-mediated suppression of proteasome activity, show diminished auxin-induced degradation of Aux/IAA proteins and display auxin-related phenotypes. We found that auxin alters the subcellular localization of PTRE1, suggesting this may be part of the mechanism by which it reduces proteasome activity. Based on these results, we propose that auxin regulates proteasome activity via PTRE1 to fine-tune the homoeostasis of Aux/IAA repressor proteins thus modifying auxin activity.
Highlights
The plant hormone auxin is perceived by the nuclear F-box protein TRANSPORT INHIBITOR RESPONSE 1 (TIR1) receptor family and regulates gene expression through degradation of Aux/IAA transcriptional repressors
The F-box protein TRANSPORT INHIBITOR RESPONSE 1 (TIR1) receptor family regulates the transcription of auxin-dependent genes by stimulating degradation of Aux/IAA proteins[2,3], suggesting the proteasome plays a crucial role in regulating Aux/IAA homoeostasis and downstream auxin signalling[4]
We identified a protein encoding a 302 amino acid polypeptide that shares high homology with mammalian proteasome inhibitor 31 (PI31), which we designated as PROTEASOME REGULATOR1, (PTRE1)
Summary
The plant hormone auxin is perceived by the nuclear F-box protein TIR1 receptor family and regulates gene expression through degradation of Aux/IAA transcriptional repressors. Several studies have revealed the importance of the proteasome in auxin signalling, but details on how the proteolytic machinery is regulated and how this relates to degradation of Aux/IAA proteins remains unclear. The F-box protein TRANSPORT INHIBITOR RESPONSE 1 (TIR1) receptor family regulates the transcription of auxin-dependent genes by stimulating degradation of Aux/IAA proteins[2,3], suggesting the proteasome plays a crucial role in regulating Aux/IAA homoeostasis and downstream auxin signalling[4]. PTRE1 stimulates 26S proteasome activity and influences auxinrelated processes during plant growth and development We propose that it acts in concert with the TIR1-AFB pathway to buffer the degradation of Aux/IAA proteins and modulate the expression of auxin-responsive genes in a precise manner
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