The ubiquitin/26S proteasome proteolytic pathway selectively removes regulatory proteins, providing an efficient and rapid strategy to control many cellular processes and plays critical roles in protein removal in mammalian and plant cells. The proteasome is highly conserved and it has been shown that the bovine proteasome inhibitor 31 (PI31) and its homologues in mouse and humans diminish the activity of purified 20S proteasome; however, still little is known how proteasome activity is regulated in either mammals or plants. Through systemic genetics studies, we showed that an Arabidopsis homologue of the proteasome inhibitor PI31, which was designated as PROTEASOME REGULATOR1 (PTRE1), is a positive regulator of the 26S proteasome. Loss-of-function ptre1 mutant presents growth defect in multiple processes, and interesting, ptre1 is insensitive to auxinmediated suppression of proteasome activity. Further studies showed that auxin alters the subcellular localization of PTRE1, indicating this may be part of the mechanism by which it reduces proteasome activity and auxin regulates proteasome activity via PTRE1 to fine-tune the homoeostasis of Aux/IAA repressor proteins thus modifying auxin activity. Our further studies indicated that various factors modulate PTRE1 activity to involve the regulation of hormone signaling including gibberrllin and brassinotgeroids, and plant thermotolerance, which will be presented. As proteasome and whose activity control are involved in various developmental and stress-related processes, there should be possible links with the researches at different fields.