Auxin plays crucial roles in regulating plant growth and development. Previous studies have demonstrated that auxin transduces its signal by promoting the proteolysis of transcriptional repressor Aux/IAAs by the 26S proteasome. However, regulatory mechanism of the homeostasis of Aux/IAA proteins remains unclear.  

Now, Prof. XUE Hongwei and his colleagues at the Institute of Plant Physiology and Ecology (SIPPE) of Shanghai Institutes for Biological Sciences identified a new player, named PROTEASOME REGULATOR1 (PTRE1), in auxin signaling pathway.  

PTRE1 encodes an Arabidopsis homolog of the mammalian proteasome inhibitor PI31 and acts as a positive regulator for auxin-mediated regulation of proteasome activity. Loss-of-function ptre1 mutants display auxin-related phenotypes, are insensitive to auxin-mediated suppression of proteasome activity, and show diminished auxin-induced degradation of Aux/IAA proteins. More interestingly, auxin may suppress proteasome activity through altering the subcellular localization of PTRE1.  

Proteasome-mediated protein degradation involves in various aspects of hormone signaling and stress responses. This study helps to understand how auxin regulates proteasome activity, as well as the functional mechanism of auxin and other plant hormones.  

This study entitled “ArabidopsisPROTEASOME REGULATOR1 is required for auxin-mediated suppression of proteasome activity and regulates auxin signaling” was published online in Nature Communications on April 25^th, 2016. This work is supported by National Natural Science Foundation of China (No. 91117009). 

Phenotypes of ptre1 mutant (left) and proposed model how PTRE1 regulates Aux/IAA protein degradation and auxin signaling (right). (Image by Dr. XUE Hongwei's lab)