The co-chaperone HOP participates in TIR1 stabilization and in auxin response in plants.

HOP (HSP90-HSP70 organizing protein) is a conserved family of co-chaperones well known in mammals for its role in the folding of signaling proteins associated to development. In plants, HOP proteins have been involved in the response to multiple stresses, but their role in plant development remains elusive. Herein, we describe that the members of the HOP family participate in different aspects of plant development as well as in the response to warm temperatures through the regulation of auxin signaling. Our data demonstrate that Arabidopsis hop1 hop2 hop3 triple mutant shows different auxin-related phenotypes and a reduced auxin sensitivity. HOP interacts with TIR1 auxin co-receptor in vivo. Furthermore, TIR1 accumulation and auxin transcriptional response are reduced in the hop1 hop2 hop3 triple mutant, suggesting that HOP´s function in auxin signaling is related, at least, to TIR1 interaction and stabilization. Interestingly, HOP proteins form part of the same complexes as SGT1b (a different HSP90 co-chaperone) and these co-chaperones synergistically cooperate in auxin signaling. This study provides relevant data about the role of HOP in auxin regulation in plants and uncover that both co-chaperones, SGT1b and HOP, cooperate in the stabilization of common targets involved in plant development. This article is protected by copyright. All rights reserved.