Functions in R gene-mediated resistance, but participates in a lower extent than SGT1B to RPP5-mediated resistance. Not required for RPM1, RPS2, RPS4 and RPS5-mediated resistance. Probably required for SCF-mediated ubiquitination, by coupling HSP90 to SCF complex for ubiquitination of HSP90 client proteins. Interacts with RAR1. Forms a ternary complex with RAR1 and barley HSP90. By infection with the oomycete H.parasitica (downy mildew) and heat shock. Belongs to the SGT1 family.