Primary defined as the cellular receptors for immunosuppressive drugs, the immunophilins encompass two ubiquitous protein families. They consist of the FK506 binding proteins termed as FKBPs and cyclosporin binding proteins referred to as cyclophilins. They have been found in all orga- nisms. The 52 genes encode immunophilins have been identified in A. thaliana genome, among which 23 encode putative FKBP and 29 putative cyclophilins. Despite the various structure both families have peptidyl-prolyl cis/trans isomerase (PPIase) activity.