May have a molecular chaperone role in the processing of secreted materials. Required for shoot apical meristem (SAM), root apical meristem (RAM) and floral meristem (FM) formation, probably by regulating the folding of CLAVATA proteins (CLVs). Also involved in pollen tube elongation (PubMed:11867518). Involved in resistance to tunicamycin- or high calcium-induced ER stresses. Possesses ATPase activity (PubMed:25297550). Interacts with FKBP42 (PubMed:12410806). Interacts with P23-1 (PubMed:20493581). A number of isoforms are produced. According to EST sequences. Ubiquitous. Seems inhibited by heat shock. Belongs to the heat shock protein 90 family.