Molecular chaperone; assists the folding of proteins upon ATP hydrolysis. Known to play a role, in vitro, in the folding of actin and tubulin. Contributes to stem cell maintenance through its impact on transcription factors trafficking through plasmodesmata (PubMed:21868675). Probably involved in refolding translocated, partially unfolded proteins, including viral movement proteins (PubMed:21868675, PubMed:22476462). Heterooligomeric complex of about 850 to 900 kDa that forms two stacked rings, 12 to 16 nm in diameter (PubMed:11599560). Interacts with CCT3, KNAT1, STM and TTG1 (PubMed:21868675). Expressed in shoot meristems, root tip, vasculature and leaf epidermis. Lethal. Belongs to the TCP-1 chaperonin family.