In cooperation with other chaperones, Hsp70s are key components that facilitate folding of de novo synthesized proteins, assist translocation of precursor proteins into organelles, and are responsible for degradation of damaged protein under stress conditions (Probable). Required for pollen development and pollen tube growth (PubMed:24486762). May be required for the early stages of female gametophyte development, but not for polar nuclei fusion during female gametophyte (PubMed:26251880). Possesses ATPase activity in vitro (PubMed:26186593). Binding to ERDJ3A activates the ATPase activity of BIP3. Interacts with BZIP28 (via C-terminus) (PubMed:23624714). Interacts with ERDJ3A (PubMed:26186593). Expressed in mature pollen grains, and pollen tubes. Induced by tunicamycin and DTT. Bip1, bip2 and bip3 triple mutation is pollen lethal (PubMed:24486762). Bip1, bip2 and bip3 triple mutation affects female gametophyte development during the early stages (PubMed:26186593). Belongs to the heat shock protein 70 (TC 1.A.33) family. DnaK subfamily.