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). Probably involved in defense response. Chaperone involved in protein targeting to chloroplasts. May cooperate with SGT1 and HSP90 in R gene-mediated resistance towards the oomycete Hyaloperonospora parasitica (downy mildew). Plays a role with WPP-domain proteins in facilitating WIT1 nuclear envelope targeting (PubMed:12805626, PubMed:18065690, PubMed:19617588). Modulates stomatal aperture in response to various environmental conditions and physiological responses to the hormone abscisic acid (ABA) (PubMed:21586649). Binds to the deubiquitinating enzyme AMSH3. Interacts with SGT1B (via SGS domain). Interacts with OEP61. Interacts with HSFA1A/HSF1. Interacts with BAG3, BAG4 and BAG5. Interacts with WPP1, WPP2 and WIT1. Component of a ternary complex composed of WPP1, HSP70-1 and WIT1. Binds to TIR. A number of isoforms are produced. According to EST sequences. Expressed at a substantial level during normal growth in root, stem, leaf and flower tissues, but not in siliques (PubMed:8049382). Expressed in cotyledons, leaves, stems, vascular bundles, roots, stigmas and anthers (PubMed:28004282). Down-regulated during seed maturation. Up-regulated during germination. Induced by heat shock and cold (PubMed:11402207). Induced by dehydration stress and abscisic acid (ABA) (PubMed:8075396). Up-regulated by viral infection (PubMed:15805473). No visible phenotype under normal growth conditions (PubMed:21418353, PubMed:28004282, PubMed:26408532). The double mutants hsp70-1 and hsp70-4 exhibit accelerated bolting, flowering, and branching, small round shape and flat leaf blades, thin stems and short siliques (PubMed:28004282). The double mutants hsp70-1 and hsp70-4 exhibit reduced tolerance to abiotic stresses, such as heat, cold, salt and osmotic shock (PubMed:28004282). Plants overexpressing HSP70-1 show disabled immune responses, enhanced tolerance to heat shock and altered plant growth and development (PubMed:12805626). Plants overexpressing HSP70-1 are hypersensitive to abscisic acid (ABA) in seed germination assays, and are compromised in the dark- and ABA-induced stomatal closure (PubMed:21586649). Belongs to the heat shock protein 70 (TC 1.A.33) family. DnaK subfamily.