Key chaperone involved in folding of secretory proteins in the endoplasmic reticulum (ER) lumen (Probable). Involved in ER quality control for seed storage proteins during seed maturation (PubMed:19567376, PubMed:21223397). Functions as a sensor of the ER stress response, and provides suitable conditions for the production of secretory proteins by alleviating ER stress (PubMed:19567376, PubMed:21223397). Interacts with P58A, P58B and ERDJ3B. Localizes close to the endoplasmic reticulum (ER) membrane complex of developing endosperm cells. Localizes to the periphery of the prolamine protein bodies which originate directly from the ER. During seed development, expressed from 5 to 20 days after flowering (DAF), with a peak at 10 DAF. Not expressed in mature seeds. By dithiothreitol-induced endoplasmic reticulum (ER) stress response (PubMed:21223397, PubMed:24153418). Induced by tunicamycin-induced ER stress response (PubMed:24153418). The kernels of the over-expressing transformant exhibit floury and shrunken features due to defects in seed storage proteins and starch synthesis. Belongs to the heat shock protein 70 family.