Molecular chaperone that plays an important role in thermotolerance. Together with HSA32, required for long-term acquired thermotolerance (LAT) in plants and naturally high basal thermotolerance observed in germinating seedlings. Starts to accumulate in maturing seeds 15 days after pollination and decreases rapidly during seed germination. By heat stress and oilseed rape mosaic virus (PubMed:10760238, PubMed:10760305, PubMed:11489180, PubMed:16644052, PubMed:16995899, PubMed:17144892, PubMed:7866032). Regulated by HSA32 that retards its decay in a positive feedback loop (at protein level) during recovery after heat treatment (PubMed:23439916). No visible phenotype under normal growth conditions, but germinating seeds have greatly reduced basal thermotolerance and are unable to acquire thermotolerance (PubMed:10760305, PubMed:11489180). Faster degradation of HSA32 (at protein level) (PubMed:23439916). Over-expression of HSP101 partially reverse the sensitivity of 14 day-old seedling to heat stress. Belongs to the ClpA/ClpB family.