AtHsc70-1 negatively regulates the basal heat tolerance inArabidopsis thalianathrough affecting the activity of HsfAs and Hsp101

Heat shock protein 70 (Hsp70) chaperones are highly conserved and essential proteins with diverse cellular functions, including plant abiotic stress tolerance. Hsp70 proteins have been linked with basal heat tolerance in plants. Hsp101 likewise is an important chaperone protein that plays a critical role in heat tolerance in plants. We observed that Arabidopsishsc70-1mutant seedlings show elevated basal heat tolerance compared with wild-type. Over-expression ofHsc70-1resulted in increased heat sensitivity.Hsp101transcript and protein levels were increased during non-heat stress (HS) and post-HS conditions inhsc70-1mutant seedlings. In contrast,Hsp101was repressed in Hsc70-1 over-expressing plants after post-HS conditions. Hsc70-1 showed physical interaction with HsfA1d and HsfA1e protein in the cytosol under non-HS conditions. In transient reporter gene analysis, HsfA1d, HsfA1e and HsfA2 showed transcriptional response on theHsp101promoter.HsfA1dandHsfA2transcripts were at higher levels inhsc70-1mutant compared with wild-type. We provide genetic evidence that Hsc70-1 is a negative regulator affecting HsfA1d/A1e/A2 activators, which in turn regulateHsp101expression and basal thermotolerance.