Cytosolic HSP90 regulates the heat shock response that is responsible for heat acclimation in Arabidopsis thaliana

Plant survival requires the ability to acclimate to heat. plants are subjected to heat shock, the expression of genes is induced, and the plants become tolerant of higher We found that transient treatment with and radicicol, two heat shock protein 90 (HSP90) induced heat-inducible genes and heat acclimation in thaliana seedlings. Heat shock reduced the activity exogenously expressed glucocorticoid receptor (GR). Since activity depends on HSP90, this suggests that heat reduces cytosolic HSP90 activity in vivo. Microarray revealed that many of the genes that are up-regulated by heat shock and HSP90 inhibitors are involved in protein and degradation, suggesting that the activation of a maintenance system is a crucial part of this response. Most these genes have heat shock response element-like motifs their promoters, which suggests that heat shock factor (HSF) is involved in the response to HSP90 Several HSF genes are expressed constitutively in A. including AtHsfA1d. Recombinant AtHsfA1d protein the heat shock response element motif and interacts with thaliana cytosolic HSP90, HSP90.2. Overexpression of a negative form of HSP90.2 induced the heat-induciblegene. Thus, appears that in the absence of heat shock, cytosolic HSP90 regulates heat-inducible genes by actively suppressing function. Upon heat shock, cytosolic HSP90 is transiently which may lead to HSF activation.