Cytosolic heat shock protein 90 regulates heat shock transcription factor in Arabidopsis thaliana.

Plant survival requires the ability to acclimate to heat, which is involves the expression of heat-inducible genes. We found cytosolic heat shock protein (HSP) 90 serves as a negative regulator of heat shock transcription factor (HSF), which is responsible for the induction of heat-inducible genes in plant. Transient inhibition of HSP90 induces heat-inducible genes and heat acclimation in Arabidopsis thaliana seedlings. Most of upregulated genes by heat shock and HSP90 inhibitor treatments carry heat shock response element (HSE) in their promoter, which suggests that HSF participates in the response to HSP90 inhibition. A. thaliana HSP90.2 interacts with AtHsfA1d, which is one of the constitutively expressed HSFs in A. thaliana. Heat shock depleted cytosolic HSP90 activity, as shown by the activity of exogenously expressed glucocorticoid receptor (GR), which is a substrate of cytosolic HSP90. Thus, it appears that in the absence of heat shock, cytosolic HSP90 negatively regulates HsfA1. Upon heat shock, cytosolic HSP90 is transiently inactivated, and this may lead to the activation of HsfA1.