Control of plant Hsf function and stability by Hsp70/Hsp90 chaperones and the cochaperones Chip and Hop

Chaperones are essential cellular components involved in the control of protein homeostasis in all living cells. They are not only involved in the folding of newly synthesized proteins or refolding of denatured proteins, but also in a multitude of processes like protein import into organelles or signal transduction pathways. With respect to their role in these processes particularly the molecular chaperones Hsp70 and Hsp90 show a large functional versatility and are partially regulated by their cochaperones such as Chip (C-terminus of Hsp70 interacting protein) or Hop (Hsp70/90 organizing protein). While Hop connects the Hsp70 and Hsp90 chaperone machineries, Chip links the Hsp function to the 26S proteasome.

Recently we have shown that both chaperones play an important role in the control of function and stability of heat stress transcription factors HsfA1, A2 and B1 in heat stressed tomato cells (Solanum lycopersicon) (1). Based on these findings we have investigated the specific influence of Chip and Hop on this regulatory network in more detail. This was accomplished by using overexpression and knockdown approaches in the well established transient expression system in tomato mesophyll protoplasts.