Arabidopsis B-cell lymphoma2 (Bcl-2)-associated athanogene 7 (BAG7)-mediated heat tolerance requires translocation, sumoylation and binding to WRKY29

To cope with stress and increased accumulation of misfolded proteins, plants and animals use a survival pathway known as the unfolded protein response (UPR) that signals between the endoplasmic reticulum (ER) and the nucleus to maintain cell homeostasis via proper folding of proteins. B-cell lymphoma2 (Bcl-2)-associated athanogene (BAG) proteins are an evolutionarily conserved family of co-chaperones that are linked to disease states in mammals and responses to environmental stimuli (biotic and abiotic) in plants. Molecular and physiological techniques were used to functionally characterize a newly identified branch of the UPR initiated by the ER-localized co-chaperone from Arabidopsis thaliana, AtBAG7. AtBAG7 has functional roles in both the ER and the nucleus. Upon heat stress, AtBAG7 is sumoylated, proteolytically processed and translocated from the ER to the nucleus, where interaction with the WRKY29 transcription factor occurs. Sumoylation and translocation are required for the AtBAG7–WRKY29 interaction and subsequent stress tolerance. In the ER, AtBAG7 interacts with the ER-localized transcription factor, AtbZIP28, and established UPR regulator, the AtBiP2 chaperone. The results indicate that AtBAG7 plays a central regulatory role in the heat-induced UPR pathway.