A functional unfolded protein response is required for normal vegetative development in Arabidopsis

The Unfolded Protein Response (UPR) is activated in plants in response to ER stress and plays an important role in mitigating stress damage. We have analyzed an ire1a ire1b bzip17 triple mutant in Arabidopsis with defects in stress signaling and found that the mutant is also impaired in vegetative plant growth under conditions without externally applied stress. This raises the question as to whether the UPR functions in plant development in same manner as it does in responding to stress. bZIP17 is an ER-associated membrane transcription factor that is mobilized to the nucleus in response to stress. Through the analysis of a mobilization defective bZIP17 mutant, we found that bZIP17 must be capable of mobilization to support normal plant development. Likewise, through the analysis of ire1 mutants, we found that protein kinase and ribonuclease activities of IRE1 must be functional to support normal development. These findings demonstrate that the UPR is active, albeit at low levels, during unstressed conditions, and that these activities are required for normal development. Overall design: We examined gene expression by RNA-seq in Arabidopsis wide-type and mutant 17ab