Review: The unfolded protein response in development, defense, and stress

The unfolded protein response (UPR) is a eukaryote-wide signalling pathway in which unfolded proteins in the ER (often caused by abiotic stress) initiate signals transduced to the nucleus that lead to the expression of stress-response genes. Bao and Howell review the UPR in plants. They describe two ways that signals can move from the ER to the nucleus; in one, alternative RNA splicing of a bZIP transcription factor leads to the protein accumulating in the nucleus, and in the other different bZIP transcription factors are released from the ER and relocated to the nucleus. The review also discusses evidence, mostly from analysis of mutants, of the role of the UPR in hormone biology (auxin and brassinosteroids), vegetative and reproductive growth (including heat stress effects on pollen), and responses to pathogens. Front. Plant Sci. 10.3389/fpls.2017.00344