Plastid-produced interorgannellar stress signal MEcPP potentiates induction of the unfolded protein response in endoplasmic reticulum

Significance A defining characteristic of living organisms is dynamic alignment of cellular responses to stress through activation of signal transduction pathways essential for fine-tuning of interorgannellar communication. Uncovering these communication signals is one of the prime challenges of biology. We have identified a chloroplast-produced retrograde signal, methylerythritol cyclodiphosphate (MEcPP), as a trigger of unfolded protein response (UPR) required for restoration of protein-folding homeostasis in the endoplasmic reticulum (ER). Increased levels of MEcPP via genetic manipulation or exogenous application potentiate expression of a sub-set of UPR genes, and alter plant’s resistance to the ER stress inducing agent. These findings provide a link between a plastidial retrograde signal and transcriptional reprogramming of ER genes critical for readjustment of protein-folding capacity in stressed cells.