Stress-mediated induction of MEcPP levels functions as a sensor and a communication signal to the nucleus that induces selected stress-responsive genes through alteration of nuclear architecture and functional dynamics.
Schematic model depicting alternative routes by which MEcPP potentiates induction of selected unfolded protein response (UPR) genes.
The MEcPP signal may function in the nucleus by first altering chromatin architecture and functional dynamics or by directly modulating a regulator of UPR. Alternatively, the MEcPP signal may, directly or indirectly, potentiate activation of selected UPR genes directly in endoplasmic reticulum (ER).
Simplified schematic models of MEcPP mode(s) of action in potentiating the general stress response (GSR).
Possible MEcPP signaling routes are depicted, including stress-mediated alteration in MEcPP levels functioning as a rheostat for the release of Ca2+ for the activation of CAMTA3; MEcPP-mediated alteration of chromatin architecture enabling the accessibility of RSRE for transcriptional regulators; MEcPP potentially functioning as an allosteric modulator of CAMTA3 or its potential coinducer; or a yet unknown transcriptional activator (factor X) binding to and activating RSRE, ultimately triggering the GSR.
The collective parallels between the essential role of the MEP pathway in eubacteria, apicomplexa, and plants expands the importance of our findings well beyond the plantae kingdom. Specifically, our discovery of MEcPP as a novel plastid-to-nucleus, stress-specific retrograde signal offers a unique opportunity to examine how a single primary signal is transduced into adaptive responses critical to the homeostasis of a biological system under unfavorable conditions. Indeed, defining the MEcPP signaling cascade, and how this system transduces the complex array of informational stress signals impinging on plants, may broaden our understanding of adaptive responses in eubacteria and perhaps to malaria.