nitiation of ER Body Formation and Indole Glucosinolate Metabolism by the Plastidia Retrograde Signaling Metabolite, MEcPP

Plants have evolved tightly regulated signaling networks to respond and adapt to environmental perturbations, but the nature of the signaling hub（s） involved have remained an enigma. We have previously established that methylerythritol cyclodiphosphate （MEcPP）, a precursor of plastidial isoprenoids and a stress- specific retrograde signaling metabolite, enables cellular readjustments for high-order adaptive functions. Here, we specifically show that MEcPP promotes two Brassicaceae-specific traits, namely endoplasmic reticulum （ER） body formation and induction of indole glucosinolate （IGs） metabolism selectively, via tran- scriptional regulation of key regulators NAIl for ER body formation and MYB51/122 for IGs biosynthesis）. The specificity of MEcPP is further confirmed by the lack of induction of wound-inducible ER body genes as well as IGs by other altered methylerythritol phosphate pathway enzymes. Genetic analyses revealed MEcPP-mediated COil-dependent induction of these traits. Moreover, MEcPP signaling integrates the biosynthesis and hydrolysis of IGs through induction of nitrile-specifier protein1 and reduction of the sup- pressor, ESM1, and production of simple nitriles as the bioactive end product. The findings position the plastidial metabolite, MEcPP, as the initiation hub, transducing signals to adjust the activity of hard- wired gene circuitry to expand phytochemical diversity and alter the associated subcellular structure required for functionality of the secondary metabolites, thereby tailoring plant stress responses.

Determinants of timing and amplitude in the plant general stress response

Plants have evolved intricate signaling cascades to rapidly and effectively respond to biotic and abiotic challenges. The precise timing of these responses enables optimal resource reallocation to maintain the balance between stress adaptation and growth. Thus, an in-depth understanding of the immediate and long-term mechanisms regulating resource allocation is critical in deciphering how plants withstand environmental challenges. To date however, understanding of this tradeoff has focused on the amplitude of long-term responses, rather than the timing of rapid stress responses. This review presents current knowledge on kinetics of secondary messengers involved in regulation of rapid and general stress responses, followed by rapid stress responsive transduction machinery, and finally the transcriptional response of a functional general stress responsive cis-element. Within this context we discuss the role of timing of initial peak activation and later oscillating peak responses, and explore hormonal and stress signaling crosstalk confounding greater understanding of these cascades.