Methyl-Jasmonate Functions as a Molecular Switch Promoting Cross-Talk between Pathways for the Biosynthesis of Isoprenoid Backbones Used to Modify Proteins in Plants

The modification of GFP-CaaL sensor proteins by geranylgeranyl groups in plants requires an active plastidial mevalonate (MVA)-independent pathway. As a consequence, fosmidomycin, a specific inhibitor of 1-deoxy-D-xylulose (DX)-5 phosphate reductoisomerase/DXR, the second enzyme in this so-called methylerythritol phosphate (MEP) pathway, impedes protein prenylation, which results in GFP-labeling of nuclei instead of the plasma membrane. In tobacco cells, a visual screen of conditions that allowed membrane localization of GFP-CaaL proteins in the presence of fosmidomycin, pinpointed jasmonic acid methyl esther (Me-JA) as a chemical able to overcome the inhibition in a gradual manner. Using Arabidopsis protein prenyltransferase loss-of-function mutant lines expressing GFP-CaaL proteins, we demonstrated that Me-JA induces a modification in protein substrate recognition by protein farnesyltransferase (PFT). Similar to Me-JA, farnesol and MVA also alter the protein substrate specificity of PFT, whereas DX and geranylgeraniol have limited or no effect. Our data indicate that stimulation of the MVA pathway adjusts the protein substrate specificity of PFT, which is corroborated with metabolic cross-talk of the origin of the prenyl group used to modify the protein. To illustrate how activation of the MVA pathway impacting PFT substrate specificity benefits a plant under stress conditions, a model is proposed.