Figure 3.

PMEIs modulate PME activity and DM of pectin in response to fungal and bacterial attack. Bacteria and fungi secrete pectin degrading enzymes, like polygalacturonases and pectate/pectin lyases, upon infection. PME activity leads to release of methanol, which serves as an alarm signal, activating the expression of pathogen-related PMEIs. Similarly, OGs, which are generated by degradation of pectin by fungal/bacterial PGs and PLs, serve as DAMPs, leading also to activation of defense related signaling pathways, which have been shown to activate PMEI gene expression. PMEIs inhibit PME activity leading to a higher degree of methylesterification of pectin, which contributes to resistance to fungal/bacterial enzymes resulting in less disease symptoms.