Host-derived signals activate plant innate immunity.

Oligogalacturonides (OGs) are endogenous elicitors of defense responses released after partial degradation of pectin in the plant cell wall. Despite OGs cannot be considered true pathogen-associated molecular patterns, such as Flg22, they can be considered host-associated molecular patterns that are generated by the host cell during the infection process, and that stimulate the plant innate immune system. We have previously shown that, in Arabidopsis, OGs increase resistance to Botrytis cinerea independently of jasmonate, salicylic acid and ethylene. Recently, we demonstrated that, in Arabidopsis, OGs elicit a robust extracellular oxidative burst that is generated through the NADPH-oxidase AtrbohD. Moreover, we showed that this burst is dispensable either for early expression of OG-induced marker genes or for OG-induced resistance to B. cinerea. Similarly to Flg22, stimulation with OGs leads to the phosphorylation of mitogen activated protein kinase 3 and 6, suggesting that, even though different elicitors are perceived by distinct receptors, the signalling pathways mediated by these molecules converge very early and lead to the stimulation of the innate immune system.