Natural Elicitor 3,4-Dihydroxy-3-Methyl-2-Pentanone Induces Disease Resistance in Arabidopsis thaliana via Stereoisomer-Specific Activation of Defence Pathways

In contrast to bactericides, elicitors induce plant immune systems to defend against pathogen attack and avoid potential damage to the environment. However, the energy cost caused by the continuous activation of immunity leads to the inhibition of plant growth, which has limited the agricultural application of a large number of elicitors. Here, we identified a natural elicitor 3,4-dihydroxy-3-methyl-2-pentanone (DMPN) that can induce disease resistance in plants. DMPN contains four stereoisomers (3R,4S), (3S,4R), (3R,4R) and (3S,4S), which exhibit different induced resistance activities in <i>Arabidopsis thaliana</i> but do not inhibit plant growth. B1 is different from the other three isomers in that it only induces disease resistance to the necrotrophic pathogen <i>Erwinia carotovora</i> instead of the biotrophic pathogen <i>Pseudomonas syringae</i>, and the remaining isomers is effective for both pathogens. When it comes to threo-isomers B1 (3R,4S) and B2 (3S,4R), transcriptomic and gene expression analysis reveal that both B1 and B2 activated the jasmonic acid (JA)/ethylene (ET) and chitin-mediated signalling pathways. B2 also activated the salicylic acid (SA) pathway and upregulated a wider range of defence-related genes. These findings indicate that stereoconfiguration critically influences elicitor bioactivity. In summary, we reported a natural stereoisomeric elicitor, DMPN, which can elicit the plant defence response in <i>Arabidopsis thaliana</i> without inhibiting plant growth and revealed the differential inducing effects on the plant immune system of its four isomers.