Conjugation of dn-OPDA with amino acids inhibits its hormonal bioactivity in Marchantia polymorpha

Jasmonates are important phytohormones activating plant tolerance to biotic and abiotic stress, as well as different development processes. A conserved signalling pathway activated by distinct hormones in different plant species mediates these responses: dinor-12-oxo-phytodienoic acid (dn-OPDA) isomers in bryophytes and lycophytes, and JA-Ile in most vascular plants. The final responses depend, in many cases, on the accumulation of specialized metabolites. To identify novel compounds regulated by the dn-OPDA pathway in Marchantia, untargeted metabolomic analyses were carried out in response to dn-OPDA-regulated stress. A novel group of molecules were identified as dn-OPDA-amino acid conjugates (dn-OPDA-aas), and their accumulation after wounding and herbivory confirmed by targeted metabolic profiling in Marchantia and all species in which we previously found dn- iso -OPDA. Mutants in GRETCHEN-HAGEN 3A (Mp GH3A ) failed to accumulate dn-OPDA-aa conjugates, and showed a constitutive activation of the OPDA pathway and increased resistance to herbivory. Our results show that dn- iso -OPDA bioactivity is reduced by conjugation with amino acids. Therefore, a dichotomous role of jasmonate conjugation in land plants is highlighted: jasmonic acid (JA) conjugation with isoleucine (Ile) produce the bioactive JA-Ile in tracheophytes, whereas conjugation of dn- iso -OPDA with different amino acids disactivate the hormone in bryophytes and lycophytes.