Δ-dn--OPDA, a bioactive plant hormone of .

Significant progress has been recently made in our understanding of the evolution of jasmonates biosynthesis and signaling. The bioactive jasmonate activating COI1-JAZ co-receptor differs in bryophytes and vascular plants. Dinor-12-oxo-phytodienoic acid (dn--OPDA) is the bioactive hormone in bryophytes and lycophytes. However, further studies showed that the full activation of hormone signaling in requires additional unidentified hormones. Δ-dn-OPDAs were previously identified as novel bioactive jasmonates in . In this paper, we describe the major bioactive isomer of Δ-dn-OPDAs as Δ-dn--OPDA through chemical synthesis, receptor binding assay, and biological activity in . In addition, we disclosed that Δ-dn--OPDA is a biosynthetic precursor of Δ-dn--OPDA. We demonstrated that in planta -to- conversion of Δ-dn--OPDA occurs in the biosynthesis of Δ-dn--OPDA, defining a key biosynthetic step in the chemical evolution of hormone structure. We predict that these findings will facilitate further understanding of the molecular evolution of plant hormone signaling.