Figure 1.

Overview of the oxylipin biosynthesis pathways in P. patens (modified from [[22]]). 18:3(n-3) may be oxidized by one of the seven identified LOXes yielding 13-HPOTE(n-3). This compound is specifically dehydrated by PpAOS1 to 12,13-epoxy octadecatrienoic acid. The allene oxide is unstable and hydrolyses in aqueous solution non-enzymatically to α- and γ-ketols or cyclizes to a racemic mixture of 12-oxo phytodienoic acid (OPDA). In the presence of PpAOC1/2, however, enantiopure cis(+)-OPDA is formed. Analogous reactions are starting from 20:4(n-6) that is converted by PpLOX1/2 to 12-HPETE and further dehydarated by PpAOS1/2 yielding the unstable allene oxide derivative 11,12-epoxy eicosatetraenoic acid (11,12-EETE), which can be also non-enzymatically converted to the respective α- and γ-ketol derivatives or racemic cyclopentenones. Only in the presence of PpAOC2 formation of enantiopure 11-oxo prostatrienoic acid (11-OPTA) is possible.