FIGURE 4.

Regulation of development and defense by plant oxylipins. Flowering plants like A. thaliana have 9-lipoxygenases and 13-ipoxygenases that catalyze the oxygenation of polyunsaturated fatty acids, mainly linoleic acid (18:2) and linolenic acid (18:3), to form fatty acid hydroperoxides. The resulting hydroperoxides are further metabolized to produce a variety of oxylipins, including hydroxy fatty acids and aldehydes, which play different roles in development and defense. α-Dioxygenase utilizes 18:2 and 18:3 to form 2-hydroperoxy fatty acids that are converted to 2-hydroxy fatty acids and aldehydes, with regulatory functions in plant defense against microbial pathogens and insects. The moss P. patens has besides polyunsaturated C18 fatty acids, polyunsaturated C20 fatty acids and can produce a broad range of oxylipins derived from them. P. patens 13-lipoxygenases and α-dioxygenase utilize mainly 18:2 and 18:3 as substrates producing similar oxylipins as in flowering plants, including (+)-cis-12-oxophytodienoic acid (OPDA), 2-hydroxy fatty acids and aldehydes with functions in development and defense against microbial pathogens. However, jasmonates are not synthesized in P. patens and the 9-lipoxygenase pathway seems not to be present. In addition, 12-lipoxygenases produce oxylipins from arachidonic (20:4) and eicosapentaenoic acids (20:5), including 12-oxo-dodecatrienoic acid (12-ODTE) and aldehydes whose functions are at present unknown.