Eicosapolyenoic fatty acids alter oxylipin gene expression and fatty acid hydroperoxide profiles in tomato and pepper roots

Eicosapolyenoic fatty acids (EP), such as arachidonic acid (AA), are abundant in oomycetes and can serve as microbe-associated molecular patterns (MAMPs) to elicit host defense responses. Solanaceous plants have multiple enzymes that convert EP into biologically active oxylipins. We evaluated expression of genes involved in oxylipin production in tomato and pepper seedlings with roots treated with AA and in tomato seedlings inoculated with Phytophthora capsici. AA treatment of tomato and pepper roots significantly increased expression of 9-lipoxygenase (9-LOX), 9-divinyl ether synthase (9-DES), alpha-dioxygenase (alpha-DOX), 13-lipoxygenase (13-LOX), and 13-allene oxide synthase (13-AOS), with 9-DES and alpha-DOX having the largest increases in expression. A similar pattern of expression was observed for 9-LOX, 9-DES, and alpha-DOX in tomato roots inoculated with P. capsici. Expression of 13-LOX and 13-AOS in tomato roots inoculated with P. capsici did not consistently follow the pattern observed in AA-treated tomato and pepper roots. AA treatment of tomato roots increased production of 9-LOX products of LA and AA, with no change in 13-LOX products of LA. These results implicate the 9-oxylipin and alpha-dioxygenase pathways in EP signal-response coupling, and establish that the EP response in tomato and pepper roots, generally the primary site of attack by soil-borne oomycetes, parallels that in other vegetative organs of potato and tomato.