Activation of the Fatty Acid α-Dioxygenase Pathway during Bacterial Infection of Tobacco Leaves

Abstract

A pathogen-induced oxygenase showing homology to prostaglandin endoperoxide synthases-1 and -2 was recently characterized by in vitro experiments as a fatty acid ␣-dioxygenase catalyzing formation of unstable 2(R)-hydroperoxy fatty acids. To study the activity of this enzyme under in vivo conditions and to elucidate the fate of enzymatically produced 2-hydroperoxides, leaves of tobacco were analyzed for the presence of ␣-dioxygenase-generated compounds as well as for lipoxygenase (LOX) products and free fatty acids. Low basal levels of 2-hydroxylinolenic acid (0.4 nmol/g leaves fresh weight) and 8,11,14-heptadecatrienoic acid (0.1 nmol/g) could be demonstrated. These levels increased strongly upon infection with the bacterium Pseudomonas syringae pv syringae (548 and 47 nmol/g, respectively). Transgenic tobacco plants overexpressing ␣-dioxygenase were developed, and incompatible infection of such plants led to a dramatic elevation of 2-hydroxylinolenic acid (1778 nmol/g) and 8,11,14-heptadecatrienoic acid (86 nmol/g), whereas the levels of LOX products were strongly decreased. Further analysis of oxylipins in infected leaves revealed the presence of a number of 2-hydroxy fatty acids differing with respect to chain length and degree of unsaturation as well as two new doubly oxygenated oxylipins identified as 2(R),9(S)-dihydroxy-10(E),12(Z),15(Z)-octadecatrienoic acid and 2(R),9(S)-dihydroxy-10(E),12(Z)-octadecadienoic acid. ␣-Dioxygenase-generated 2-hydroxylinolenic acid, and to a lesser extent lipoxygenase-generated 9-hydroxyoctadecatrienoic acid, exerted a tissue-protective effect in bacterially infected tobacco leaves.

Oxylipin Profiling of the Hypersensitive Response inArabidopsis thaliana

“…However, the induction of 13-LOX products dominated substantially over the 9-LOX products. The major difference between our results and previous studies on solanaceous plants is that in these latter plants mainly 9-LOX-derived oxylipins accumulated during development of HR (12)(13)(14)(15)(16)(17)23). In addition, we observed neither the activation of the ␣-DOX pathway nor formation of trihydroxy fatty acids.…”

“…The free acids and methyl esters of hydroxides, hydroperoxides, and ketols were quantified by normal phase HPLC, and fractions were collected of the 9-and 13-hydroxides and hydroperoxides for chiral phase HPLC (22). 2-Hydroxides and trihydroxides were determined by GC-MS as described previously (23). The free jasmonates were quantified by GC coupled to negative ion mass spectrometry after derivatization with pentafluorobenzyl bromide (22).…”

Leaf Oil Body Functions as a Subcellular Factory for the Production of a Phytoalexin in Arabidopsis

“…that resulted from infection with pathogenic bacteria (Hamberg et al, 2003;Vicente et al, 2012). A recent report suggested that 2-HOT correlated with defense activation during insect feeding in Nicotiana attenuata (Gaquerel et al, 2012).…”

9-Lipoxygenase-derived oxylipins activate brassinosteroid signaling to promote cell wall-based defense and limit pathogen infection

“…The biosynthesis of plant oxylipins is initiated by the action of 9-and 13-lipoxygenases, a-dioxygenases (a-DOX), or monooxygenases, all of which predominantly catalyze the oxygenation of linolenic acid (18:3) and linoleic acid (18:2) into reactive hydroperoxides, followed by secondary modification catalyzed mainly by cytochrome P450 enzymes or peroxygenases (Blée, 2002;Hamberg et al, 2002Hamberg et al, , 2003Andreou et al, 2009;Zoeller et al, 2012). Oxylipins can also be produced nonenzymatically from polyunsaturated fatty acids in the presence of singlet oxygen or by free radical-mediated oxygenation (Durand et al, 2009).…”