Activation of the fatty acid alpha-dioxygenase pathway during bacterial infection of tobacco leaves. Formation of oxylipins protecting against cell death.
A pathogen-induced oxygenase showing homology to prostaglandin endoperoxide synthases-1 and -2 was recently characterized by in vitro experiments as a fatty acid alpha-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 alpha-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 alpha-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. alpha-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.
Hamberg
Mats
M
Division of Physiological Chemistry II, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden. Mats.Hamberg@mbb.ki.se
Sanz
Ana
A
Rodriguez
Maria Josefa
MJ
Calvo
Angel Pablo
AP
Castresana
Carmen
C
D001424:Bacterial Infections / Q000378:metabolism; D005227:Fatty Acids / Q000032:analysis / Q000096:biosynthesis*; D008084:Lipoxygenase / Q000378:metabolism; D009336:Necrosis; D010105:Oxygenases / Q000378:metabolism*; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000166:cytology / Q000201:enzymology / Q000382:microbiology; D030821:Plants, Genetically Modified; D044224:Pseudomonas syringae; D014026:Nicotiana / Q000201:enzymology* / Q000382:microbiology*
D005227:Fatty Acids; D010105:Oxygenases; D008084:Lipoxygenase