Involvement of the Arabidopsis alpha-DOX1 fatty acid dioxygenase in protection against oxidative stress and cell death.

alpha-dioxygenases (alpha-DOXs) catalyze the primary oxygenation of fatty acids into a newly identified group of oxylipins. Here we show that expression of the Arabidopsis alpha-DOX1 gene is induced in response to both incompatible and compatible bacterial infections. However, the level of alpha-DOX1 mRNA and dioxygenase activity appears earlier and reaches higher values when infection promotes a hypersensitive reaction. Furthermore, whereas gene expression is confined to necrotic lesions during the hypersensitive response, it occurs throughout the chlorotic area during a compatible interaction. Accumulation of alpha-DOX1 transcripts is impaired in SA-compromised plants and induced by SA and by chemicals generating nitric oxide (NO), intracellular superoxide or singlet oxygen, three signals mediating host cell death. Transgenic plants with altered levels of alpha-dioxygenase react like wild-type plants to a compatible pathogen. In contrast, plants with reduced activity develop a more rapid and severe necrotic response than wild-type plants to incompatible bacteria and paraquat treatment, respectively, and a milder response when alpha-DOX1 is overproduced. Our results suggest that plant alpha-dioxygenases are used to generate lipid-derived molecules for a process that protects plant tissues from oxidative stress and cell death.