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Oxylipins Produced by the 9-Lipoxygenase Pathway in Arabidopsis Regulate Lateral Root Development and Defense Responses through a Specific Signaling Cascade^[W]

^a Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, Campus Universidad Autónoma, Cantoblanco, E-28049 Madrid, Spain
^b Cell and Developmental Biology Department, John Innes Centre, Colney, NR4 7UH Norwich, United Kingdom
^c Division of Physiological Chemistry II, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-17177 Stockholm, Sweden

¹ To whom correspondence should be addressed. E-mail ccastresana{at}cnb.uam.es; fax 34-91-5854506.

Arabidopsis thaliana seedling growth with pure oxylipins resulted in root waving, loss of root apical dominance, and decreased root elongation. 9-Hydroxyoctadecatrienoic acid (9-HOT) was a potent inducer of root waving. Studies with noxy2 (for nonresponding to oxylipins2), a new 9-HOT–insensitive mutant, and coronatine insensitive1-1 (jasmonate-insensitive) revealed at least three signaling cascades mediating the oxylipin actions. Treatment with 9-HOT resulted in a reduction in lateral roots and an increase in stage V primordia. Roots showed strong 9-lipoxygenase (9-LOX) activity, and root primordia expressed 9-LOX genes. These results, along with findings that noxy2 and mutants with defective 9-LOX activity showed increased numbers of lateral roots, suggest that 9-HOT, or a closely related 9-LOX product, is an endogenous modulator of lateral root formation. Histochemical and molecular analyses revealed that 9-HOT activated events common to development and defense responses. A subset of 9-HOT–responding root genes was also induced in leaves after 9-HOT treatment or pathogen inoculation. The results that noxy2 displayed altered root development, enhanced susceptibility to Pseudomonas, and reduced the activation of 9-HOT–responding genes are consistent with mechanistic links among these processes. The nature of the changes detected suggests that oxylipins from the 9-LOX pathway function in cell wall modifications required for lateral root development and pathogen arrest.

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