title: The isochorismate pathway is negatively regulated by salicylic acid signaling in O3-exposed Arabidopsis.
abstract: Ozone (O3), a major photochemical oxidant, causes leaf injury in plants. Plants synthesize salicylic acid (SA), which is reported to greatly affect O3 sensitivity. However, the mechanism of SA biosynthesis under O3 exposure remains unclear. Plants synthesize SA either by a pathway involving phenylalanine as a substrate or another involving isochorismate. To clarify how SA is produced in O3-exposed Arabidopsis, we examined the activities of phenylalanine ammonia lyase (PAL) and isochorismate synthase (ICS), which are components of the phenylalanine and isochorismate pathways, respectively. Exposure of Arabidopsis to O3 enhanced the accumulation of SA and the increase of ICS activity but did not affect PAL activity. In sid2 mutants, which have a defect in ICS1, the level of SA and the activity of ICS did not increase in response to O3 exposure. These results suggest that SA is mainly synthesized from isochorismate in Arabidopsis. Furthermore, the level of ICS1 expression and the activity of ICS during O3 exposure elevated in plants deficient for SA signaling (npr1 and eds5 mutants and NahG transgenics). Treatment of plants with SA also suppressed the enhancement of ICS1 expression by O3. These results suggest that SA synthesis is negatively regulated by SA signaling.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ogawa
authors.forename: Nobuyoshi
authors.initials: N
authors.lastname: Nakajima
authors.forename: Masanori
authors.initials: M
authors.lastname: Tamaoki
authors.forename: Mitsuko
authors.initials: M
authors.lastname: Aono
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kubo
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kamada
authors.forename: Hikaru
authors.initials: H
authors.lastname: Saji
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism*; D001483:Base Sequence; D015152:Blotting, Northern; D002827:Chorismic Acid / Q000378:metabolism*; D053138:Cyclohexenes / Q000378:metabolism*; D017931:DNA Primers; D019751:Intramolecular Transferases / Q000378:metabolism; D010126:Ozone / Q000494:pharmacology*; D010650:Phenylalanine Ammonia-Lyase / Q000378:metabolism; D020156:Salicylic Acid / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D053138:Cyclohexenes; D017931:DNA Primers; C052985:isochorismic acid; D010126:Ozone; D010650:Phenylalanine Ammonia-Lyase; D019751:Intramolecular Transferases; C058486:isochorismate synthase; D002827:Chorismic Acid; D020156:Salicylic Acid