title: Serotonin attenuates biotic stress and leads to lesion browning caused by a hypersensitive response to Magnaporthe oryzae penetration in rice.
abstract: The hypersensitive response (HR) of plants is one of the earliest responses to prevent pathogen invasion. A brown dot lesion on a leaf is visual evidence of the HR against the blast fungus Magnaporthe oryzae in rice, but tracking the browning process has been difficult. In this study, we induced the HR in rice cultivars harboring the blast resistance gene Pit by inoculation of an incompatible M. oryzae strain, which generated a unique resistance lesion with a brown ring (halo) around the brown fungal penetration site. Inoculation analysis using a plant harboring Pit but lacking an enzyme that catalyzes tryptamine to serotonin showed that high accumulation of the oxidized form of serotonin was the cause of the browning at the halo and penetration site. Our analysis of the halo browning process in the rice leaf revealed that abscisic acid enhanced biosynthesis of serotonin under light conditions, and serotonin changed to the oxidized form via hydrogen peroxide produced by light. The dramatic increase in serotonin, which has a high antioxidant activity, suppressed leaf damage outside the halo, blocked expansion of the browning area and attenuated inhibition of plant growth. These results suggest that serotonin helps to reduce biotic stress in the plant by acting as a scavenger of oxygen radicals to protect uninfected tissues from oxidative damage caused by the HR. The deposition of its oxide at the HR lesion is observed as lesion browning.
authors.affiliation: NARO Agricultural Research Center, 3-1-1 Kannondai, Tsukuba, Ibaraki, 305-8666, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Hayashi
authors.affiliation: College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa, Kanagawa, 252-0880, Japan.
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Fujita
authors.affiliation: NARO Agricultural Research Center, 3-1-1 Kannondai, Tsukuba, Ibaraki, 305-8666, Japan.
authors.forename: Taketo
authors.initials: T
authors.lastname: Ashizawa
authors.affiliation: NARO Agricultural Research Center, 3-1-1 Kannondai, Tsukuba, Ibaraki, 305-8666, Japan.
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Suzuki
authors.affiliation: National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Nagamura
authors.affiliation: NARO Agricultural Research Center, 3-1-1 Kannondai, Tsukuba, Ibaraki, 305-8666, Japan.
authors.forename: Yuriko
authors.initials: Y
authors.lastname: Hayano-Saito
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D006861:Hydrogen Peroxide / Q000378:metabolism; D020082:Magnaporthe / Q000502:physiology*; D012275:Oryza / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D010935:Plant Diseases / Q000382:microbiology*; D010937:Plant Growth Regulators / Q000378:metabolism*; D018515:Plant Leaves / Q000235:genetics / Q000276:immunology / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*; D013312:Stress, Physiological
chemical_list: D010937:Plant Growth Regulators; D017382:Reactive Oxygen Species; D012701:Serotonin; D000040:Abscisic Acid; D006861:Hydrogen Peroxide
keywords: Magnaporthe oryzae; Oryza sativa; abscisic acid; biotic stress; reactive oxygen species; rice blast; secondary metabolism; serotonin